If you’re like most people, you probably dread going to the DMV. It seems inevitable that no matter what time you go, you end up waiting in line for several hours. And there’s a chance that even after you finally reach the front of the line, you might be informed that you need a different document than the one listed online and the cycle begins again. Sometimes, getting a PCB manufactured can feel the same way. You design a nice board that does everything you want it to, and then your CM informs you that it’s impossible to manufacture and assemble. That’s why it’s important to think about PCBA process optimization from the beginning. The first step in PCBA optimization is to look at material and component selection. Once those wrinkles have been smoothed out, you can focus on increasing efficiency in the design stage. Last but not least, you’ll need to work with your CM to prepare your board for assembly. By diligently following all of these steps, you can maximize the efficiency of your PCBA design and development process.
Optimize PCB Material and Component Selection
One of the first things you should consider before you even begin designing is how to optimize the selection of your materials and components. Keep in mind that if your materials are exotic enough, you may not be able to use any run-of-the-mill CM and might have to find one that can work with your specific requirements.
PCB Material Selection
FR4 used to be the default substrate for the vast majority of PCBs. Now, as boards become increasingly complex, many designers have to consider alternatives. The following list will give some insight into considerations for PCB materials:
- High Speed: When you’re designing a high-speed circuit, material selection is of critical importance. Different insulators have a variety of dielectric constants which affects the decay of high-frequency signals. Depending on the frequency copper roughness may also be a factor. The skin depth effect can effectively lengthen traces at high frequencies. This can lead to mismatched impedances and increase loss.
- Physical: Even electrical designers have to think like mechanical engineers at times. One of the more common physical failures stems from vibration. This can cause cracked solder joints, broken traces, and more. The board substrate, mounting material, standoffs, etc., will all affect what kind of physical shock your PCB can handle. Simulating board vibration can give you a good idea of how different materials will hold up.
- Thermal: Some circuit boards have to operate in high-heat environments or places where the temperature often swings between hot and cold. Large temperature differentials cause your board and components to expand and contract and can break a PCB apart over time. Check each material’s coefficient of thermal expansion (CTE) to see how much they will expand and contract during use. You may also want to estimate your board’s thermal resistance to see how the heat will distribute across it.
- Standards: Depending on where your PCB is being deployed or sold, you may have to abide by certain standards like RoHS. RoHS specifies lead-free solder, which takes a higher temperature to melt than leaded solders. Some industries may also desire halogen-free circuit boards. This can require new solders or substrate materials that have not been proven throughout the years.
- CM Check: Before you finalize your material selection, check to make sure your CM can actually make a board with the specified substances. Waiting in line at the DMV to renew your license and having to return with the right documents is one thing. Errors in PCB development are much harder to fix and vastly more expensive. Imagine the time and money you’d waste if you worked hard on a halogen-free PCB design before consulting your CM, only to discover they don’t have the capabilities to create your board!
PCB Component Selection
After you have all your materials lined up it’s time to take a look at the parts list. This part is more straightforward but still requires future planning. Things like physical shock and thermal environment matter for components as well as materials. In general through-hole components will deal better with vibrations and high power or heat, whereas SMT parts can be less expensive to buy and assemble.
Once the question of through-hole or SMT has been answered, you’ll need to think about the BOM in the long term. You may want a board to be manufactured for ten years, yet a critical part will only be available for the next five. Communicate with your CM to make sure all the parts you need are available. Once you’ve confirmed your supply, make sure to accurately represent all components on the BOM. An incomplete part number or incorrect quantity for a part can result in incomplete PCBAs and expensive reworks.
A good rule of thumb during the material and part selection process is to frequently check in with your CM. Otherwise, you may find out they can’t make your board in the end or have to make expensive last-minute changes.
Optimize PCB Design and Assembly
Once you have all your parts and materials selected, it’s time to move fully into the design phase. At this stage, it’s important to design your board to be fabricated and assembled with ease. The following table contains some DFM and DFA suggestions to help you optimize your PCBA process:
|Differential Pair Routing||Keep traces close together and match their length.|
|Mixed Signal Design||Keep them separated and ground carefully.|
|Creepage and Clearance||Materials matter and grooves can be added to increase creepage distance.|
|Controlled Impedance||Use uniform materials, route traces over a copper layer, and coordinate with your CM.|
|Footprint and Orientation||Make sure your component footprints are correct and their orientation is clear for your CM.|
|Drill Holes||Check hole sizes for NPTHs and PTHs and watch the aspect ratio.|
|Edge Clearance||Check with CM for scoring or routing clearances.|
|Thermal Reliefs||These can reduce assembly defects.|
|Panelization||Confirm edge clearances and clearly mark orientation with fiducials.|
This is not an exhaustive list, so you should also upload your CM’s design rule check (DRC) files to your design software. DFM rule checks should be performed multiple times during the design process: after stackup, after part placement, after routing, and after labeling. Following your CM’s DFM rules will make the entire process much more straightforward.
PCBA process optimization starts at the very beginning of the PCB development process. As you select materials and components, you should always be thinking about overall process efficiency. When moving into the design phase, you should keep abreast of your CM’s DFM rules and check your design multiple times to make sure every part is in its rightful place.
|Tempo's Custom PCB Manufacturing Service
One of the most important parts of optimization is choosing a CM that will help you throughout the entire process. That’s something we specialize in here at Tempo Automation.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on PCBA process optimization or how to maximize the overall efficiency of your PCB development process, contact us.