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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Question on BGA Solderability

#7353

Question on BGA Solderability | 24 July, 2001

Folks,

Does anyone have data to support that a minimum clearance left around the perimeter of a BGA on a board design can improve its solderability? In other words, if X distance is left open (free of components) around the BGA, could ball solderability be improved? I'm assuming air flow would be increased to some degree. Let me know what you think.

Thanks in advance for your help.

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Steve Schrader

#7355

Question on BGA Solderability | 24 July, 2001

Greg,

The increased space and hence potentially increased airflow will have no effect on "solderability." It may effect the temperature that the balls see and that is a different issue that can be worked from a profile standpoint if you are not hitting your desired temperatures. The reason you want to leave space around the BGA is to have room for your rework nozzle (should you ever need it) and maybe for inspection (depending on if/how you inspect your BGA's).

Steve

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#7356

Question on BGA Solderability | 24 July, 2001

Steve,

I was aware of the rework requirement but was looking more towards the reflow profile. I wanted to know if there was any significant benefit other than rework itself. I suspected there isn't but I just wanted to be sure.

Bye the way--did you once work for Hughes in Gaithersburg? Let me know and thanks again.

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Steve Schrader

#7358

Question on BGA Solderability | 24 July, 2001

Greg,

Yes, I did my tour of duty. Is your boss back from Bermuda yet? If so, tell her to check her email! Thanks.

BTW, there could be a benefit to moving parts, but that would be dictated by your ability/inability to achieve a proper reflow profile on the board as is. Are you having trouble reaching the temperatures you desire on the ball/pad interface?

Steve

steve@patton.com

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#7364

Question on BGA Solderability | 24 July, 2001

Your theory of reflow heat shadowing has some merit, if your oven is IR. If you oven is primarily convection; no, your theory lacks merit. The primary reason for a keep-out around BGA is to provide for repairing the device without having to depopulate a handful of other components prior to working on the BGA [as an earlier poster posed]. We brickwall BGA on both sides. [A BIG contributor to our ability to assemble these boards is the competent person that laid-out the boards.]

Now in developing Theory B, we might be able to play-off of the general premise of Theory A [heat shadowing] => There is too little heat to make the solder flow properly. Test this theory by profiling on the pad where the solder doesn�t flow well.

As the time after posting this thread increases, we generally propose additional theories. Rather than us speculating, please collapse the discussion by describing the particulars [eg, oven, profile, flux, board, solderability protection, component, breadth and extent, etc.] of the situation.

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