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Component size on double-sided PCB

Rob

#28992

Component size on double-sided PCB | 7 June, 2004

I've been approached by my design engineer who would like to know what is the largest component I can place on the secondary side of a double-sided PCB (without adhesive or glue) and not have it fall off when I run the top side. Currently, I can place DPAKs and several tantalum caps no problem.

I would appreciate any response immediately. Thanks, Rob

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Mark

#28993

Component size on double-sided PCB | 7 June, 2004

It matters on how you setup your oven profile. I have placed J-leads on both sides with no problems. Also, have come across some fine pitch but wouldnt suggest this too often. Give some examples that he would like to see placed on the bottom side of the boards.

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RDR

#28997

Component size on double-sided PCB | 7 June, 2004

the only components I have had trouble with so far are PLCC68 and larger, Large Coils (2b and 3b size) Heavy crystals. Some BGAs if they are not PBGAs. There was a discussion on this and a formula was given to determine if a part will hang under the surface tension of the solder. I cannot remember what the thread was however.

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Rob

#29002

Component size on double-sided PCB | 7 June, 2004

UPDATE: Just for fun... I sacrificed a scrapped board to determine what remained and what fell and this is the result. Board dimension was 18"x9" and .9" thick. Components consist of hundreds of passives plus 386 proc (QFP256), TSOPs, SOLs 14/16/20, TO-260 and ElectroCaps. The only thing that fell off was a heavy Pulse Inductor. The rest remained on the board. Oven temp was 145, 160, 175, 190, 205, 215, 230 (C).

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Rob

#29003

Component size on double-sided PCB | 7 June, 2004

Board is .09" thick not .9". Sorry

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#29005

Component size on double-sided PCB | 7 June, 2004

That's thin board.

The test that you ran is the best method for determining the specific answer.

Bob Willis says, "Use pad mating to lead wetting area. Some have found the ratio to be as much as 44 grams/sq in."

Bob Willis and Phil Zarrow have posted papers on the topic on their sites. [You can find links their sites in the SMTnet Archives.]

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