1206 pads -- 0805 parts?

If my boards have 1206 pads and the assembler wants to use 0805 parts, do I need to change the PCB art or will the 1206 pads be ok? Anyone run into this? THANKS.

Reply to
mkr5000
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If you design for manufacturing (DFM), use fitting pads.

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Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de 

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt 
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Reply to
Uwe Bonnes

In general no it will not work but it depends on the 1206 footprint you have used. You will have to check. I had this situation for a limited time when the 1206 part designed-in was unavailable and we got by by hand placing a 0805 substitute at an angle but it was not pretty.

piglet

Reply to
Piglet

I have created 1206 and 1210 footprints that include pad extensions for 0805, allowing for assembly flexibility. It does limit the trances running between the pads.

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    - Win
Reply to
Winfield Hill

Isn't the assembler responsible for the result?

Why does he want to make this change? Why does he care what size parts are used??? Seems odd, smaller parts have more problems with tombstoning although I don't know this is an issue with 0805 parts.

I've asked assembly houses to go in the other direction. I've had to make part changes and didn't want to change the art work putting an 0805 on 0603 pads.

Without some justification I wouldn't permit the change. I'm wondering though why you used 1206 parts when they were available in 0805 packages. Usually the engineer is trying to save board space. I guess your design is not tight.

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  Rick C. 

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Reply to
Rick C

You'll get tombstoning in reflow, if you just direct sub in the fab line.

If you're doing just s few, or doing it manually, you can get away with it, by checking each and evry one of them.

RL

Reply to
legg

If he wants 0805 because he has stock and it will save you money and time, if 0805 has sufficient power dissipation, if it's just a very small run, if there are no tracks between 1206 pads, if changing the artwork is a major issue, then I'd probably go for it but make sure the boss approves in writing or audio recording.

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Cheers 
Clive
Reply to
Clive Arthur

Piglet wrote in news:r57tij$hf9$ snipped-for-privacy@dont-email.me:

Take two at half value each and stand up a tee pee for series final value hand soldered applications. For manufacturing, not.

And yes, it still meets IPC-A-610 rev f.

Not suitable for production numbers UNLESS you REALLY trust the soldering skills of that assembler and he or she does them all.

Reply to
DecadentLinuxUserNumeroUno

Winfield Hill wrote in news: snipped-for-privacy@drn.newsguy.com:

Isolation value reduction too (for 1206), but that doesn't matter since one is slappin' an 0805 down anyway. :-)

Reply to
DecadentLinuxUserNumeroUno

Rick C wrote in news: snipped-for-privacy@googlegroups.com:

Stupid question. Hand assembly on SMT requires top soldering skills. That buck stops at the person whom put said solderer in the seat.

Obviously the 1206 part is not available. A tech or engineer might want a change for an electrical reason, but this request is from an assembler, asking if it is OK to put an 0805 part onto a 1206 pad is a valid question for a proto or small number run being hand assembled. Unless dissipation comes into it. That would be why he asked, because he doesn't want a hot spot to occur. It depends also, one would guess, on the pad gap the layout package used had.

See above.

Pretty sure he is talking about hand assembly and hand soldering. If he is talking about programming a picker/placer with an undersized part, it is a no go right out of the stencil wiper.

I got no impression he was talking about a build house. He said "my assembler".

Machine assembled means no way it would fly. The answer is a definite no.

Doubtful, but dissipation may be a factor in this scenario. Likely a factor in the assembler asking about it.

Likely an older design, becasue we could certainly do any board smaller with today's 0402 and 0201 stuff, so more must come into play here than PCB real estate.

Never got the notion that he might not have the part?

Since he referenced still being in layout, he could shrink a shitload of parts. not enough info to say.

Reply to
DecadentLinuxUserNumeroUno

Clive Arthur wrote in news:r589e5$9im$1 @dont-email.me:

Hmmm... there is a business in that form of "signature" methinks.

Reply to
DecadentLinuxUserNumeroUno

well the kind of fit, but When I tried that I got some tombstones about one in 400 parts this is probably worse with taller parts.

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  Jasen.
Reply to
Jasen Betts

Same pad gap dimension according to IPC SM-782. But 782 is deprecated, so if you're following IPC-7351B you may have pin-touching-soldermask errors.

As long as the 0805 reaches, it'll probably work. Tombstoning is rare on such large parts.

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
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Reply to
Tim Williams

"Tim Williams" wrote in news:r5dc2o$t50$ snipped-for-privacy@dont-email.me:

Strange since the term came from a time when the SMT parts were even larger than 1206, and 0805, and certainly was viable through that period as well. The thing is that when they are that large, the gap is large enough for a dab of adhesive, so no tombstoning.

It definitely happens in a small contract shop where they might choose to continue using some old paste after it has expired to save cash. Seeing how many parts pop in reflow usually teaches them the reality of their attempt to save money.

Reply to
DecadentLinuxUserNumeroUno

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