Posted by Balapmurugan: Thu Dec 14, 2006 12:17 pm    Post subject: Tin oxidation in 100% Matte Tin lead finish - C7025 base

We observe tin oxidation issue in 100% matte tin lead finish devices in packages with C7025 base material. The problem occurs in only in one or two leads of the package and occurs in random.

The problem seem to appear after storage for a while (about three to six months time).

EDX analysis reveals Oxygen & Carbon on the affected lead. However we regularly check Carbon content on plated deposit and ensure that the same is below 100 ppm.

Any suggestions on the possible causes of tin layer getting oxidized. We handle C194 base material also with the same plating chemistry and don't observe any issues in the same.

Posted by Mike_balbuena: Mon Dec 18, 2006 10:04 am    Post subject: tin finish

Check your storage location. Make sure humidity and temp is well controlled. The material science of tin oxidation is that over time it will accelerate and propagate. The storage condition is the main factor of how fast it accelerates.
Please give me the base composition instead of material number since I'm no longer in semicon. I might be able to see metal interaction and the metallurgy science of it.

Thanks,
_________________
Mike B.

Posted by Balapmurugan: Mon Dec 18, 2006 12:10 pm    Post subject:

Hi Mike,

The composition of C7025 is 3% Ni, 0.65% Si, 0.15% Mg and the balance Copper.

The issue occurred mainly from a specific end customer located in China where the products were claimed to be stored in 25 deg.C, 50 - 75% Rh.

The quite puzzling thing was only one or two leads in each package were found to be oxidized and were appearing dark when compared to the rest of the leads.

What is the worst case storage conditions that the manufacturer shall simulate & verify and what are the accelerated aging methods available.

Bala.

Posted by Mike_balbuena: Tue Dec 19, 2006 12:27 am    Post subject: Tin oxidation

Hi-
What is the nickel barrier content of c194? Is this the first occurrence for C7025?

Could you check the current on your plating bath, are you sure you don’t have excessive fluctuation on the current? Since it could have been burning your plating and will accelerate the oxidation overtime. Please check the grain structure of each leads if uniform or not, check uniformity of plating thickness on each leads as well.
If after optimizing and checking all the parameters and it will not worked try to anneal parts right after plating for 1 hour at 150 deg C. I suggest 25 deg C but 40 to 65 RH. You can try to simulate the effects on the storage environment to see each conditions effect. With 1 or few units affected I’m suspecting your plating parameters, what equipment are you using?
_________________
Mike B.

Posted by Balapmurugan: Tue Dec 19, 2006 11:28 am    Post subject:

Mike,

We changed the post plate rinse water from RO water to Hot DI rinse and monitoring the results.

Also the post plate neutralizer temp was increased from 40 deg.c to 50 deg.C for improving rinse effectiveness.

Bala.