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Powerful Prototypes: Cost Reduction in Design

Getting custom electronics manufactured is not cheap, fast, or easy. As the proverbial saying goes, “You can pick two of those three attributes and then go to lunch.” If you picked fast and easy, then you can have a peanut butter and jelly sandwich, or maybe just peanut butter.

I tend to simplify the proverb from three attributes down to two: people are either in the “more time than money” set or the “more money than time” set. Basically, being in the more money set can make life a lot easier, but it will cost you. That may sound a bit harsh, but it’s a continuum—not an absolute one way or the other.

It’s great to look on the internet and see a myriad of options for getting your amazing electronics product built, but at some point in your career, every one of those options is either going to seem too expensive or come with the risk of low production yields. Makers and those in early-stage startups often begin their journey without a lot of money, and that is right where this column sits.

Fortunately, there are ways to keep costs down and yields up without adding cost. Often, a simple but not necessarily obvious decision can have a rather large impact. With that in mind, here are six ways to keep costs down and yields up that you can do without a lot of effort.

1. Accept Longer Turn Times (Lead Times)

Lead times are one of the biggest factors in electronics manufacturing. Unfortunately, today’s fast-paced world tends to forget this factor. I can be sitting at my desk, get hungry, and through a quick online order system, have a sandwich delivered to me in about 15 minutes. Almost everything is at the tip of our fingers and rarely more than a day’s shipping away. That’s the world we live in today.

Some quick-turn electronics manufacturing houses can turn an assembly job around in a day or two, but it costs a lot of money to do that. If you need it, go for it, but if low-cost is important to you, slow down and pick a longer turn time. Maybe get a small number of prototypes quickly, so you can write your firmware but put the higher volumes on order with longer turn times. With fab houses, the most economical lead time (without getting ridiculous) point is often at around two to three weeks. For on-demand assembly houses, that point is usually three weeks.

You can also trade off lead time between fabrication and assembly. It may be less expensive to use a longer assembly turn time and a shorter fabrication turn time, or vice versa. Check it out to get your best value.

2. Avoid Leadless Packages Like QFNs and BGAs

This one is getting more difficult due to generalized shrinking component sizes, but if you don’t need the space savings that come with a small leadless part, find a larger version. QFNs and BGAs can get down in the 1–2 mm square range, and BGAs are starting to show up with pitches down to 0.3 mm or even 0.24 mm. That's great if you need those packages. However, since all of the leads are underneath, your assembly house will have to X-ray every part. That adds a bit of cost to the process, or you can leave the solder joint quality as guesswork. If you can, stick with TSSOPs and other parts with visible leads.

3. For Passive Parts, Try to Stick With 0602 or 0402 Sizes

With resistors and capacitors, bigger isn’t necessarily better. 0603 and 0402 sizes tend to be at the sweet spot in cost, and all manufacturers can use these size parts. Another reason to use these sizes is availability. In 2018, extreme industry-wide parts shortages led many passive component manufacturers to focus their fab capacity on the smaller parts. In the future, 0603 and 0402 will have the most reliable supply.

4. Purchase Your Parts in Reel

Digi-Key, Mouser, and most other components vendors will sell you a strip of ten 0402 resistors, and many assembly houses can build from those small strips now. That’s great if you just need eight prototypes, but if you need dozens or hundreds of boards built, get your parts on reels. It takes less time to work with reels or long continuous strips, and the pick-and-place machines are happiest with reels in feeders (Figure 1).

Figure 1: Components on reels loaded into feeders.

5. Stick With Surface Mount

These days, through-hole components tend to be hand soldered. That costs significantly more than machine assembly, so use surface mount wherever possible. Surface-mount components tend to be less expensive than through-hole, too. If you do need a few through-hole parts, this is an opportunity to put in a little sweat equity by soldering the through-hole yourself and save a bit of money (Figure 2).

Figure 2: Even larger components, like these battery clips, can be found in surface-mount form.

6. Consider PCB Cost vs. Double-sided Assembly

Putting surface-mount parts on both sides of the PCB is a great way to better utilize space. However, if the cost is more of a concern, and you only have a few parts to put on the back side, it may be more cost-effective to move them to the top side. If you have a lot of parts, the additional cost for assembling both sides may be less than the cost for the extra PCB size, but with a small number of parts, that's probably not the case. Quote it both ways and see which is less expensive.

Summary

By following these guidelines, you can increase your chances of getting a decent price and good quality and service.

Duane Benson is marketing manager and CTO at Screaming Circuits.