10 Tips To Help You Choose A PCB Design Vendor
The sassy and coming of age PCB that you just put forwarded in the market suddenly hit the bottom rocks? Even after using all the new age technologies, still not utmost cost-effective, performance is not optimized to the optimum level? Are you choosing the right people? The correct PCB design vendor?
No matter how advanced the PCB manufacturing or assembly process you adopt, you can still have the same persisting issues. It is learned in a very hard way that business and engineering is a heterogeneous mixture. Yes! Somewhat like oil and water. The reason is not the difference in intensions but in perspective.
Hence, I will take you through some points that you require to keep in mind before you approach a PCB design vendor, then no matter if you hail from science or business.
Today’s products can be quite complex to design, hence focus falls upon the more “interesting” aspects of the product, like the FPGAs or MCUs. But the fact is unless the board is designed correctly in the first place, you are going to run into issues sooner or later. It is also very important for you to know whether the PCB design vendor you have chosen is adequately equipped to design your board. Particularly a few details should be discussed extensively before you can zero down upon the design.
PCB stack-up: this becomes quite a trade-off between fabrication processes and layer count to achieve the desired reliability, yield, and cost targets.
Via types: This is also an aspect that is quite important, if your design vendors use too many types of vias in a single PCB, alert, alert! The best design will have a minimum of the different types of vias.
Are the via aspect ratios correct? Make a note to a high of an aspect ratio can really pull down the reliability of PTH boards. In that case, the use of microvias is the best option. Also, it reduces the length of the traces, hence making better signal integrity. And what about the component placement, crosstalk budgets, layer allocation?
It is very important to know if your designer has a DFM team. This will ensure the finished design can actually be manufactured.
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The breakout strategy of a board is also quite an indispensable part of designing. Your designer must first ensure you can breakout and route all of the signals on high-pin-count devices. When you breakout, you basically apply a fanout solution. You route traces from those fanouts to the perimeter of the device prior to the general routing of the PCB. This will also affect the stack-up plan.
In today’s miniature era, maintain strong signal integrity and power integrity has become quite a hustle. Though usually an engineer is supposed to take into account aspects such as the signal rise and fall times, track lengths and characteristic impedances, and the drive strength and slew rates of the drivers and terminations. But to ensure the best of performance signal integrity simulations on the PCB should be performed both pre and post layout.
Again, for power integrity, both the DC and AC performance of the power distribution network is of vital importance.
PCB designers are persistently put to test, addressing the issues of shrinking electronic items through engineering boards with the most efficient positioning of components. That is expected to do the necessary functionality while meeting the specifications of the item to contain the board. Therefore, ensure your PCB designer has time-proven constraint templates available. Sizing and placement of critical elements, including minimum and maximum tolerances, electrical demands including power needs, and impedance factors, required components, all combine to generate a primary set of constraints for the PCB design. This can shapeup the design of new boards or upgrades to existing PCBs with considerably very fewer errors.
Another very important point is the materials and components. Sometimes, we think they are fabricators headache and hence, do not enquire about the designers about the materials. Consider during the layout phase the materials and components you have in mind for your board. Ensure your PCB designer has chosen the optimal materials and components for your board, and also the role the designed board plays to those items’ strengths.
Let me share something interesting with you all before we get started. It is about an aerospace PCB batch. It was reported that the PCBs had some issues, shorting issues to be precise. But the PCB batch passed the electrical test with flying colors. All the PCB experts were quite distressed, no matter what they did the fault seemed to come back. And not to forget aerospace is one of the most delicate applications of PCBs, reliability being one the key factors.
So, where did it go wrong? Was it the specs, or the placement of the components? Or manufacturing? Maybe the assembly was at fault? This went on for almost a year.
Finally, it was discovered the problem was CTE, aka the coefficient of thermal expansion. The material used as the base was a type of FR4 and the chip carrier was of ceramic. So where is the problem? First understand what CTE is. It is nothing but a characteristic thermomechanical property of a material or a composite. It is the tendency of a material to expand as it is heated. The CTE of any conventional PCB is 17-18 ppm/°C and of a ceramic chip carrier is 6 ppm/°C. So, when a ceramic chip is mounted on a conventional PCB, the mismatch in expansion can or rather will cause shear stress among the solder joints. After a few thermal cycles, it will lead to the hardening of the joints and ultimately cracking of the joints.
Another fundamental query of yours should be about the order of the component placement. Yes! It is one of the most critical design guidelines. The recommended order is connectors, then power circuits, then precision circuits, then critical circuits and then the rest of the elements.
Next on our list are the power, ground, and signal trace considerations. Track designs, pad and hole dimensions, etc., are very important and you must know about these factors before you lay your concept to the PCB design team.
Thermal issues can impact many different parts of the PCB design process.
Boards are getting smaller whereas the current passing through the traces is getting higher. The consequence? A high temperature and heat generation. Ensure your PCB design has sufficient space around all components that may get hot. The more heat they create, the more area they will need to cool off. Note the placement of the critical components not to place, they are not supposed to be near heat sources. Your board is multi-layered? Or may you have assemblies with high copper content? If so, you may need to include cooling fans, heat sinks, and thermal reliefs, which are critical for wave soldering.
Throughout the PCB design process, as well as the rest of the PCB manufacturing process, you should continuously check your work. Catching problems early on will help minimize their impact and reduce the costs of fixing them. Hence, look out for the testing, two common tests your design should go through are the electrical rules check and the design rules check.
Last but not least, if you choose a PCB vendor who has it all, it will actually cut down a lot of the above points. Well, some companies have an entire product development department, yes! You just approach them with your concept and they do the rest. Nonetheless, whoever you choose, make sure to have constant communication to make yourself and your concept heard, with a hint of business of course.