When designing a Printed Circuit Board Assembly or PCBA, various factors such as thermal management, signal integrity, component placement, manufacturability, and cost control all must be taken into account. Those engineers who tackle those challenges early on - with careful design, simulation, and working closely with manufacturers - can prevent costly redesigns, and have a reliable, performance-driven electronic product.
No matter if you are using any electronic device, such as a smartphone or industrial controllers, they all require printed circuit board assembly (PCBA) to work. Creating a perfect PCBA the first time is a challenge! Engineers have to balance the electrical performance, physical limits, manufacturing requirements and budget with short product development schedules.
If you get it wrong, it can cost you more than just rework - it can be the entire board. Do it right, and you've got a solid platform for a stable, scalable product.
1. Why is thermal management important in the design of a PCBA?
Heat is among the leading causes of electronic unreliability. Heat dissipation is more of a challenge, rather than an easy task, as components continue to become smaller and power densities higher. Without effective thermal management, components can degrade, their lifespan is shortened and, in extreme cases, catastrophic board failure can occur.
These high-power devices, such as voltage regulators, processors and power amplifiers, produce high levels of heat when they are working. If it is not properly planned, that heat can be focused in certain areas, resulting in hot spots which put pressure on adjacent components and solder joints.
Engineers need to tackle thermal challenges by:
· Thermal via connections for moving heat from a hot part to a heat sink or heat ground plane
· Choosing the correct PCB material for the application with a right thermal conductivity value
· If possible, keep heat-generating items spaced out from each other so as to prevent "heat clumping"
· Early simulation of thermal properties instead of problems during prototyping stage
2. How is signal integrity achieved on today's PCBs?
Signal integrity challenges are getting tougher with the rising clock speed and data rates. Signal integrity problems such as crosstalk, EMI and mismatched impedances can cause noise, data errors, or even complete loss of signal.
Traces that are long, complex, or close to other signal paths are especially sensitive to high speed digital signals. Performance can be affected by any design detail, such as routing a high speed trace too near to a noisy power line.
Common methods for signal integrity protection are:
· Controlled Impedance routing determined by the width of the trace, thickness of the copper and properties of the dielectric material
· High speed signals routed in pairs to eliminate noise
· Ground planes strategically positioned to protect vulnerable traces
· Minimizing via usage on critical high-speed paths - each via is an impedance discontinuity
3. So why is it so tough to place components on dense PCBAs?
The need for a smaller footprint with no reduction in functionality for modern electronics puts a tremendous strain on component placement. Space requirements for each component must be adequate to ensure good soldering, thermal dissipation, and mechanical clearance, but space continues to become a concern on the board.
The problems with the components placement are compounded by the downstream issues of difficult routing, thermal hot spots, mechanical stress points and manufacturing assembly errors. The early stages of placement have an effect on all the subsequent stages.
In order to best overcome this challenge, engineers should:
· Trace lengths and signal delay will also be shortened and reduced by grouping related components together logically
· Ensure that high power parts are kept away from heat sensitive parts such as electrolytic capacitors
· Allow sufficient space around connectors and mechanical installation sites
· Think about the assembly process itself – placement which might be efficient to film would be difficult to reliably assemble by a pick and place machine
4. How to make PCBAs more easily manufactured?
The ideal design on screen can turn into a nightmare on the production line. Design for Manufacturability (DFM) is a process that can be tricky even for the seasoned engineer – it involves designing boards that can be manufactured reliably and economically in large quantities.
Typical DFM problems are parts placed too close together to be assembled on a machine, variations in hole size which make drilling difficult, and insufficient clearance between pads that cause solder bridging during reflow.
The key to lowering manufacturing friction is getting manufacturing partners involved from the start. Engineers should:
· Apply manufacturer's trace width, spacing and via size requirements before laying out designs
· Where possible, standardize component footprints and hole sizes
· Do not place any components too near to edges of the board; mechanical forces at depanelization can damage the components
· Perform a DFM check before committing to fabrication, prevent problems at an affordable cost
One of the most frequent (and expensive) PCBA design errors is not performing a DFM (Design for Manufacturing) review. One missed clearance problem can cause weeks of production delays and run up costs.
5. What are the various methods for measuring the performance of a PCBA?
Each design decision involves a cost and engineers always have to balance against the budget. The quality of the materials used, the tolerances used and the number of board layers can be increased to increase the performance of the product, but at the same time the cost increases and sometimes becomes too much for the product's market position.
In the high volume production, the cost pressures get greater and greater, and even the minor savings per unit will add up to large amounts. Meanwhile, by cutting corners to save money, you can also present reliability risks that come with warranty claims and lost reputation at a much higher cost.
Engineers can control this balance by:
· Using minimum layer thickness required for electrical needs, not just for convenience;
· Using standard component packages – taking advantage of volume pricing and availability
· Considering TCO instead of unit price, including yield rates and failure costs
· Engaging with the manufacturer at the beginning of the design process to understand how decisions are made to influence scale cost
Conclusion
Thermal management, signal integrity, component placement, manufacturability and cost control are not stand-alone problems. These are related decisions that influence each other during the design process. A modification to address a thermal problem could become a routing problem; a manufacturing material change could become a manufacturability issue.
The winning engineers at PCBA design consider these five challenges as a system, not a checklist. They model early, discuss with manufacturing partners before deciding on layouts, and make intentional compromise decisions to meet actual demands of the product, instead of going with the path of least resistance.
Begin your next project in the world of PCBA by identifying these five challenge areas and matching them up to your products' requirements. Discuss your application with your manufacturing partner before you lock in your layout, and determine which of the following trade-offs are relevant to your application.
If you are looking for a fine PCBA provider, look no further than Optima Technology.
