Rapid Prototyping

Prototyping High-Frequency PCBs: Techniques and Considerations

RUSHPCB has grown over the years and the quality of services and range of products increased substantially as well. However, with the fast advancement in technology and changes in customer demand patterns, prototyping of PCBs has become more hectic than it was some decades ago. This is because most of the electronic components have become smaller in size due to the introduction of the Integrated Circuit (IC) technology. Consequently, measures like illumination, observation and careful handling of the tiny IC component parts should be done carefully especially for high-frequency Printed Circuit Boards which have a wide range of application in the electronics world. These PCBs aid in meeting the increasing demand for miniaturization and utilization of high-frequency. To prototype any PCB, one needs tweezers, lamps, magnifiers, solder stations and microscopes. However, it is crucial to confirm the connections and assembly of the PCB before prototyping it to eliminate chances of errors and short-circuits. The prototyping of high-frequency (HF) PCBs shall be discussed in detail in this blog.

To begin with, in HF (high-frequency) PCBs, HF signals are reflected on the boards implying that the impedance or dynamic resistance varies with that of the source. To prevent these capacitive effects, all parameters are specified and implemented with high levels of process control. Comparatively, the impedance specified by the customer is checked by the design engineers for manufacturability and a calculation model selected depending on the number of layers needed, the PCB layout and the required impedance. With this, it is possible to adjust the PCB characteristics to operate at the needed frequency signals and all customer specifications are adhered to.

On the other hand, it is recommended that one uses a large area ground plane for precision purpose and high-frequency Printed Circuit Boards. This is because the components used in the design of these PCBs are different from that those used in the normal PCBs so that they can accommodate high-frequencies hence high efficiency of operation. The differentiation between high precision and high speed mixed signal circuits are difficult to manufacture thus careful prototyping is crucial.

Various types of PCB conductor finishing also provide different results due to conductor losses depending on the frequency of operation of the PCB. It is, therefore, crucial that high-frequency PCBs operated on low loss conductors like immersion gold and electroless-nickel so that the most of the electric fields lie between the copper layers and a significant current density is provided at all corners of the PCB. At low frequencies, the current can flow through the surface of the PCB leading to the skin-effect phenomenon hence radio-frequency interference. However, at high-frequencies, the skin depth is minimal (150 to 300 micro inches) hence most of the current densities are concentrated in the Nickel gold finish of the ENIG-plated conductors.

Different from that, in the fabrication of high-frequency PCBs, the parasitic capacitance, resistance and inductance should be minimized. The impedance of HF PCBs is affected by several factors like the dispersion of the PCB materials where the Dk value of the PCB is higher than that of low-frequencyPCBs. Dispersion is, therefore, minimized for higher quality and frequency Printed Circuit Boards.

Different from that, there is a prototyping technique used in conventional double-sided high-frequency Printed Circuit Boards using the conventional Computer Aided Design (CAD) techniques. This PC based software layout offers ease in the design and prototyping of the PCB and in coming up with the schematic captures to aid in the verification of the connections in the board to avoid short-circuits which can damage the components hence the PCB becomes faulty. However, for high-frequency PCBs, the analog traces and component placements should be done manually with all the design rules adhered to.  Luckily, one can also come up with a high-frequency PCB using a milling machine or an automatic drilling machine which produce either single or double-sided PCBs directly by milling or drilling holes to remove the conductive copper hence the creation of the required insulation paths thus the final prototype PCB is achieved.

As if that is not enough, a sufficient method to prototype HF PCBs is the dead-bug prototyping technique which the International Semiconductor Staff Scientists recommend. It is so called because the finished prototype resembles an insect lying on its back with the legs in the air. The technique uses a solid copper clad as its ground plane. The ground pins of the ICs are soldered directly to the plane and all the components wired above the plane. The circuit nodes are all suspended in the air hence the name “air-ball”. However, one main weakness of using this prototyping technique in high-frequency Printed Circuit Boards is that it is difficult to wire together fast circuits with controlled impedances.

Another HF PCBs prototyping technique is the wire wrapping which is mainly used in digital designs with fast signals. The process was developed by Copper Hand Tools and one needs to be cautious of undershoot problems on the clock. Moreover, for moderately sized boards, it is recommended that one buys a manual or an electric squeeze-wrap tool instead of using the spinning wraps with a cheap barrel tool. However, the expected results should not be much different no matter the prototyping technique one uses for the high-frequency Printed Circuit Boards.

We are professionals in Printed Circuit Board design, assembly, fabrication and prototyping. This is because we have state of the heart equipment to help us serve you at our best capacity. Moreover, our team of engineers works round the clock to ensure all your demands are met with the quality and uniqueness of your product being maintained. Do you have any question or would you like to get in touch with us? This is simple; you can visit us at www.rushpcb.co.uk and get to learn of the range of PCB products and services and products we offer. Comparatively, you can contact our sales representatives through 0203 750 0201 or sales@rushpcb.co.uk for any queries or clarifications. Serving you is our desire and pleasure. Please pay us a visit today.