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Jun 5th, 2013
 
Invensas Bond Via Array (BVA) PoP : A closer look
 
At the recent ICEP in Japan, Rich Crisp, CTO of Invensas, gave a presentation on their Bond Via Array package-on-package technology. i-Micronews thought it was worth… A Closer Look.
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Today's package-on-package (PoP) structures are mainstream technology. Package to package interconnect is generally accomplished by Solder Ball or Through Mold Via (TMV) connections as shown below. Invensas technology creates copper studs using WB tools  and solders these to connections on opposing pads. They call this technology “Bond Via Array” or BVA.


PoP Connections: (A) with solder balls; (B) with through mold vias (TMV); (C) with “Bond Via Array” (BVA)

The WB interconnects are created on a K&S ICONN Bonder. The wire-bond height, position and bond quality depend on:

Controlling factors in stud formation

WB studs on 0.5 mm pitch before over molding

The wires are coated with Palladium (Pd) to act as barrier against intermetallic growth. As long as the Pd coating is undamaged the bonding process can reportedly survive 230 hrs at 175 ˚C. The copper wire studs are then over molded by film lamination. 

Overmolding of BVA: (A) Cross section; (B) Copper studs protruding from molding compound; (C) Close up of protruding copper studs.

The protruding copper studs are mated to solder balls on the second chip package as shown in  the figure below. 

Cross Section of BVA Bond

The warpage for both the packages at the reflow temperature was low enough to allow for package stacking with an IO pitch of 0.24 mm.
Test structures have successfully survived the following reliability studies.

Reliability of BVA test structures

 

 
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