Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


DOUBLE SIDED SMT ASSY

JERRY JOHNSON

#8839

DOUBLE SIDED SMT ASSY | 25 October, 1999

FOR A TYPICAL BOARD WITH SMT PARTS ON TOP SIDE THAT ARE A MIXTURE OF ICS, RES, CAPS, ETC., AND THE BOTTOM SIDE HAS ONLY RES AND CAPS THAT ARE GLUED, I BELIEVE THAT THE NORMAL PROCESS WOULD BE TO GLUE, PLACE, AND CURE THE BOTTOM FIRST, THEN PASTE, PLACE, AND REFLOW THE TOP SIDE SECOND. THEN THE THRU HOLE PARTS WOULD BE INSERTED AND WAVE SOLDERED.

IS THERE ANY PROBLEMS OR CONCERNS BY PROCESSING THE TOP SIDE OF THE BOARD FIRST?

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#8840

Re: DOUBLE SIDED SMT ASSY | 25 October, 1999

Jerry: You don't have to yell, we can see you fine

Are your first side component going to fall off of the board or have their reliability affected during second side processing? If not, go for it!! Lots of people reflow through hole components.

Good luck

Dave F

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Joe Herz

#8841

Re: DOUBLE SIDED SMT ASSY | 27 October, 1999

Jerry,

In our house we generally run a glue bottom last but people do it both ways. Our logic revolves around protecting components from being knocked off the board during handling and processing prior to wave solder (this is most important with small passives 0603s). Be sure that the adhesive you are using can withstand a cure and reflow excursion without becoming brittle. I have seen this happen. Parts can either be bumped off during handling, from friction while riding on the washer flat belt or during wave. Handling, especially if you have 0603 passives on the bottom, can be a little scary if your operators don't use the safest practices.

Call your adhesive supplier and see what they have to say. If they tell you, "Works fine, last a long time", do some kind of evaluation. If they say they are not sure, do an evaluation. If they say "don't do it", find another material or supplier.

The ideal test method would be a shear force test. You may be able to get the adhesive supplier to do this for you for nothing.

Good Luck.

Joe.

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Paul Gerits

#8842

Re: DOUBLE SIDED SMT ASSY | 28 October, 1999

Hi Jerry,

normal proces would be;

1st. reflow side (top) 2nd. curring side (bottom) 3rd. insert 4th. solderwave

Reason for this is that you have a better handling and no overdue stress to components in case you do bottom before top. It is also easier to screenprint the reflow side of the pcb when bottom side is still empty. Of course it is possible to do bottom before top but it only will create extra problems in handling and stress of pcb and components.

Regards,

Paul Gerits Technical consultant Philips EMT.

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