Ultrasonic Cleaning Prior to Reliability Stressing

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The preconditioning step (SHRT) done prior to reliability testing of samples can sometimes subject the samples to ionic contaminants. These contaminants can result in leakage and other problems that might cause the reliability assessment activity to fail. The archived forum thread below explores the feasibility of performing ultrasonic cleaning after preconditioning to eliminate ionic contaminants in the samples prior to reliability stressing. Note that ultrasonic cleaning can be mechanically harmful to a device, so its use as a cleaning step must be evaluated very carefully before it is officially used.

Posted by Sook Fong: Fri Jul 15, 2005 2:19 pm Post subject: Ultrasonic Cleaning on BGAs prior to reliability stressing

I'm doing reliability qualification on BGA parts. During preconditioning, some ionic contamination may be introduced to the parts so we perform Ultrasonic cleaning before any reliability stress such as HAST, TC, THB, etc.

1. Does anyone out there have the same practise?

If yes,
2. What is the solution use? Or just DI water?
3. What is the solution temperature?
4. How long is the cleaning duration set?
5. In an interval test point of a humidity-related test (such as THB), do you perform cleaning again?
6. If burn-in board is used, do you clean the boards as well?

Thanks in advance,
SF

Posted by Grant: Fri Jul 15, 2005 9:20 pm Post subject:

We also suffer this problem especially in HAST and PCT.
The contamination will impact the contact of FT.
To some leakage and shortage failures, the ultrasonic cleaning is not a bad choice. But to the open failures. It brings little help.
I want to know what type of failures did you meet?

Posted by Guest: Mon Jul 25, 2005 12:13 pm Post subject:

Hi Grant,

In THB, I see dendrite growth between traces in the substrate. My FA Engr thinks it is due to contamination or condensation as it grows in spots (looks similar to delam spot on a PCB). It gave me leakages & shortage. No opens. I have some pictures if you're interested to see.

I've contacted some experts who advised to clean after precon but not during moisture tests interval. How do you do it?

1. What is the solution use? Or just DI water?
(I found a solution from Alconox)

2. What is the solution temperature?
I think at room temp. The higher the temp, the stronger (reads more damaging) the cleaning is.

3. How long is the cleaning duration set?
I think 5 minutes

Your thought?

Thanks,
SF

Posted by Grant: Thu Jul 28, 2005 10:04 pm Post subject:

Thanks!

We are now doing a experiment on cleaning after precon and before PCT to see the performance.

Hope it will useful and enough to solve this issue!

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