Posted by Jefriz: Mon Jul 10, 2006 6:25 pm    Post subject: Probability of smashed ball - hill in the ballbond

Hello Tom,

It seems not clear if the product is running a long time. You mean that the ball have an inner depth just like a hill? (a photo will help) BST methodology had no change, which means that your shear tester controls the 3 to 5 um tool height. For FTIR, please check ------/FTIR.htm If your EDS did not show Carbon, skip this suggestion.

General comment:
1) Your parameters still needs DOE
2) SPC on peak temp would later be necessary to stabilize and predict the process.
3) Are you using wire size > 1.0 mil diameter? Your LCL seems a little too high (anyway, I assume it came from SPC study). FYI, LSL for 1 mil diameter based from MIL-STD883F is only 20 grams.
4) Your BST data had a high standard deviation (10) which means large variation and data are skewed right, which means most of the data are near the LCL.

Recommended areas to consider:
1) Maintain ball thickness atleast 0.5x wire diameter.
2) Need to monitor your bonding temperature is stable within your target value. Overheating may result to smashed ball and underheating can cause poor intermetallics and weak bonding.
3) Adjust bondforce only as necessary. The ball could have been smashed so much.
4) You may need to evaluate a new tip angle for your capillary. This is if the hill on the ball is still present.
5) Verify that no blowing air is flowing towards the bonding stage.

These are just few things that might help, considering details are limited. Let me know the response.

Best Regards, Jefriz

Posted by Tom Wang: Mon Jul 17, 2006 12:06 pm    Post subject:

Hello friend:

Thanks a lot for your kindly help. Now question was resolved. issue is the dirty oven at D/A PMC. We cleaned it well, the ball shear pass. But I did not inspect contamination by SEM. Why? yes. I know X-RAY from sample s the one from underside of sample surface.
But how can I inspect contamination composition?

Farel Wang

Posted by Jefriz: Mon Jul 17, 2006 6:14 pm    Post subject: Oven contaminants

Hello Tom,

Thank you for informing us on the rootcause. Sorry if the oven was not mentioned as a suspect because your EDS result you mention was normal (I assume peaks of Aluminum only). Can you check again your EDS results if you found peaks of Carbon and Oxygen. SEM (high magnified view) would unlikely show the contaminants. Common contaminants are Carbon and Oxygen base which the signature can be characterize by FTIR. Several other composition analysis tools can also be used (pls look on FA tools on this website).

You may also look into your die attach epoxy. Outgassing potentially can cause similar issue even you have clean oven.

As prevention, include a periodic cleaning & PM of your oven (also include SPC monitoring). Don't forget the wirebond stage temp SPC.

To other readers,
I invite others who have experience on characterizing contaminants to comment or add more suggestion. I believe this subject matter is quite interesting.

Best regards, Jefriz

Back to Page 1 of this archived forum thread...