A PCB offers mechanical support and connects electronic components electrically using conductive tracks and several other features etched from copper sheets illuminated onto non-conductive substrates. PCBs are assembly and design defines the type of final PCB product; that is, single sided PCB, double sided PCB or multilayer PCB. Modern PCB assembly processes are extremely complex and automated thus high speed which might lead to component failures. This is due to lack of sufficient understanding of the concept of design for assembly (DFA). Manufacturing and assembly should be considered during the design stage of every PCB. We are professionals in PCB design, assembly and manufacturing. Please join us as we discuss the various methods of assembling your PCB and the relative advantages of each method. To learn more about PCBs, PCB outsourcing and manufacturing, you can visit our blog https://www.rushpcb.co.uk/blog/. However, as already stated, in this article we shall only discuss the PCB assembly methods.
To begin with, the first critical process this occurs before PCBs are manufactured is contacting the assembly house or company and discussing your project with them. Communication is crucial throughout the product’s life and the 2 parties should participate relevantly. Uniquely, its house has its own strengths, methods and requirements and as their customer, you should be familiar with them before outsourcing their assembly services. Some of the important components needed for PCB assembly are:
- Printed Circuit Boards
- Electronic components
- Soldering materials-solder wire, paste and solder bar.
- Soldering flux
- Soldering equipment like soldering station and SMT equipment
On the other hand, before submitting the PCB for assembly, there are some tools that you should provide to the PCB assembler. These items include the BOM (Bill of Materials) which should categorically state the parts numbers, description, reference, value, package type and number. Please always ensure that this information is accurate and each detail that you would wish included in the PCB is included to avoid assembling a PCB that doesn’t meet your specifications. However, after detecting confusion or a missing part, most PCB assemblers will stop the process and seek for clarifications. This can lead to late delivery of your final PCB. Sequentially, the centroid or X-Y rotation side (XYRS) file is required since it clarifies the rotational angle, X and Y coordinates and the side of the board each of the parts is placed. Computer-aided design programs used for the PCB design process can export any XYRS file directly and those that cannot have an extension that gives them the capability. As if that is not enough, you should also provide the Gerber files for the PCB.
After receiving the requisite information, the PCB assembly company will review what you send and rectify the obvious errors before getting back to you for clarification. Some of the above files and processes are automated in software and machines in most of the companies thus the process is not much complicated. The initial physical assembly begins with the setting up of the pick and place machines by loading the XYRS files and various parts to be used in the machine. However, some assemblers populate a board manually but scan it into the pick and place machines for proper component placement. This might take longer and it can lead to large setup costs of the Printed Circuit Boards. Pick and place machines can only place parts on one side of the board and then they are ejected, soldered and then run through the pick and place process to take care of the back side. The sequential procedures that follow this process are soldering, testing and shipping.
PCB assembly with thru-hole electronic components
Electronic components with leads coming out inserted through tiny holes in a PCB for soldering are known as thru-hole electronic components. The assembly process for these components when used in PCBs requires the use of hand soldering and wave soldering. Moreover, the temperature range used in this process depends on the solder type used. In these soldering processes, the solder is usually in the form of solder bar and it is put in a high-temperature bath. Moreover, the PCB with all its thru-hole components in holes is the passed over the molten solder using a conveyor belt. The soldering process involves the following procedures: inserting the electronic components in the molten solder, flux application, cleaning and testing. However, sometimes hand soldering is carried out in assembling companies with less with little work load or in repair work. However, a quality soldering station or solder wires and flux are use in this process.
PCB assembly using Surface Mount Technology
The SMT (Surface Mount Technology) is a PCB assembly process for SMD electronic components. Unlike thru-hole components, SMDs don’t have legs or leads but they are instead mounted on the surface of a PCB. The electronic components and soldering materials used in this process are also different from those used in the thru-hole soldering process.Surface mount parts are held in place by the tension of the solder paste which is allowed to be flow continuously. This is in a bid to prepare them for the process of wave soldering. On the other hand, as the pieces are placed on the PCB, there is a literal push as the pick and place inserts them in the board. The downward pressure acting on the board can cause board flex in panels with bare minimum connecting tabs between the boards. As the pick and place moves away, the board snaps to its original position and sometimes this might flick pieces off the board.
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