For UK businesses developing hardware, one of the big decisions at the product development stage is determining how you would like the assembly of your PCB done. Would you like to send everything to the assembly partner, or would you like to source the components and send them along with the PCBs? This is what is known as the Turnkey PCB Assembly vs Consignment model. If you choose the model that is not appropriate to your business, the cost of assembly and lead times can dramatically increase and be significant for a startup.

The model that is most appropriate to the situation of almost all UK startups is the turnkey model of PCB assembly. When turnkey is used, the startup does not have to worry about sourcing the components, the suppliers of the components, as well as the supply chain of the components. This model is the most appropriate for a startup because it allows the startup to concentrate on the design and marketing of the PCB. The consignment model would only be appropriate for a startup that has a stock of components and suppliers of components, or that has strong control of the components.

Let’s examine that further, as well as where the exceptions are.

What Is Turnkey PCB Assembly?

PCB Turnkey assembly is where the partner that you have for manufacturing does everything in-house. This includes fabricating the bare boards, obtaining every component on your bill of materials (BOM), and doing the assembly and testing of the finished units. You supply the design files and get assembled and tested PCBs back.

This model is the most simple and most appropriate model for the majority of startups. The reason is that with the turnkey model, you have only one purchase order to deal with, one contact point, and one invoice.

What Is Consignment PCB Assembly?

With consignment (sometimes known as “free issue”), the client takes over responsibility. You source and supply all components and the PCB if you had them made elsewhere. The only responsibility for your assembly partner is the labour of placement, soldering, and inspection.

You get to maintain all the flexibility and control for what goes into your product, but you take on your share of the challenges and headaches, including sourcing, risks of counterfeit components, MOQs, MSL handling, storage, and distribution.

There is an interesting middle option: partial turnkey (or “kitted” assembly). This is where you supply some of the important components (like a programmed microcontroller) and your assembly partner takes care of everything else.

Turnkey PCB Assembly vs Consignment: A Comparison

Turnkey for Startups

1. Speed to Market:

The fast iteration capability of early-stage hardware gives a competitive edge. Turnkey offers a significant advantage with pre-established supplier relationships compared to going direct to stockists. Flexible sourcing is an invaluable service given the semiconductor supply constraints in recent years.

2. One Point of Accountability:

The biggest limitation of consignment is the finger-pointing opportunities when a batch fails. With turnkey assembly, your partner assumes the liability for the quality of each component. For a startup without a dedicated quality engineer, that’s a genuine safety net.

3. Concealed Expenses Eliminate:

On paper, consignment looks less expensive because you only pay for labour. However, most startups have trouble estimating:

• Minimum order quantities — you are forced to buy 2,500 resistors to get 200.
• Attrition stock — assemblers ask for a 5–10% buffer for small passive components for machines and loss.
• Shipping and import fees — buying from multiple suppliers means multiple shipments and customs delays if purchasing from the EU post-Brexit.
• Storage and handling — components that absorb moisture need baking and dry storage.
• Your own time — consignment is essentially a part-time job.

A turnkey quote simplifies and combines all of those costs, making forecasting cash flow—something all startup founders love—easier.

4. Design for Manufacture (DFM) Feedback:

Your turnkey partner is the first to look at your entire BOM and place an order. They are the first line of defense against obsolete components, footprints, and many other DFM issues.

Are you ready to begin production and scale from prototyping? Get a free turnkey assembly quote from Rush PCB UK and let us handle sourcing, assembly, and testing in our facility by uploading your Gerbers and BOM.

When Does Consignment Make Sense?

Turnkey is not the better option in all situations. Consignment (also partial turnkey) is a good option if:

• You have stock on hand. This could be if you overestimated component purchases during a dry spell or if you have leftover stock from a production run.
• You enjoy privileged supplier pricing. Some startups emerge from larger companies and bring with them supplier contracts that are superior to offers from an assembler.
• Your product has proprietary design or custom parts. Some of the specialized items you may need to keep are pre-programmed ICs, custom transformers, security components, or components that are under NDA.
• Traceability is a contractual obligation. In some medical, defense, or aerospace supply chains, you may be required to manage the source of the components personally.

Sometimes, however, partial turnkey offers the best of both worlds. Supply the two or three components that are critical and let your assembler cover the remaining ninety-seven components.

Turnkey PCB Assembly vs Consignment Cost Comparison: A Typical Startup Run

Imagine you are buying 100 assembled boards with an 80-line BOM. If you opt for consignment, you may have to place a large number of orders to different distributors, cover the shipping costs for all of them, accept some loss from the minimum order quantity on passive components, and spend two or three days of your engineers’ time on procurement and kitting. If you go for a turnkey solution, you pay a small markup for sourcing, but the assembler covers all of the volume purchasing, shipping, and kitting.

In our experience, for runs under a few thousand units, turnkey solutions are cheaper when factoring in the cost of the engineers’ time. True cost savings with consignment only happen at scale or with great supplier agreements.

Frequently Asked Questions

Does turnkey PCB assembly cost more than consignment?

The costs are essentially the same. Turnkey margins are typically lower than consignment costs for small to medium runs for startups because of minimum order quantity waste, self-sourcing costs, and the time spent on sourcing components.

Is it possible to combine both methods?

Yes, this is referred to as kitted assembly, where you can supply certain components, such as modified parts or programmed components, while the assembly house provides the balance. This method is practiced by most UK assembly houses.

What is the assembly time for turnkey PCB assembly in the UK?

Depending on components, the lead time for a prototype can be as short as five to ten working days. The lead time for consignment is totally dependent on how fast you can source and deliver your kit.

Does turnkey mean losing control of component quality?

Using a good assembly partner who can provide evidence of sourcing quality components from franchised distributors is an assurance of quality, and safety is often better than self-sourcing components with no supplier agreements. You should always ask your partner about their sourcing and quality assurance.

The Verdict

Turnkey PCB assembly makes sense for most UK startups. It brings together many benefits of PCB assembly, like reduced lead time, simplified procurement, and one accountable partner with, most of the time, a lower cost. Consignment is better when you have stock, have the components, or need to meet traceability standards. The same is true for mixed models (partial turnkey).

Read More: Lead-Free Soldering: Challenges, Best Practices & Why You Should Care

Rush PCB UK – Turnkey PCB Assembly vs Consignment: PCB Assembly Without the Stress!

Rush PCB UK has worked with many British startups to get them fully assembled and tested PCBs quicker than many of our competitors. Our turnkey solution encompasses fabrication, components sourced through franchised distributors, both SMT and TH assembly, and functional testing, all with UK support.

For a free quote, send your Gerbers and BOM to us, and we will reply within one working day with our pricing and lead times. We will also happily quote for consignment and partial turnkey.

A practical guide to lead-free assembly from the production floor at Rush PCB UK.

Lead-free soldering has been standard practice for all PCB assembly houses operating in Europe (and to a great extent worldwide) since the introduction of the EU RoHS directive back in July 2006. As regulation has tightened over the last decade or so, the electronics industry has had little choice but to adapt. Moving from the tried and tested tin-lead eutectic formula (63Sn/37Pb) to something less hazardous has been no small feat. Transitioning to SAC alloys (tin-silver-copper) remains a key challenge for production engineers everywhere.

The good news is that 15 years on from RoHS we have had plenty of time to optimise our assembly processes and fine-tune our specifications. With customer demands higher than ever and production/serviceable life expectancy (PSLE) requirements set to increase, how do we prepare for the future of lead-free assembly?

In this article, we cover:

• A brief history of lead-free regulation.
• Five key technical challenges to assembling PCBs without lead.
• Best practices for getting great yields with lead-free soldering.
• Key differences between lead-based and lead-free soldering.
• Why your next project will benefit from lead-free assembly.

RoHS Regulation Explained

So what exactly is the RoHS directive, and why does lead solder suddenly become such a problem?

The Restriction of Hazardous Substances (RoHS) Directive 2011/65/EU was first introduced by the EU parliament in July 2006. RoHS specifically targets electrical and electronic products being placed on the market by restricting seven hazardous materials, lead (Pb) being one of them.

Prior to the regulation, solder paste used for wave and reflow assembly consisted primarily of a tin and lead eutectic alloy. Tin-lead solders have been used since at least the mid-19th century and remain one of the easiest metals to work with due to its low melting temperature (183 °C) and good wetting ability. In order to comply with the new directive, manufacturers replaced lead with less harmful alternatives like silver and copper.

Nowadays, SAC305 (96.5% Sn, 3.0% Ag, 0.5% Cu) is by far the most popular lead-free alloy specified for solder paste. SAC alloys are called eutectic when they meet the following percentages: 99.3% Sn, 0.7% Ag, 0.05%Cu. This has a melting temperature of 221 °C making it ideal for lead-free applications.

During our transition to lead-free assembly at Rush PCB UK, we were able to leverage existing supplier relationships to source lead-free solder paste with a minimum silver content of 3%. It wasn’t as simple as swapping solder paste however; thermal profiles had to be re-engineered, component qualifications carried out, and investments made into reliable high-temperature equipment.

Lead-Free Soldering: Top 5 Technical Challenges

1. Higher Melting Point, Narrower Process Window

Lead-free solder paste has a higher melt temperature of roughly 34 °C compared to SnPb eutectic. This extra thermal load can exceed the glass transition temperature (Tg) of many standard substrates making process control more critical than ever. Many off-the-shelf FR-4 materials have a Tg rating of 130 °C – 170 °C which gives little headroom between maximum reflow temperatures and delamination of the board. For this reason, high-Tg substrates (Tg ≥ 170 °C) are recommended for lead-free assembly.

2. Tin Whisker Growth

Tiny hair-like crystals known as tin whiskers can grow spontaneously from pure tin surfaces. These conductive crystals can reach lengths of several millimetres and pose a significant reliability risk by shorting adjacent circuits. Growth is most prevalent in densely packed assemblies with large areas of exposed tin-plate. Mechanisms for whisker growth are still not fully understood but are thought to be linked with compressive stress in the tin layer. Formation of intermetallics (Cu6Sn5) at the copper-tin interface is one such cause. Conformal coating, nickel barrier layers, and choosing the right PCB surface finish can help reduce tin whisker growth.

3. Brittle Solder Joints / Intermetallic Growth

Lead-free solder forms intermetallic compounds (IMCs) with copper pads during reflow. The primary IMCs you will find at the solder-pad interface are Cu6Sn5 and Ag3Sn. Intermetallic formation is desirable up to a point — we need those metal compounds to create a metallurgical bond between components and PCB. Too much intermetallic growth at the solder interface results in brittle fracture when exposed to shock or vibration. Lead-free SAC solder joints are much more prone to cracking under stress than lead-based equivalents. Brittle fractures are typically the result of thermal or mechanical shock; components exposed to frequent temperature fluctuations or vibration are more likely to fail.

Automotive PCBs and aerospace applications are a prime example where lead-free SAC alloys are used but stringent reliability requirements limit their application.

4. Poor Wetting Ability

Lead-free solder simply does not wet like tin-lead. Surface tension is significantly higher which means solder will not spread across pads and component leads as easily as before. Insufficient solder fillets, solder bridges, and head-in-pillow defects are commonplace when hand-optimising lead-free assembly parameters. Specific flux formulations become even more important when working with SAC alloys. No-clean, halide-activated pastes work best for us at Rush PCB UK. A nitrogen environment is also beneficial for achieving high-quality leads.

5. Component / Substrate Compatibility

Something that is often overlooked during the transition to lead-free assembly is that not all components are created equal. Maximum body temperature ratings are specified for all components, many of which do not exceed 217 °C. Simply put, exposing components to temperatures outside of their specification, even for a couple of minutes, can cause irreparable damage and affect long-term reliability. Parametric shift, bond wire lift, and internal delamination are all possible outcomes of over-temping sensitive devices.

Best Practices When Working Lead-Free

– Reflow Oven Profiling

Good thermal profiling is by far the most important aspect of assembly yield. A standard SAC305 reflow profile looks something like this:

• Preheat (ramp 1–3 °C/s) to ~150 °C
• Thermal soak (between 150–200 °C) for ~60-120s
• Reflow (TaL — time above liquidus) >217 °C for ~45-90s
• Peak temperature between 235–250 °C
• Cooling (ramp down ~3–4 °C/s)

We tend to use thermocouple test boards to profile new assemblies ensuring ΔT across the PCB doesn’t exceed ±5 °C.

– Moisture Sensitivity Level (MSL) Management

Higher reflow temperatures required for SAC alloys significantly increase the risk of ‘popcorn’ cracking if components are not correctly stored or baked. All components with an moisture sensitivity level (MSL) of 3+ should be kept in dry cabinets or vacuum sealed moisture barrier bags. Component floor life starts from the day of packaging and will vary from manufacturer to manufacturer. Most commercial components have a floor life of 168 hours (1 week). If the floor life has been exceeded, a moisture bake at 125 °C for the times stated in the datasheet is required before assembly.

– PCB Surface Finish

Surface finish selection is crucial when working lead-free for many reasons:

• Solderability and shelf life.
• Long-term joint reliability.
• Component compatibility.

Here are our thoughts on the most common PCB finishes:

• ENIG: Excellent wetting properties and solderability. Provides flat surface ideal for fine-pitch components. Lead-free assemblies are also less prone to tin whisker growth thanks to the nickel barrier layer. However, gold-nickel plating can result in black-pad if not applied correctly.
• Lead-Free HASL: One of the cheapest and most robust finishes around. Uneven surface can cause issues with fine-pitch QFP/BGA components.
• OSP: Inexpensive and provides a flat surface but has very limited shelf life. Performance degrades rapidly after first reflow.
• Immersion Tin: Good flatness and solderability but prone to tin whisker growth without additional barriers.

We recommend discussing finish options with your fabricator during their design-for-manufacture (DFM) review stage.

– Wave Soldering

Wave soldering with lead-free solder also requires higher bath temperatures (~260 °C) than traditional SnPb processes. More dross, erosion of stainless steel/cast iron components in the solder pot, and special attention to flux formulations all add to the operational costs. Selective soldering systems allow for much more controlled soldering of through-hole components on boards with heat-sensitive SMDs on the top side.

Lead-Based vs Lead-Free Assembly Summary

Read More: Surface Mount Technology (SMT) vs Through-Hole (THT): Explained!

Why Rush Can Help with Your Next Lead-Free Project?

The challenges of lead-free assembly should not deter you from migrating away from legacy hardware. Doing so will only improve your product’s reliability and allow access to markets that require RoHS compliance. Yes, the process is more demanding. Inspection is more rigorous (X-ray for BGAs! ), and incoming material specifications are more robust. But who doesn’t like a challenge?

At Rush PCB UK we’ve invested in industry-leading convection reflow ovens with onboard nitrogen generation. Our AOI/X-ray inspection machines are calibrated and automated, and we even store moisture sensitive components in a climate-controlled facility. All of our production engineers are trained to IPC standards and we offer full traceability on all jobs.

Got questions? Get in touch with our team today or request an instant quote now!

When designing a PCB, reliability starts with stackup. When planning copper thickness and trace width engineers must consider current capacity and thermal rise of every signal. Too thin, and your board may overheat, have a high voltage drop or lift off the board entirely. With devices becoming smaller and voltages continuing to increase it’s more important than ever to understand PCB design rules.

What Is PCB Copper Thickness?

Put simply, PCB copper thickness is how tall the copper column is on any layer of a PCB. PCB copper thickness is typically defined in terms of “copper weight” ($oz/ft^2$).

How Much is 1 oz Copper?

The reason manufacturers define copper thickness in $oz/ft^2$ is that this is typically how fabricators buy copper foil. Think of it like grocery store meat labels. Instead of defining a steak as “¾” thick, butchers will sell by the pound.

Certain manufacturers will start with different base copper thicknesses, called the finished copper thickness. Since both Electroless copper and Electrolytic copper are added during PCB manufacturing your designer must be aware that the “1 oz PCB” may actually be 0.85 or 1.15 oz after finishing.

What Is Trace Width?

The PCB trace width is how wide the copper trace is. Unlike copper thickness, this is the primary dimension that a designer can control to increase current while limiting a specified temperature rise.

Current versus Temperature Rise:

Current flows through a trace like any other resistor. As current increases, the temperature of the trace will also increase. For a set voltage drop, we can use Ohm’s law ($P = I^2R$) to see why increasing current means more heat.

If we want to limit the value of R (resistance), we must increase the cross sectional area of the copper. Quite simply, wider copper = less resistivity. Since most PCB designers will set their stackup with a fixed height for copper thickness, the designer is usually free to increase the width of a trace to whatever is needed.

Internal vs External PCB Traces:

However, there are differences between internal and external layers when it comes to thermal dissipation:

• Internal Layers: Since internal layers are “sandwiched” by an insulating dielectric material (FR4), they do not cool as well as an external layer.
• External Layers: External traces benefit from convection and radiation into the surrounding air.

A design rule of thumb is that an internal trace must be about twice as wide as an external trace to handle the same amount of current. Combined, copper thickness and trace width define the total cross sectional area of a copper trace.

$$Area = Width_{[mil]} \times Thickness_{[mil]}$$

Design Tradeoff

Unfortunately, not every PCB has the luxury of wide traces. Maybe your routing is limited by large reference designators or you’re designing for fine-pitch components. Ball Grid Arrays require very small spacing between pads, which often limits your routing options.

What do you do if you can’t make your trace wide enough? You make it tall. Designing for heavy copper PCBs is one way to save horizontal space by using the vertical height.

When you increase copper thickness, you can route narrower traces while still maintaining the same current and thermal rise. The tradeoff is that heavy copper (2 oz, 3 oz) cannot be routed as closely together since the chemistries used to etch the copper will likely short those traces together.

To Calculate Width for PCB Trace Widths

The good news is that this isn’t a guessing game. Like most things in engineering, we have empirically derived formulas and industry standard tables to tell us what size each trace needs to be.

The Theory

First, we need to know three things:

1. Target Current (A): The maximum current you expect to flow through the trace at any time.
2. Allowed Temp. Rise (°C): How much hotter can you let the trace get compared to surroundings. (Typically 10°C or 20°C)
3. Copper Thickness oz (or mils)

If we have an assigned or pre-selected copper thickness we can calculate the required width.

Can We Use a Standard?

Yes! This is where IPC-2221 comes in handy. If you don’t know about IPC-2221 you’re likely using it right now. The graphs below are taken from IPC-2221 and plot Trace Width vs Current for a variety of temperature rises and copper thickness options.

IPC Copper Thickness and Trace Width Standards

• IPC-2221: Standard calculations.
• IPC-2152: Use for High Power / Accuracy.

The IPC-2221 standard has been updated several times since it was first drafted as MIL-STD-275. The latest version, IPC-2221B, offers more detailed guidelines and calculations for designers to follow.

And IPC-2152 is the latest, high-fidelity standard for current-carrying capacity in PCB design. It takes more variables into account, such as thermal conductivity of your substrate material.

Applications Requiring Higher Currents

Don’t let the term “Power PCB” fool you. Many electronics require large amounts of current to function, even if they are not powering a motor. Here are a few common examples:

• HMS and BMS: Battery system board require frequent high current connections to the battery cells.
• Power regulation: Large switching regulators can put out 10A or more on a single leg.
• Motor Controllers: DC and AC motor drivers typically require large input currents.
• UPS: Uninterruptable power systems need to supply large loads when the input power fails.

Heavy Copper PCBs

Heavier copper PCBs aren’t just for increasing current capacity. The additional copper also helps to pull heat away from high-power components (think: MOSFETs), dissipating heat across the entire board.

Signal Integrity PCB Design

The flip-side of heavy current traces are signal traces. Signal traces aren’t concerned with how much current they can carry, but rather how they affect signal. When designing for signal integrity, we care about controlling PCB trace resistance and ensuring that voltage drop doesn’t cause our components to fail.

What About High-Speed Signals?

Ok, high-speed signals do care about current, but indirectly. High speed signals are generally controlled by the PCB trace width and target impedance. Oftentimes high-speed signals are designed to 50 ohms single-ended or 100 ohms differential. To properly calculate these widths, your fab will need to control copper thickness to a much higher tolerance.

Increasing copper thickness will decrease the impedance of your trace (ouch), and varying copper thickness can cause serious signal integrity issues like EMI and signal reflection.

Mistakes To Avoid

• Forgetting Internal vs External: Placing wires that are only wide enough for a signal trace on a power rail.
• Not Doubling Width on Internal Layers: Not accounting for the fact that internal layers are slower to heat dissipate than external layers.
• SPECING 3 OZ WHEN 1 OZ WOULD WORK: Increasing copper thickness will increase cost and make very fine-pitch components impossible to etch.
• No Thinking About Manufacturing Tolerances: Remember most PCB manufacturers etch away copper to create your traces. This means that the finished width of your traces will be smaller than what you designed.
• Never Checking the PCB Power Plane Sizes: After sizing every trace on your board, be sure to check the power plane sizes match up as well.

Frequently Asked Questions

1. What thickness is considered 1 oz copper on PCB?

After plating, 1 oz copper is around 35 microns thick.

2. Is more copper better?

Not necessarily. More copper equals more current and reduced thermal rise, but comes at the cost of price and manufacturing constraints. Heavier copper PCBs are more difficult to etch fine-pitch components.

3. Does copper thickness matter for signals?

Just like power circuits, signal circuits also have to worry about voltage drop across their traces. For low voltage logic signals (1.2V, 1.8V) even a small drop can cause the circuit to not work correctly. Increasing copper thickness or trace width can help reduce this.

4. What standard is used for trace width?

IPC-2221 is still considered the industry standard for trace width calculation. However, for higher fidelity designs and high power applications, IPC-2152 is the better standard to use.

5. Could my manufacturer change copper thickness?

Typically this is something that is changed at the panel level. Most manufacturers won’t be able to provide you with 2 different copper thicknesses on the same internal layer. Be sure to specify your finished copper thickness in your fab notes or stackup PDF.

Any type of electronic project involving PCBs or printed circuit boards requires soldering, whether it uses through-hole components or surface-mount components. Soldering anchors the electronic components mechanically to the PCB, while also providing good electrical conductivity between the component terminals and the copper pad on the board. The role of flux in the soldering process is one of reduction. Over time, exposure of the copper pad and the component terminals leads to the formation of oxides. This layer of oxides hinders proper wetting of the soldering surfaces by molten solder, ultimately leading to a dry joint. Not only is a dry joint mechanically weak, but it also has poor electrical conductivity.

The Role of Flux in Soldering:

Keeping the solderable surface coated with flux helps reduce the oxides when applying molten solder. This allows the solder to interact with the solderable surfaces on the board and on the component terminals. Upon cooling, the solder bonds with these surfaces, producing a strong and clean mechanical joint and good electrical conductivity.

Why does Flux Matter?

As a chemical compound, you will typically apply the flux to the metal surfaces before soldering. The application of heat causes the flux to clean the metal surfaces by removing impurities and oxides. This also allows the molten solder to flow smoothly over the surface, while preventing new oxides from forming during the soldering process. Without flux, the solder joint could be weak, dry, and even fail.

Types of Flux Available

Depending on the melting metal, flux ensures the joint is not only strong, but clean and electrically reliable. However, there is a large variety of flux types available, and picking the right one can feel overwhelming.

In this article, we at Rush PCB UK explain the types of flux available, their properties, and when you should use a specific type of solder.

1. Rosin Flux:

Rosin flux is the most commonly used flux in electronics work. Made from pine sap, it is refined into a sticky liquid or amber-colored paste. Depending on their activity level, rosin flux is subdivided into three subtypes. Note that the more active the flux is, the more aggressively it will clean the metal surface.

 – Non-Activated (R)

This type of flux is barely active and mostly used on clean, shiny surfaces. Common examples of use are on pre-tinning wires that require minimal cleaning.

– Mildly Activated (RMA)

This type of flux offers more cleaning power and is best suited for soldering general electronic circuit boards.

– Fully Activated (RA)

This type of flux is super aggressive and used for highly oxidized or dirty metal surfaces. Common examples are old rusty surfaces. It is also sticky and highly corrosive, and requires thorough cleaning with alcohol after application.

2. Water-Soluble Flux: 

Water-soluble flux not only provides strong cleaning of the solderable surfaces, but is also easy to clean up after soldering. This is because it is typically made from chemicals like acids or amines that dissolve easily in water. Being more aggressive than rosin flux, water-soluble flux is commonly used for metals with a greasy or heavily oxidized surface.

As water-soluble flux is very corrosive, it is necessary to clean the surface after soldering to prevent damage. Fortunately, cleaning requires only a brush and warm water.

3. No-Clean Flux:

No-clean flux is a modern option meant to save time. This is a synthetic or a rosin-based flux. It produces a minimal residue that is also non-corrosive, and you may safely leave it on the project. Much less aggressive compared to water-soluble flux, the no-clean flux works well for clean or lightly oxidized surfaces.

No-clean flux is perfect for modern high-density and high-volume electronics, where it is impractical to stop to clean every joint.

However, as the no-clean flux is not aggressive enough, it is not very effective for heavily oxidized metal surfaces. Moreover, the residue can look untidy when visible in decorative projects.

4. Acid-Based Flux:

Made with strong acids, the acid-based flux, also known as inorganic flux, is the muscle of the industrial world. Used extensively in industrial soldering, it is designed for soldering tough metals such as heavily oxidized copper, brass, steel, stained-glass, and in plumbing.

Being highly corrosive, it is essential to clean acid-based flux with water or a neutralizer to prevent the flux residue from corroding your project. Moreover, due to its corrosive nature, it is not advisable to use acid-based flux on electronic projects, as it is likely to destroy circuits.

Type of Flux to Use

Fluxes are available in different types. Each type is suitable for specific materials, environments, or soldering methods. Depending on your application, you can use:

1. Flux-Core Solder Wire

This is a beginner-friendly method to apply flux while soldering. The solder comes in the form of a hollow wire, and the hollow space contains liquid flux. As you melt the solder, it automatically releases the flux, which flows out from the wire to clean and prepare the surface for a good joint.

However, the flux in the solder wire is not very corrosive, and therefore, the combination does not work for PCB pads or components that are heavily oxidized. For such cases, you must add extra flux separately.

2. Flux Paste

This flux has a thick consistency and is a paste of solder and flux. This combination is mostly suitable for SMD components and other precision soldering jobs. You can apply it with a toothpick, brush, or syringe to control the amount and the location.

In the electronic industry, it is common to use it with an automatic dispenser or apply it through a silk screen, before placing the component on it. The flux holds the tiny components in place until the assembly passes through the reflow oven, when the solder melts and anchors the components on the board.

3. Liquid Flux

Liquid flux is useful for general-purpose electronic soldering and precision repair work. Easy to apply using a cotton swab, syringe, pipette, or even a small brush, this type of flux is very versatile for manual work.

4. Flux Pens

This is another variation of the liquid flux, available in a convenient pen form. Using it is very simple, as you can apply the flux exactly where needed, and it will not create a mess or waste. This is very useful for small manual touch-ups and quick jobs on your circuit.

Related: In-Circuit Testing vs. Functional Testing: Key Differences and Applications

Conclusion

At Rush PCB UK, we recommend using flux when soldering—it is necessary. However, you must pick the right one for the purpose, and our article should help you to do that.

Your Comprehensive Guide to Essential PCB Components for Beginners

PCB Components are also known as parts in the circuit board industry. The components/parts have a very important role in the PCB industry. These parts are the fundamental building blocks of all electrical devices, from basic consumer electronics to sophisticated supercomputers. There are various types of components in the PCB Industry to complete a circuit complete with the required outputs.

The process of choosing parts for the circuit is based on the outputs the product has to give. It’s a product developer EE engineering responsibility to select the right component for the circuit which should be controlled with input voltages.

As per present innovations, the RF signals are an essential factor for designers to look into for which they have to ensure they are selecting the right components. The second most important factor is the dimensions & size of the product which also becomes a challenge for the designer to select the smallest component in dimension as per the values required.

Resistors

As we know the basic understanding of Resistors are to resist the obstructed flow of electrical current to a certain degree. The unit of the resistor is Ohms (Ω) and the symbol in the PCB industry is used is as ‘R’.

There are numerous varieties of resistors, each with unique properties and applications. Typical resistor types include the following:

Fixed resistors provide a fixed resistance value that is reliable and predictable. They can be divided further into wire wound resistors, metal oxide resistors, metal film resistors, and carbon composition resistors.

Variable resistors, you can automatically or manually change the resistance value. They can be found in many different forms, such as trim pots, rheostats, and potentiometers.

Special resistors have special qualities or capabilities. Varistors, photoresistors, and thermistors are a few examples. There are various packages used in the PCB industry for resistors such as:

Through-Hole Resistors: These resistors have leads that are inserted into holes drilled in the PCB and are soldered on the opposite side. They typically come in: Axial: The most common form with leads on both sides (e.g., 1/4W resistors). Radial: Leads are on the same side, and often used for compact designs.

Surface-Mount Device (SMD) Resistors: These are more compact and are soldered directly onto the surface of the PCB. Common sizes include:

0402 (1.0 mm × 0.5 mm): For very compact designs.

0603 (1.6 mm × 0.8 mm): A widely used size in consumer electronics.

b0 mm × 1.25 mm): Popular in slightly larger applications.1206 (3.2 mm × 1.6 mm): Often used for power resistors where more heat dissipation is required.

These resistors can be made from different materials like metal oxide, thick film, or wire wound, depending on the application. There are various manufacturers such as Vishay, Yageo, and TE Connectivity​ which do manufacture the resistors for the PCB Industry.

The Capacitor

Electronic parts called capacitors can store and release electrical energy. It is made up of two conductive plates divided by a dielectric, which is an insulating substance. Typical capacitor types include the following:

1. Ceramic capacitors

Because of their small parasitic resistance and inductance, ceramic capacitors which are constructed of ceramic materials are frequently employed in high-frequency applications. Their capacitance values range from picofarads (pF) to microfarads (µF), and they are usually modest in size. Most of the ceramic capacitor are surface mount devices.

 Common surface mount packages of  ceramic capacitors are as:

• 0805 is 2.0×1.3mm
• 1210 is 3.2×2.5 mm
• 0603 is 1.5×0.8mm
• 1206 is 3.0×1.5mm
• 0402 is 1.0×0.5mm
• 1812 is 4.6×3.0mm

Electrolytic capacitors: Comparing electrolytic capacitors to ceramic capacitors, the capacitance value of the former is usually higher, ranging from microfarads (µF) to millifarads (mF). In power supply circuits, they are frequently utilized for filtering and energy storage. Because they contain a positive and negative terminal and are polarized, electrolytic capacitors need to be linked in a circuit correctly.

 Through-hole capacitors: Some common through-hole packages of electrolytic capacitors are

Axial: The cap has leads exiting from both ends. Usually positioned perpendicular to the board. Some common axial packages of electrolytic capacitors are 1205,1207,1306,1411,1148.

Radial: One end is where both leads exit. Usually attached to the board vertically.  Electrolytic radial capacitors come in different packages like 3.3uF ,100uF 220uF with different voltage capacities.

2)  Surface Mounted Devices (SMDs):

These are intended to be built or soldered by automated equipment. SMD capacitors come in packages like 10uF ,100uF 47uF ,33uF. Their voltage range also varies depending upon the capacitance.

Film capacitors

Film capacitors are renowned for their stability, minimal distortion, and broad temperature range. They are constructed from thin plastic films. They are frequently utilized in radio and audio frequency circuits. Film capacitors range from 0.1uF to 1000pF they typically come in radial packages with different voltage values.

There are several uses for capacitors in electronic circuits. Typical applications include the following:

1. Energy storage coupling
2. Decoupling timing filters

Inductors

Another kind of passive component seen on circuit boards is the inductor. When an electric current flows through them, they are utilized as energy storage devices in magnetic fields. Inductors are frequently employed in electric circuits, such as filters, oscillators, and transformers, where the ability to control current over time is essential.

Typical inductor types include the following:

Air-core inductor: The only core in an air-core inductor is air. Due to their low inductance, these inductors are frequently utilized in high-frequency applications that call for low inductance values.

Ferrite core inductors: Ferrite is a magnetic ceramic substance that is used to make the core of ferrite-core inductors. Ferrite-core inductors are employed in many different applications, such as power supply and radio frequency circuits, and have larger inductance values than air-core inductors.

 Iron-core inductors: An iron or iron alloy core is used in iron-core inductors. These inductors are frequently utilized in power applications due to their high inductance values.

 There are several uses for inductors in electronic circuits. Typical applications include the following:

• Energy storage
• Filters
• Oscillatory circuits
• Transformers

Inductor packages

Through-hole

Axial: Although their color makes them easy to identify, resistors are frequently confused for axial inductors. This kind of inductor is made by wrapping a dumbbell-shaped ferrite core with extremely thin copper wire and connecting its top and bottom with lids. There are several sizes available for axial leaded inductors, including 2.8x5mm, 3.0x7mm, 4.0*10mm, 5.0x10mm, and 6.5x12mm.

Radial: Because they are wound on a cylindrical bobbin, similar to axial inductors, radial inductors are also known as bobbin-based inductors. These are mostly utilized for printed circuit board mounting. It is made up of two different kinds of leads: radial and axial leads.

Inductors with Surface Mount Packages:

Surface mount inductors, or SMD inductors, are a form of inductor that is placed on the surface of the PCB, instead of the standard through-hole technique. They have soldered pads that are attached to the PCB in order to form an electrical circuit. SMT inductors have typical inductance between 2.2uH and 680uH.

Transformers:

Transformers are used to move electrical energy, either with a higher or lower voltage, from one circuit to another. It is possible to refer to the voltage as “transformed.” Like inductors, they are made of a soft iron core encircled by at least two wire coils: a secondary coil for the circuit to which energy is being transferred, and a primary coil for the initial, or source, circuit.

Big industrial transformers, which reduce the voltage from overhead transmission lines usually several hundred thousand volts to the few hundred volts usually needed for residential usage, are something you may have seen on telegraph poles.

Diodes

A piece of semiconductor material, often silicon, that has been doped to produce a P-N junction is used to make a diode. Materials are doped to produce an excess of holes (positive charge carriers) on the P-side, or anode, and an excess of electrons (negative charge carriers) on the N-side, or cathode. Current flows from the anode to the cathode when a voltage is supplied across the diode, but not the other way around. With a forward voltage drop of about 0.7 volts, the silicon diode is the most widely used kind of diode. This indicates that when the voltage across the diode rises above 0.7 volts, the diode will begin to conduct current.

Typical diode types include the following:

Zener diodes:

When a certain reverse voltage, known as the Zener voltage, is attained, Zener diodes a unique kind of diode can conduct current in the opposite way.

 Light-emitting diodes:

Diodes that emit light when current passes through them are known as light-emitting diodes or LEDs.

 Schottky diodes: Schottky diodes outperform silicon diodes in terms of switching speed and forward voltage drop, with a typical value of 0.2 to 0.3 volts.

Diodes are used in many different electronic circuit applications. Typical applications include the following:

• Rectification
• Signal modulation and demodulation
• Light emission
• Voltage regulation

Transistors

A transistor is a device that has the ability to switch or magnify electrical power and electronic impulses. It controls the passage of current within a circuit by acting as a gatekeeper. Semiconductor materials with special electrical properties, like silicon or germanium, are used by manufacturers to create transistors.

Transistors come in a variety of forms, such as field-effect transistors (FETs) and bi-polar junction transistors (BJTs). Every variety has benefits and uses of its own. BJTs are frequently used in switches and amplifiers, but FETs are frequently used in integrated circuits and digital circuits.

There are several uses for transistors in electronic circuits. Typical applications include the following:

• Amplification
• Regulation of voltage
• Oscillations

Transistors come in different packages such as:

• TO-92 has dimensions of 4.58mm×4.58mm
• TO-18 has dimensions 12.7mm×2.97mm pitch
• TO-220 has dimensions of 9.2mm ×9.9mm
• SOT-23 has dimensions of 2.9mm×2.4mm

Considerations when selecting PCB components:

To guarantee optimum performance and dependability, engineers and designers must take into account a number of aspects while choosing PCB components for a particular application.

Electrical characteristics: Electrical characteristics including frequency response, voltage ratings, and current-carrying capability are essential for assessing if a component is appropriate for a particular circuit.

Thermal factors: Thermal factors are important, particularly in high-power applications where components must withstand high temperatures. To avoid overheating and preserve long-term operating stability, it is crucial to select components with the right thermal properties and heat dissipation capabilities.

Mechanical dimensions: Form factors and mechanical dimensions are equally significant, especially in applications that need to work with existing enclosures and mounting arrangements or in designs with limited space.

 Environmental elements: Environmental elements that can affect PCB component performance and durability include humidity, temperature fluctuations, and exposure to chemicals or pollutants.

Cost factors: Last but not least, cost factors are important when choosing PCB components because they have a direct impact on the total bill of materials (BOM) and production costs.

How can one buy components for PCBs?

You have to choose what you want to buy. You should consider the component’s appearance, model, functionality, and other important aspects before making a purchase of electronic parts. Look for a website that is honest, open, and straightforward

By initially using the search function to look for “component sample retail” websites (or small batches), you can find several websites that are sample-focused. While some websites will show the price prominently, others won’t. If the price is already stated on the website, that is the most sensible course of action. There’s usually no fee involved. You will need to contact the pricing via phone or email with each individual. All information, including the website’s URL, needs to be written down for later use, preferably in a larger

Delivery and Payment

The component’s model and type have been identified. Once the supplier assessment is finished, you can make a direct purchase. After the supplier verifies the order, it will be sent.

Examination

Things should be reviewed as soon as they come; the model should be examined first, then the amount. When there are limited possibilities for buying, there usually isn’t anything wrong. Critical parameters are then tested via spot checks. Please get in touch with the supplier right away if there is a problem so they can fix it or replace it.

Read More: Surface Mount Technology (SMT) vs Through-Hole (THT): Explained

Conclusion:

Circuit board component understanding is most important for outputs, soldering and cost-efficient purposes. Additionally, this helps to build circuits that are more dependable and efficient, which enhances the functionality and lifespan of the everyday items we use.

Looking for expert advice or a service provider for components sourcing?

Rush PCB UK has more than 15+ years of experience in circuit board manufacturing and assembly services. Get in touch with our team for any questions or an instant quote from our expert sales engineers at sales@rushpcb.co.uk or call us on +44 20 3750 0201

In-Circuit vs. Functional Testing: Pros, Cons, and Practical Applications

Using various PCB testing and inspection processes becomes essential when designing a Printed Circuit Board Assembly (PCBA) with few or no faults. Testing processes help eliminate all small flaws, enhancing the quality of both the PCBA and the final product. Consequently, PCBA testing aids in lowering production expenses.

Numerous testing methods can be applied in this way. Manufacturing defect analyzers, in-circuit, boundary-scan, and functional testing are a few of them. In-circuit and functional testing approaches are the most frequently employed.

 The process of evaluating individual circuits or components on a printed circuit board (PCB) prior to their assembly into a finished product is known as in-circuit testing or ICT. ICT makes use of a unique tool known as a “bed of nails,” which is a board with hundreds of probes attached to it that are connected to particular locations on the PCB.

ICT can identify errors like shorts, openings, erroneous values, or misaligned component orientations by delivering electrical impulses and monitoring the responses. ICT is quick, precise, and dependable, but it also necessitates a costly and time-consuming specially designed bed of nails for every PCB design.

A technique for evaluating the functionality and performance of a final product that includes one or more semiconductor devices is called functional testing, or FT. FT uses a test fixture that replicates the temperature, voltage, frequency, load, and input/output signals of the real-world environment and conditions the product will operate under.

FT is able to confirm that the product satisfies the customer’s specifications and expectations by comparing the actual output with the expected output. Although FT is extensive, flexible, and adaptive, its effectiveness also depends on the test software and fixture quality, which can be complicated and error-prone.

Advantages of In-Circuit Testing Vs. Functional Testing

 ICT is excellent at:

• Identifying production flaws such open connections, solder shorts, missing or incorrect components, and so on.
• Conducting a large number of tests without providing power to the device under test (DUT), so averting the majority of situations that might harm an assembly.
• Minimizing the amount of work required to program tests because all that is required is the concatenation of software component models and the bed-of-nails (BON) fixture-based switching of test instruments onto each component.

 ICT flaws include:

• Because each electrical node in the circuit requires an electrical connection, test fixtures are typically costly. Hundreds of pogo pins, or spring action pins, are frequently required. 
• ICT typically does not test continuity through connectors; hence connector errors are frequently missed. By applying stimuli, a functional test (FCT) confirms that a PCB assembly operates as intended by verifying the response and stimulating the PCB assembly.

 Functional tests aim to ensure that the circuitry operates as intended. Typically, testing is conducted “at speed” using DUT connectors and/or BON fixtures; a functional test fixture requires a significantly smaller number of pogo pins than an ICT fixture. Functional tests are particularly good at identifying functional defects within printed circuit board assemblies, assessing functionality while applying a range of input stimuli, amplitudes, or currents, and determining DUT power consumption during operation.

 FCT is excellent at:

• Finding functional flaws in an assembled printed circuit board
• Evaluating the assembly by applying marginal power supply’s voltage and/or current
• Evaluating the DUT’s performance while applying a variety of input stimuli, such as currents or amplitudes

Analyzing the power usage of the DUT while it is operating and identifying analog circuitry issues like:

• The oscillator frequency is off.
• Distortion or clipping of analog signals
• Problems with bandwidth or amplifier gain
• Power output circuit drive currents
• Problems with potentiometer adjustment
• Highlighting problems with digital circuitry like:
• Timing of signals (connected to design or components)
• Issues with communication (Ethernet, Device Net, Serial, etc.)

Some of the drawbacks of FCT include:

• Using high-speed instrumentation to characterize signals from the DUT is a common practice in FCT, but this comes at a higher cost than ICT because it requires a thorough understanding of the DUT’s performance; however, graphical programming greatly lowers this cost. 
• Lastly, testing through connectors can lead to reliability issues as they wear, but Bloomy mitigates this with sacrificial interposer cables.

Applications of In-Circuit Testing Vs. Functional Testing

 ICT tests individual components at different places using an electrical probe. ICT looks for resistance, capacitance, openings, short circuits, and other issues. Any disparities will be flagged by the test. Typically, in-circuit tests are carried out in two stages: with and without electricity.

/*Now this article will introduce a few of the flaws that ICT can detect in this part.

• Component marks, solder bridges, short circuits, shorts between component leads and traces, problems with soldering and the process itself
• Lead distance, component distances, land areas, and component dimensions
• Values of resistors in the circuit
• Accurate placement or configuration of jumpers or switches
• Presence or absence of passive elements
• The existence or lack of active analog components; analog component misorientation
• Digital element misorientation
• Values of capacitance and inductance
• Incorrect or absent parts

Applications of  Functional Testing

Applications for PCB functional testing are many and span nearly every sector of the economy that uses electronic components. Here are thorough explanations of a few common functional testing application domains.

1. Electronics for consumers

 Functional testing guarantees the accuracy of features including high-speed data transfer, power management, and circuit board display drivers, improving user experience in consumer electronics like smartphones, tablets, and smart home appliances.

2. The communications sector

 Functional testing is an essential phase to confirm critical indicators including signal processing, data interchange, and RF performance, assuring the stability and reliability of communication systems. This applies to base stations, routers, and satellite communications equipment.

3. Electronics for automobiles

Functional testing is crucial to ensuring the electronic modules in car navigation, entertainment, and support systems operate steadily in complicated environments, which is directly related to driving safety.

4. Medical supplies

 The foundation for patient safety and effective treatment is extremely accurate signal acquisition, processing, and control functions, which are ensured by PCB functional testing of medical devices, which includes ventilators and EKG machines.

5. Aircraft

The highest level of accuracy and thoroughness in functional testing is required in avionics, satellite, and missile guidance systems, assuring stability and dependability in harsh conditions with no room for error.

6. Defense and military

Functional testing is crucial to assure equipment camouflage, anti-interference, and immediate reaction in military applications such as radar systems, communications equipment, and navigation equipment. This is directly tied to national security.

 7. Automation and control in industry

Functional testing guarantees accurate control and effective control system functioning in industrial robots, automated production lines, intelligent sensors, and other applications, enhancing both production efficiency and safety.

 8. Electricity and new energy

 Functional tests verify the stability and effectiveness of circuit boards under high voltage and high current situations in solar inverters, electric car battery management systems, and smart grid equipment, propelling the advancement of clean energy technology.

 Conclusion

Electronic product quality and dependability are greatly enhanced by in-circuit testing, or ICT. By offering a thorough method for identifying and treating flaws early on, it keeps faulty parts out of the hands of consumers. ICT is becoming a vital tool in contemporary engineering due to improvements in test capabilities, automated integration, and creative software solutions.

In the electronic manufacturing industry, PCB functional testing is also a vital link in the chain that influences not only the innovation and growth of the sector as a whole, but also the performance of individual products. Any industry that uses PCBS, such as consumer electronics, communications equipment, aircraft, and medical equipment, cannot exist without functional testing. Future developments in the field of PCB functional testing will see a significant focus on ongoing test technology optimization and test automation advancement in response to growing market demand and complexity.

 Rushpcb UK provides various testing options which also include ICT & functional testing once PCB is manufactured & assembled. Do reach out to our sales engineers for your upcoming project at sales@rushpcb.co.uk or call us at +44 20 3750 0201.