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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Tomb Stoning

Jeff Ferry

#10573

Tomb Stoning | 16 July, 1999

We have been asked to rework several thousand bare circuit boards. A design change now requires 2 chip components where 1 was originally required. Round test pads near this area will be used to complete this circuit rework, however these test pads are not the proper size. 1 end of each chip component will share a single test pad, the other ends of these chip components will be soldered to separate pads. Tomb stoning will result during automatic solder reflow unless the pads are trimmed to the proper size. The question is what should the relative size of these 3 pads be to eliminate tomb stoning. 1 pad will share 2 solder terminations, the other 2 pads will each have a single solder termination.

Thanks in advance for your expert advise.

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ken

#10574

Re: Tomb Stoning | 16 July, 1999

Jeff, if you have not already tried this, try a longer, more gradual reflow phase in your profile. This has worked for me to eliminate tombstoning during similar situations where non standard component pads were used. It may provide you a useable alternative until the pads are redesigned.

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George Verboven

#10575

Re: Tomb Stoning | 22 July, 1999

| We have been asked to rework several thousand bare circuit boards. A design change now requires 2 chip components where 1 was originally required. Round test pads near this area will be used to complete this circuit rework, however these test pads are not the proper size. 1 end of each chip component will share a single test pad, the other ends of these chip components will be soldered to separate pads. Tomb stoning will result during automatic solder reflow unless the pads are trimmed to the proper size. The question is what should the relative size of these 3 pads be to eliminate tomb stoning. 1 pad will share 2 solder terminations, the other 2 pads will each have a single solder termination. | | Thanks in advance for your expert advise. | If you have to rework that much it is possible to dispence a small glue dot for those components... the glue will cure during preheat even when You use a Reflow profile.

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