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Solder Bridging on BGA

john_wsme

#20352

Solder Bridging on BGA | 13 June, 2002

Dear All,

We have a SRT BGA rework machine and we created several profiles following solder reflow reqirement, but when we installed BGAs, we saw a lot of solder bridging in the conner. Please give us some ideas to eleminate this problem.

Thanks in advance, John

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RDR

#20353

Solder Bridging on BGA | 13 June, 2002

Having just gine through a similar problem myself (with much less equip.) Here are a few things to consider and/or look at

Do you have the proper pad size? It should be the same size as the pad on the BGA.

Is the board warping during your operation?

Where and how are you placing T/Cs.

What type of package are you working with? PBGA, CBGA, CCGA, etc...

Are you applying paste or just attaching with the balls?

My problem ended up being a combination of pad and PCB design along with a bad thermal ramp. Excessive ramp rates will cause the corners to bend "like tater chips" (this is a copyright infringement of a well known subscriber). what was happening to me was one side of the BGA was going into reflow long before the other side due to copper layout. With the oversized pads it would also allow the part to settle abnormally low and would also cause the part to move around during reflow. I had to apply a much longer preheat from the bottom side and reduce the temp on the top side until the package and board reached 170 C across the entire area. I then apllied just enough heat from the top to bring it up to 200 C. This fixed my problem.

P.S. for all of you that responded to my BGA rework thread "MUCH THANKS"

Oh yeah, I almost forgot: Search the archives for more info.

Russ

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john_wsme

#20357

Solder Bridging on BGA | 14 June, 2002

Ross,

Thanks for your advice. I will take a look at FAB warp and check the pad size. If you also have any suggestions on rework BGA profile, please share some information which is a great help for us.

The best regards, John

Need help from everybody!

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john_wsme

#20358

Solder Bridging on BGA | 14 June, 2002

Sorry, Russ

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#20370

Solder Bridging on BGA | 14 June, 2002

Russ makes good points.

Search the archives for: * Links to rework machine profiles. * Discussion on people causing corner shorts on their BGA, when heating them too rapidly, making the corners to curl like potato [potatoe?] chips.

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john_wsme

#20374

Solder Bridging on BGA | 14 June, 2002

Dave and Russ,

Today we modified the profile to ramp up slowly and have longer preheat time. The result is great, 0 out of 5 without bridging. I did review the FAB design and seen the pad is much biger than ball size. So I guess it is the problem.

Thanks for your help, Have a good weekends! John

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