Assuming you're loading whole boards with many SMD parts on them and not just the one transistor, then obviously a reflow oven is way faster than using a soldering iron or hot air to do components individually.
If you cannot afford the oven initially, a $20 hotplate works fine unless you have large/heavy parts that need to heat-soak. I semi-regularly do boards with 0805s (nice and big and easy for old hands to place with tweezers), SOIC, LQFP, TSSOP, SOT-23 and up to TO-252/DPAK with a cheap hotplate. The surface tension of the solder when it melts will pull everything into perfect alignment on the pads, and it will look way neater than it did when you placed the parts on the paste 🙂 Most boards you buy online (e.g. HASL) are pre-tinned, there is no tinning step that you need to do between receiving the board and laying down paste ready to load parts.
Doing it with solder wire and an iron is very much the hard way IMHO. At least if you use paste, the paste acts as an adhesive to hold the part down where you placed it. If you're using solder-wire, you need to hold the part down with tweezers while you wet at least the first leg (or two for a large part) with the iron, and you must do every part individually.
If you cannot afford the oven initially, a $20 hotplate works fine unless you have large/heavy parts that need to heat-soak. I semi-regularly do boards with 0805s (nice and big and easy for old hands to place with tweezers), SOIC, LQFP, TSSOP, SOT-23 and up to TO-252/DPAK with a cheap hotplate. The surface tension of the solder when it melts will pull everything into perfect alignment on the pads, and it will look way neater than it did when you placed the parts on the paste 🙂 Most boards you buy online (e.g. HASL) are pre-tinned, there is no tinning step that you need to do between receiving the board and laying down paste ready to load parts.
Doing it with solder wire and an iron is very much the hard way IMHO. At least if you use paste, the paste acts as an adhesive to hold the part down where you placed it. If you're using solder-wire, you need to hold the part down with tweezers while you wet at least the first leg (or two for a large part) with the iron, and you must do every part individually.
Last edited:
The OP is talking about a couple of hundred boards, this is not the sort of assembly process you carry out on the dining room table with a $20 hotplate.
Its basically commercial manufacturing quantities.
Its basically commercial manufacturing quantities.
Fair enough, in which case this is nowhere near soldering-iron territory. Oven, stencils (plural!), cleaning station, hot-air station for reworking tombstoned/rotated parts, test jigs/circuits and probably even more will be required. I hope for the OP's sake that there is no through-hole step that he needs to do by hand! Since this is production, there's a whole pile of extra things to worry about: automated testing, packaging, process documentation, stock management, etc. Worlds away from "how do I stick down one of this transistor".
Agreed with the suggestions to outsource it at a scale of 100s, even if the OP's role is "manage the supply chain and do QA". There is significant value to be provided between a Chinese PCBA service, and providing tested & warranted assemblies with a quality-management paper trail to your customer.
There's probably a bunch of extra regulatory things that us DIYers don't normally need to care about, e.g. it almost certainly must be lead-free, which will constrain your choice of solder and PCB processes. Maybe even insurance, depending on jurisdiction.
Yeah. I agree. That's what I'm doing now, (ie., flux, then pre-tin), and all the ones I've done so far have tested fine. And, just to remind all, I'm retired from a Navy cal-lab, trained in micro-min/SMD soldering. Refresher course biennially, and tested annually.
But I really do appreciate all the tips and advice, and things I may not have considered, in this thread. Depending on how this works out, hopefully I can tell you, in the near future, exactly what it is I'm doing.
There's less than a dozen of those SMD transistors on board. All other parts are through-hole. This is a small, high-end audio product company, that emphasizes 100% designed, and hand assembled, in the USA. Now I've said enough, before I get in trouble with the boss. 😛
I may have given the wrong impression. I mean a couple hundred transistors. Each board has about 10. So 10 boards would be a hundred transistors. And they are only one size, as I showed on the penny. If I moved as slowly as one board per day, (which I don't), that would still be a couple hundred transistors per month. Sorry for that confusion.
Ahh say no more 😉
A well-implemented toaster oven with controller can work really well - I've used this technique with great success. But if you're doing 10 transistors a day hand-soldering SOT-23 would not be onerous.
With due respect, is the Boss looking over your shoulder while you work?
How can he or anybody tell hand soldered from oven soldered transistors?
If anything, because the professionally soldered ones will be better soldered, aligned, etc.
Not mentioning less errors.
And you can very well have only SMT parts soldered professionally, then you add the rest, by hand, clipping leads, etc.
No need to go to China either, get a small local assembler.
By the way, are the PCBs made in China?
If so (which I suspect), then your Boss is "cheating" himself, isn´t he?
Are you using Chinese made components?
Same thing.
"Proudly designed and handmade in USA" sadly is only a Marketing phrase nowadays, if you want to be strict about it.
Will this put you out of work?
Very much doubt so, since by my reckoning you will still be hand soldering 90% of more of total components, let alone extra hand assembly work.
Just curious: how will end customers KNOW it´s being hand built in USA?
Will they show a picture of you hand building it in brochure or video?
Not kidding, it´s a serious question.
As of:
IMPRESSIVE qualifications, to be sure, they will definitely help your quality, not sure they improve your speed ; it will still be a long and laborious job.
Good luck.
It's easy to tell hand-soldered smt parts from reflowed parts. He couldn't get away with doing that,
even if he wanted to do so. The mfr could easily send the boards out if they wanted to do that.
even if he wanted to do so. The mfr could easily send the boards out if they wanted to do that.
Since this is a commercial product, you should be using leadfree solder.
Manufacturers stopped using leaded solder at least 15years ago when Europe put in place strict regulations banning the use of lead in products. The rest of the world followed.
In fact there is absolutely no reason to use leaded solder.
Last edited:
Lead solder is not banned in the USA, except for water pipes. Eutectic solder makes much better pcb joints.
Maybe so, but I would imagine any products manufactured would be using leadfree anyway, its the default manufacturing method.
Leadfree soldering is well advanced.
Absolutely not my experience, I've done dozens and dozens and dozens of boards in a converted toaster oven perfectly satisfactorily using a timer and my eyes to determine when the paste has reflowed. Relying on timing alone is asking for trouble if the oven isn't calibrated, but fortunately melting solder paste is highly visible as its shiny!
For instance:
So long as your components are relatively new and freshly removed from their tape/reel packaging they will work as they are free of tarnish/oxide buildup. I use no-clean QuikChip RoHS solder paste SMD291SNL10 (SAC305 alloy) BTW.
I try to avoid SMD where I can but sometimes its unavoidable.
Some of the larger components are fairly straightforward.
The 0.5mm pitch IC's can be fun. I tend to drag solder them then wick off any excess solder with copper braid.
Some of the larger components are fairly straightforward.
The 0.5mm pitch IC's can be fun. I tend to drag solder them then wick off any excess solder with copper braid.