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 Posted: Sat Oct 04, 2026 6:36 pm Post subject: Die Crack |
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| Mr EE,
I have read some of your responses and I must say they are very informative. Question: in the context of the dtfs process, can you elaborate how can a die crack occur even if there are no traces of package cracks? regards, ogag |
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Joined: 16 Jun 2026
Posts: 107
Location: Paranaque City, Phils.
| Posted: Mon Oct 06, 2026 11:26 am Post subject: |
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| Hi Ogag,
Thanks for posting here in SFE! We’re glad that you find our responses informative. Anyway, cracking occurs at DTFS when the flexural stress applied on a body exceeds its critical fracture strength. This is true for both the die and the package. Thus, whenever you see a unit with a cracked die but with no visible damage on the package, what this means is that the fracture strength of the die was reached before that of the package. ‘Destructive’ flexural stresses at DTFS are normally caused by debris that act as a fulcrum under the package. The presence of such a fulcrum allows greater flexural displacement (bending) of the package when a blade or punch hits its leads or body, resulting in much larger flexural stresses than if the debris were not there. If these flexural stresses exceed both the fracture strengths of your die and package, then you’ll have both a die crack and a package crack. In your case, however, it seems that the die is much weaker than the package, which was strong enough to withstand the stresses. Below are a few things that possibly contributed to this phenomenon. The molding compound has a high fracture strength, which is a function of the compound formulation itself and temperature (the higher the temp, the lower the strength). We’re talking about DTFS, which is at room temp, so we really expect the molding compound to be strong. This is a good thing, so you don't want to change this. The package involved is thin. The low amount of plastic above and below the die allows the package to ‘flex’ more than the ‘brittle’ and ‘less flexible’ die. The die is large, giving forces a longer ‘arm’ that result in larger flexural stresses on the die (Torque=Force x Distance). The die has silicon damage or imperfections such as backside microcracks, ejector indentations, chip-outs. These act as stress concentrators. The die attach has voids that can also act as stress concentrators. Thanks and keep on posting!!! EE |
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Joined: 20 Jun 2026
Posts: 40
| Posted: Mon Oct 06, 2026 3:44 pm Post subject: |
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| Ogag, EE,
Aside from die size, I think the aspect ratio of the die is also a factor (ratio of die length to die width). FARel Engr |
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