One prototype is never enough, and here's why
This is a question I occasionally get, and the people who ask it are almost always people who don’t build prototypes themselves. That’s because the people who do build prototypes themselves know better than to trust certain things.
Whenever I had an assembly board made, I always arranged for one extra bare board (a board with no parts mounted) to be sent along. This let me check the quality of the bare board myself, separately from the assembly process. On one occasion, an entire inner-layer circuit of a multilayer board was missing. The cause was a data mix-up between the board manufacturers.
It’s an embarrassing story, but before I caught it, I wasted about two days: mounting parts on the board, powering it on, checking various waveforms, finding the power supply not working, and probing point by point to trace the fault. In the end, I stripped every part off the board to get it back to bare, and by checking continuity at each point, I finally found the problem described above.
“If only I’d had a separate bare board, I would have known instantly,” I thought, my shoulders dropping.
<Sometimes trusting the assembly shop, sometimes not>
Prototype boards occasionally warp. A PCB is a mille-feuille of multiple materials, so naturally the thermal expansion rate differs by layer, and careless heating or cooling can bend it.
Some of you might say, “I’ve never seen that happen.” That just means you’ve been lucky in your surroundings.
Several factors determine whether warping occurs — roughly speaking, board size and temperature — but in practice you can’t be sure until you actually try it. So a skilled assembly shop tests this in advance. They arrange extra bare boards, prepare spare parts too, and run trials beforehand to check the assembly condition. If the board does warp, it causes all sorts of problems that aren’t obvious at a glance, such as poor solder contact or damage to small components. Avoiding this kind of trouble is thanks to the efforts of people behind the scenes, like the assembly shop.
However, this kind of care is something shops do purely as their own risk hedge, and it’s almost never listed on the “menu” of services. So laying the proper groundwork yourself is what you might call a developer’s skill.
The bare board has no trouble at all, the assembly proceeds without a hitch, and yet it doesn’t work. That happens. In fact, it happens all the time. It turns out the design was wrong, but as a small mercy, it’s a spot that can be fixed well enough by hand. Let’s modify it. On your one precious board?
Keeping spares on hand so that this doesn’t happen is what makes a good engineer. Just in case, I had made three boards, so even after breaking one, I still succeeded in modifying the remaining two. Once the basic operation checks were done, I moved on to firmware development, but the schedule turned out to be tight because the modification work had eaten into the timeline. I decided to bring in another team member to help.
Since there were two boards, the two of us split the work without any trouble.
Development is like this in every respect. Anyone who tries to get through with a single prototype unit isn’t someone with exceptional confidence in their skills — they can be safely judged to be simply an inexperienced amateur.
The content of this post is an excerpt (original text) from the following book. If you’re interested, please consider getting the book.
The Shape of a Happy IoT Startup
The Shape of a Happy IoT Startup
Originally published in Japanese at https://clazytech.com/2022/09/1155/. Translated with LLM assistance and reviewed before publication.