Posted by DND: Thu Jul 14, 2005 4:55 pm    Post subject: Back side die rounghness

Anyone know the affect of back side of die roughness ?  One of our customers asked for the measurement. But I don't know what contribute of it, pls help explain. Thanks.

Posted by Bala: Fri Jul 15, 2005 12:05 pm    Post subject: Backside Roughness

Die backside roughness can be measured with surface roughness testers after wafer backgrind operation. Typical Ra values of less than 0.05 microns will have a superfine (polished) finish.

Dies that have a higher surface roughness are prone to die backside chipping or crack during dicing operation (If dressing of blade is improper or dicing parameters are not properly optimized) or during die attach operation during the eject mechanism due to localised stress acting on the die.

The crack might explode anywhere in the subsequent stages of thermomechanical stress in the assembly line or in the worst case explode during IR reflow during board mounting process resulting in catastrophic failure of the unit.

Posted by Donnie: Tue Aug 23, 2005 6:52 pm    Post subject: die roughness measurement

In relation to this discussion, I'm conducting an experiment on wafer stress relief (polishing). I would like to solicit some suggestion on what kind of test that are usually used to measure roughness. Is die strength test necessary? Anybody knows the procedure for this and machine used? What do you call this process?

Posted by FARel Engr: Wed Aug 24, 2005 2:12 pm    Post subject:

Donnie,

When you say die strength, do you mean 'adhesion strength between the die and die attach' or the die fracture strength itself? In general you don't need to measure the actual die strength (I'm not even sure if there's an industry standard for this) after wafer polishing, especially if you don't have baseline data anyway.

Just assemble samples using die from the polished wafer and subject them to rel tests: SHRT, TCT, TST, PCT, etc. You're OK if there'll be no failures. I suggest that you also do die shear testing on some of your samples.

FARel Engr

Posted by Guest: Mon Aug 29, 2005 1:06 pm    Post subject: Re: die roughness measurement

Try stud pull after d/a cure. btw, roughness can be measured using a surface profiler.