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Questions relating to designing PCBs
By peskywinnets
#110761
I'm having good success with 1206 SMD parts & SOIC, but space is *very* tight o my PCB, so I now find myself looking at 16 TSSOP (whose pitch 0.65mm - not sure what that is in old money, something like a 1/4 of the diy friendly .1" pitch) & wondering - is this do-able for a modest home setup (have UV box & bubble etch tank) for someone that that has his eye on getting a small time product out in the marketplace.

I'd be hoping to sell 3-5 units per week, so if I do go TSSOP, it has to be repeatable & trouble free - for example, for anyone doing 0.65mm picth, does stencilling work ok with no bridges etc? (I've yet to try my hand at stencilling, but ovbiously it's the way to go for small runs)
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By leon_heller
#110762
I don't have any problems making my own prototype photo-etch PCBs using parts like that. Hand-soldering works fine. I wouldn't make an actual product like that, though; I'd get the boards made and assembled professionally.
By peskywinnets
#110765
And therein lies the rub - I'm reluctant to get a run of boards made up (& populated with parts!) until I know if the product is viable - I'll not know if the product is viable until I make one & get it out in the marketplace.

If it transpires that it sells well (one can hope), then of course I'd have them made, but if you're only wanting under 25 boards made/populated then surely it's better to do it at home?
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By viskr
#110766
I also hand assemble boards, at least prototype runs. For up to 100 boards they will be also hand assembled, but by a professional. Beyond that it makes sense to get an assembly house involved.

0603 is pretty much where hand assembly is reasonable. 0603 also seems to be the sweet spot (min cost) on the cost curve. For ICs, 0.50mm spacing is still fairly easy to do by hand. Note when I say by hand, that's using a microscope and a good iron (I prefer Wellers, but also have a Metcal).

0402 parts are so small that assembling by hand is tricky and the amount of heat you end up using can alter the part characteristics when done by hand.
By peskywinnets
#110768
But say 0805 passices & 0.65mm pitch ICs (TSSOP)?

I guess the main threat is solder bridges....(and the thought of a microscope for the few TSSOP 14 & TSSOP16 devices going on each board is not that appealing!) So just wondered if stencilling at such a fine pitch (for the DIYer at least) is viable....towards a faster turnaround time per board?
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By ohararp
#110778
A part that tight will more than likely require vias. I'd go with boards made overseas and use a stencil with a hotplate to assemble everything at your place. There are tons of tutorials out there on this process. I also make/sell stencils, but am also more than happy to contribute to help others get their ideas off the ground.
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By FartingMonkey92
#110831
For teeny-tiny stuff, go with the "Tack one leg down and glob over the rest" technique...

Be sure to have some 1-1.5mm de-soldering braid and decent flux, and get your angles just right so the solder wicks onto both land pad and IC lead.
By tstalcup
#110842
I just put together some prototype boards - they were 4 layer 1.2" round boards, with a 64 pin QFN, and 15 or so 0402 and 0603 passives, along with a few other random components. I got 12 boards for $200 from Sunstone, $25 stencil from Ohararp, and did all of the assembly with a $200 hot air/iron combo unit. It was my first attempt at SMT soldering, too, and it went reasonably well. Some problems with solder bridges on the 64QFN, but 5 minutes with solder braid fixed it right up. I should mention that I did not have a microscope, just a 10x loupe for inspection.

I'd recommend looking at PCBPool - they're cheap and you get a free stencil. Check out their pricing - a quick test of their online calculator gives:

(4) 2" x 2" double layer boards
solder mask both sides
silkscreen top only
Free stencil
8 working day delivery time
$79.90 total, or $19.98 each

You could also look at batchPCB.
By macegr
#110851
Local PCB houses definitely take the profit out of any project you're trying to sell in small numbers, but that's not the point, is it? The response from selling the first few prototypes should give you enough information to decide if you want to invest the money to have a few hundred boards made up. You'll sell the first few at a loss to gain this valuable information. Selling naff home-etched boards will not provide accurate real-world data. I reserve home-etched boards for base level prototypes and one-off projects I'm sure will not be products any time soon.

I've soldered TSSOP without a solder mask exactly twice and did not enjoy the process.
By NleahciM
#110857
viskr wrote:I also hand assemble boards, at least prototype runs. For up to 100 boards they will be also hand assembled, but by a professional. Beyond that it makes sense to get an assembly house involved.

0603 is pretty much where hand assembly is reasonable. 0603 also seems to be the sweet spot (min cost) on the cost curve. For ICs, 0.50mm spacing is still fairly easy to do by hand. Note when I say by hand, that's using a microscope and a good iron (I prefer Wellers, but also have a Metcal).

0402 parts are so small that assembling by hand is tricky and the amount of heat you end up using can alter the part characteristics when done by hand.
Out of curiosity - what Weller and Metcal irons do you have?
User avatar
By viskr
#110860
Weller EC1002 with EC1301 pencil.

Metcal SP200

The Metcals are pretty pricey, but offer instant on. I'm not alone on liking Wellers, as 2 of the assembly people I use to build short runs by hand use them too. One works under a scope, the other still uses a magnifying lamp. She has much better eyes than I do.

For hand assembly, use lots of flux and the finest solder you can get. Sorry EPA, but the tin-lead is still easiest for hand assembly. One roll will probably last you the rest of your life, but you might want 2, one very fine for SMT work and one for through hole. I still have the solid lead soldiers my grand father played with, and people worry about lead paint...

Secret is to use as little solder as possible, when you overdue it get our the wick and dip that in paste flux with the iron.
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By ohararp
#110901
I have access to an lpkf router and although the ability to auto drill precisely is nice, it is still not a replacement for real prototype boards from a pcb house. Plated thru holes is the defining point there. I agree macegr on this point.

Vickr also has good points on lead free. Unless I have an assembly house put boards together I won't use lead free. It really messes up your soldering tips and can make your boards difficult to reflow with solder paste. Use leaded solder when you can for ease of use in prototypes.