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BGA opens / cracks

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BGA opens / cracks | 24 January, 2007


we are facing some troubles with BGA opens in our production. PCB are both side popolated with BGA. BGA is array of 26*26, with some 6*6 center balls. PCB has 2 reflow processes, 4 pcs of BGA on each side. Now we are partly observing opens on the center balls on those BGA which have seen 2nd reflow process. Cross section analysis have shown micro cracks between ball and BGA pad. No crack between ball and PCB pad. Ball itselfs looks good, and also was soldered before on both pads (you see the residuals) . We have measured temp profiles (lead process) which gives temp over liquidus (200�C) temp for both processes. Does anyone have similar expierences or idea for root cause. Assumption could be thermal warpage of the BGA housing, causing crack during cool down phase.


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BGA opens / cracks | 25 January, 2007

Tricky stuff.

I would expect to hit between 210-215 peak temp on Lead process. What sort of profile are you using? I would imagine a good soak zone would be critical- I have never had BGAs on bottomside so cant really advise any further,i will be interested to see how you get on..


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BGA opens / cracks | 30 January, 2007

Thank you for feedback and comment.

We are trying this again, increasement of solder temp to reach 210-215 peak temp. This is also our norml guideline, but in the past the colleagues had observed problem with that PCB, so reduced it.

I let you know the result. Currently we wait for materials.

Rgds Frank

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BGA opens / cracks | 30 January, 2007

these assemblies getting depaneled? ICT? any fixtures or anything? I would check your print and placement equipment and make sure there are no support issues as well. But I believe you mentioned fractures so that would be happening after the reflow process(s).

If you have seen fractures of these joints then you need to worry about cooling and handling. I believe you mentioned that they were reflowed fine?


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BGA opens / cracks | 4 February, 2007

Profile should have a longer cool soak. Verify as was mentioned all pin/fixture support through out the entire process. Print, Place, pre reflow hand load, post reflow, carriers, ICT, Depanel and FCT. Conformal Coated or Potted? Mylars work well for quick verification of the process. Are you measuring your thermals at the ball to the interface of the cracking/fractured joints?If so what is that temp? What are the times above liquidous? And have you verified vendor thermal limits for this package are not being ecceeded? What is the array size? Individual PCB dimensions? Recess Tabs ro Scored? What is the thickness of the PCB? Do you have vias buried in the lands that are not plugged (Open Vias) Are these hard balls or soft balls? (Eutectic versa Non-Eutectic)

Here to Help!

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BGA opens / cracks | 7 February, 2007

...and, bake those parts. A lot of times, moisture will cause problems like you mentioned in the center of the part. (Old components will get this condition often)

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BGA opens / cracks | 20 February, 2007

FRank, are the BGA's in question a no-lead part? This usually results inthe paste flowing to make the electrical contact and not the ball, so I assume they could possibly crack easier than a leaded part. We have been receiveing almost all our BGA's as no-lead parts, as of late. Having to go to a slightly hotter profile.

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BGA opens / cracks | 25 February, 2007

Dear SMT community,

thank you all for your comments and valuable hints. I am newcomer here and impressed about the feedbacks!

We have made a new lot of 25 pcb with total 200pcs of (leaded) BGA, whith slightly higher temperature profiles ~210�C peak for top and bottom side process and have been successful this time.

We will continue to observe next lots, hoping that the results keep good.

Best regards Frank

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BGA opens / cracks | 25 February, 2007

Just make sure you keep the half done assemblies in dry storage or do the second reflow within the time dictated by the BGAs MSD rating level.

Maybe this time you did the second side with a very short wait because you were anxious about the results and later you go back to doing one side one week then doing the second side a week later.

What do the center balls do on your BGA? On most they are either thermal relief or grounding.

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