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Wet-able Cavity Pad to Control Underfill Fillet Height at Die Corners

IP.com Disclosure Number: IPCOM000244832D
Publication Date: 2016-Jan-20
Document File: 2 page(s) / 432K

Publishing Venue

The IP.com Prior Art Database

Abstract

Lowering overall underfill fillet height is desired in flip chip packaging in order to reduce shear stress near edge and corner of die. Unfortunately fillet height is directly proportional to the amount of underfill dispensed in a unit. Low fillet system requires a small amount of volume dispense, which can lead to very little or no coverage at die corner due to capillary effect and surface tension of dissimilar surface condition. Exposing corner die as result of low fillet has high risk of not protecting C4 interconnect near corner area and also makes the unit susceptible to Z-direction die chipping. Figure 1 shows the difference between high and low fillet underfill systems and issues associated with each system.

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Title: Wet-able Cavity Pad to Control Underfill Fillet Height at Die Corners

Lowering overall underfill fillet height is desired in flip chip packaging in order to reduce shear stress near edge and corner of die.  Unfortunately fillet height is directly proportional to the amount of underfill dispensed in a unit.  Low fillet system requires a small amount of volume dispense, which can lead to very little or no coverage at die corner due to capillary effect and surface tension of dissimilar surface condition.  Exposing corner die as result of low fillet has high risk of not protecting C4 interconnect near corner area and also makes the unit susceptible to Z-direction die chipping.  Figure 1 shows the difference between high and low fillet underfill systems and issues associated with each system.      

Figure 1.  High fillet vs Low fillet and issues associated with them  

In order to eliminate issues associated with low fillet underfill system especially for exposed interconnects, a cavity with a wet-able pad on the substrate located near the die corner can be incorporated during substrate design.  The wet-able cavity features an opening of solder resist, which is typical material used as a final layer in organic based flip chip substrates.  The opening has a wet-able pad finish and is located near the die corner.  The main purpose of the wet-able cavity is to retain underfill after dispensing.  This enables a low volume capillary underfill dispensing process. ...