From Design to Manufacturing: A Journey in Electronics Production
“Design is overrated, Manufacturing is underrated”
Though I might not agree with the first part of the statement, I definitely do agree with the second part. In this article, I would be talking about my learnings from transition from design world to manufacturing world for electronics products. I'll also cover importance of invoking design for manufacturability, testability and assembly failing which might drastically affect cost or performance of the product. Finally, I'll be taking few specific examples from my recent project. Also, it was amusing to relate the issues directly with first principles of physics.
The Background
To provide some background, for those who don't know me, I've been working in various stages of product development for about 7 years now. Till a couple of years back, the firm where I work had been outsourcing manufacturing of our designs to various 3rd party vendors who would do PCB fabrication, PCB assembly, enclosure manufacturing, cable harness manufacturing etc for us and then we made strategic decisions to invest and slowly bring some of these capabilities in house. Starting with CNC machining, cable harness, PCB assembly and a few other processes.
Recently I transitioned from designing products to managing inhouse manufacturing for a product. The first product was a power electronics evaluation kit, mostly containing few PCBs, some cable assembly, heatsinks, enclosure and such. We got to manufacturing and slowly the behemoth of manufacturing variables started appearing. Variables to which as a designer I had seldom paid attention to. Many of them are small but if not taken care would severely affect the manufacturability or performance of design. To be fair, the product was decently well designed, although when it comes to manufacturing, small parameters which designers might not even be aware about plays a big role. Design for manufacturability, design of testability, design for assembly are more often than not ignored, especially if the manufacturing volumes are not huge, but small decisions can severely affect the performance, ease and cost of product.
Case Studies
Let's take few examples, some of these are specific to power electronics but similar variables would be applicable for other designs as well
PCB Warpage
The first issue we observed was PCB warpage. One side of PCB was getting bent and creating a warpage of 150 microns. Now, I know it sounds small, but to put things in perspective, average solder paste thickness is just xxx micron, that means long components like PCIe connector would not lay flat on surface and middle pins would not even touch solder paste. The root cause, copper imbalance between layers combined with high copper thickness (4 ounce). This causes board to heat unevenly, causing uneven thermal expansion finally causing PCB to bend just like a bimetallic strip.
Solder Bridges
Second issue, this was caught and avoided early on. Solder joints between pins. Root cause, higher stencil thickness or higher stencil apperture opening based on thickness. Stencil thickness and apperture area finally determines the amount of solder paste that will be deposited at a pad. Have a bit more solder paste than required and it'll overflow to nearby pad and form a joint during reflow effectively shorting the pins.
Temperature Exposure
Another potential issue, although this wouldn't cause manufacturing problems but would result in degradation on product performance and reliability if not taken care during manufacturing is the reflow temperature. Usually reflow temperature in manufacturing is dictated by the metal composition in solder paste used. During design, the designers might be unaware about the temperatures and duration for which the parts on the board will be exposed to. Every semiconductor part has a recommended reflow temperature and duration beyond which part performance would be affected. As a part of the previous project for a semiconductor firm, we performed studies correlating device performance of high precision clocks by the effect which multiple reflow cycles has on the design. This is where right integration of manufacturing and design comes into play since each team is generally not aware or concerned about the parameter consideration by other team and might cause negative impact on product performance.
Solder Paste Selection
Few critical designs like power or high speed would even call for careful consideration of Solder paste or flux to be used. Water soluble flux are generally preferable for high speed designs and needs to be properly cleaned off after manufacturing else could cause issues with PLL locking specially for high precision clocks. Whereas no clean flux would be preferred for other designs as they leave less residue and reduces cleaning step needed during assembly.
Conclusion and Resources
I had fun learning and correlating these seemingly small and numerous variables then correlating them with issues observed or forecasted. As a engineer or project managers managing variables is all we do and understanding variables and constraints from different domains would make the final product better.
To highlight some gorgeous resources, huge shout-out to below resources detailing fabrication and assembly steps and processes in detail.
Interested in learning more about the PCB Fabrication process? I came across this awesome detailed video
How about common assembly issues?
Also the below blog is rich with manufacturing resources
I hope this article was as interesting for you as it was for me learning these parameters.
Until next time. Signing off.