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Our team (three hobbyists now developing our first serious device) is interested in soldering/assembling approximately 200 PCBs. We've already found a low-cost manufacturer for the raw boards, so just the assembly remains.

We'd like to keep the total assembly time and cost reasonably low of course, and therefore are considering various approaches.

The numbers are as follows:

  • 200 single-sided PCBs
  • 5 cm X 5 cm board size
  • 30 capacitors and resistors (0603 size)
  • 5 components QFN / QFP
  • 4 components SOIC / SSOP
  • 1 USB connector
  • 1 SD-card-socket

The raw boards may come bunched/panelized as manufactured but essentially, we want to get, on average, each individual board done in less than 20 minutes ideally.

Which one of the following options would you suggest as best? (given the cost constraint and the desired time per board I stated above):

  • Option A: Hand-place components with tweezers, solder resistors and caps with iron, and solder QFN's with hot-air gun ?
  • Option B: Apply solder paste (possibly using a stencil), hand-place components with tweezers, then use a toaster/reflow oven ?
  • Option C: Get it done entirely by an assembly shop ?

Note: All three of us in the team have roughly around 6 months of consistent experience with the traditional soldering method (tweezer, soldering iron, and hot-air-gun). We don't mind any necessary hand-work at all because we're definitely excited about our board, but it would be good to know we're choosing an efficient approach.

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  • \$\begingroup\$ I would suggest B. We do this in-house, and it's a lot faster and better than A. C can be expensive. \$\endgroup\$
    – Rocketmagnet
    Commented Sep 28, 2012 at 13:22
  • \$\begingroup\$ @Rocketmagnet: By better, do you mean more accurate too? I've only done hand-placement till now, but in Option B, does QFN and SOIC placement have to be very precise at the pre-oven scenario? I guess I'm indirectly asking what kinds of durations you log for the placement phase. \$\endgroup\$
    – OrCa
    Commented Sep 28, 2012 at 13:27
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    \$\begingroup\$ Employ teenagers on lose change wages! \$\endgroup\$
    – TFD
    Commented Sep 28, 2012 at 13:29
  • \$\begingroup\$ SOIC is simple. You don't have to be accurate at all. The chip will self align. With QFN, you have to be a little more accurate, depending on the pitch of the package. It's worth investing in an eye lens. \$\endgroup\$
    – Rocketmagnet
    Commented Sep 28, 2012 at 13:55
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    \$\begingroup\$ SSOP gives you slightly better visibility than QFN, and it's easier to fix shorts, even with a slightly blunt soldering iron. \$\endgroup\$
    – Rocketmagnet
    Commented Sep 28, 2012 at 14:19

3 Answers 3

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C: definitely the assembly shop, if you have the wallet for it. That's for you to decide. Ask some quotes, and decide if doing it yourself is worth the effort. Since this is a hobby project you may think your time is free, but then it has to stay fun as well, hasn't it?

edit
Just got this in a mailing from DesignSpark: fundraising may get you started to have it done by a shop. Erik raised 313 218 dollar for a 5 000 dollar target.
(end of edit)

Alternatively, B: Again, get a quote for a stencil. Yet, even applying the solder paste manually will take less time than hand soldering, which I would not recommend: the resistors and capacitors are not much of a problem, but the ICs may take quite some time if you want to do it proper, i.e. all pins soldered and no short-circuits.

Not A: it takes too long and it's messy. I would only do it myself if I could use the oven.

Remember that Jobs and the Woz also hand-assembled their first batch of Apple computers :-)

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  • \$\begingroup\$ The last line "changes everything" ;) Suppose we were to hand-place and toaster-oven them: In your experience, does less than 20 minutes seem like a likely average for the component count I listed, once we get into the loop? I'm especially curious about the placement time, because I don't know how accurate the placing needs to be before the oven. \$\endgroup\$
    – OrCa
    Commented Sep 28, 2012 at 13:21
  • \$\begingroup\$ @Orlando - With the right amount of solder paste the parts will pull themselves to their right position due to the paste's capilarity, so half a mm off for the 0603s shouldn't be a problem. You can save a lot of time working on one panel at a time (or half a panel if the full panel doesn't fit in the oven): place all R1s on the different PCBs, then all R2s, well work as much as possible with the same tape&reel. The oven takes a long preheating, so you 'll have to interrupt the placement to check whether you panel is done. This may lose you some time, but esp. on a panel 20' should be fine. \$\endgroup\$
    – stevenvh
    Commented Sep 28, 2012 at 13:30
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    \$\begingroup\$ But when the first Apple computers were made, the components were large enough to be used as bookends :) \$\endgroup\$
    – Lundin
    Commented Sep 28, 2012 at 13:31
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Options A and B: No, forget it! You will certainly screw up multiple of the QFNs/QFPs ending up spending far too much time trouble-shooting the boards for it to be worth it, even for a hobbyist. Down to 0.5 pitch QFPs are possible to solder by hand if you are good... SD connectors may or may not be possible depending on pitch. QFNs will only cause you trouble.

I have people with many years of soldering experience at my disposal, but each time we want to be cheap and do things like this ourselves, we get problems, ending up with something crappier and more expensive than what we would have gotten from the professionals.

There are always plenty of local, small SMD assembly companies that would be happy to do jobs with this volume for a reasonable price. Don't go ask the big dragons.

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  • \$\begingroup\$ Hmm; what's a reasonable price? We got quotes from a couple of companies that stated around 13 USD each. Obviously, that isn't justified if we can get it done ourselves in less than 20 minutes per board. But on the other hand, we would put greater priority on staying away from the QFN/other inaccuracies that you stated. \$\endgroup\$
    – OrCa
    Commented Sep 28, 2012 at 13:30
  • \$\begingroup\$ @OrlandoCastillo If you are taking option A, we aren't talking minutes, but hours. Option B would perhaps be possible, but then it all depends on how fine-pitched the components are and how experienced you are at doing such solder jobs. Without knowing anything about the US PCB assembly market, 13 USD sounds a bit steep to me. But since most of the cost is the machine setup: if your BOM contains lots of different values, then the price might be justified. \$\endgroup\$
    – Lundin
    Commented Sep 28, 2012 at 13:46
  • \$\begingroup\$ Down voted because shopping recommendations are off topic.. \$\endgroup\$
    – Passerby
    Commented Oct 13, 2015 at 15:52
  • \$\begingroup\$ @Passerby Aha, solder recommendations are shopping recommendations. I see, that makes sense. Now pardon me while I go shop some components with my shopping iron. \$\endgroup\$
    – Lundin
    Commented Oct 14, 2015 at 6:22
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200 PCBs is getting on the high-side for Options A and B. If you have a lot of time on your hands and have some decent tools you can do it with a modified Option B.

First off, you definitely need a stencil. Rather than going to an expensive shop to get a laser cut stencil, try this method using a soda can, a laser printer, and some basic chemicals to do it at home. It's not a huge undertaking and will save you tons of time.

Secondly, forget tweezers. I've been using tweezers for a long time and it can be handy for small jobs but becomes very time consuming when populating a lot of components. Furthermore, I've found it to be tolerable for a few resistors but when you get into larger components, i.e. larger than the jaws of your tweezers, it becomes really difficult to place things without smudging your solder paste all around.

Suction tools can be useful but do not use anything where you control the vacuum with your hand. You're carefully placing components with your hand, there's no sense adding one more job to throw off your precision. I have a SteadyHands device and it works really well both for large components and for small components. It EASILY cuts my assembly time in a third but more importantly it saves me from tearing my hair out!

For reflowing, I've found a toaster oven works just fine. After a few tries you'll know just how much heat to use and when to shut it off. I use a thermocouple routed into the oven but at this point I'm sure I'll be just as good to do without it because I can see when the solder melts and wicks up onto the components. I have friends who use skillets and have had reasonable success but I have not tried it.

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