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Jun 25th, 2013
 
New spin-on temporary bonding solution from Dow Corning: a closer look
 
Dow Corning and SÜSS MicroTec recently announced a new temporary bonding solution for 2.5D and 3D IC packaging which reportedly “…greatly increases the throughput of the temporary bonding/debonding process to help lower the total cost of ownership”. iMicronews thought this was worth… A Closer Look.
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At the recent ECTC in Las Vegas Ranjith John of Dow Corning, presented a paper entitled “Low Cost, Room Temperature, Debondable, Spin on Temporary Bonding Solution:  A Key Enabler for 2.5D/3D IC Packaging” .He detailed the development of a bi-layer spin-on temporary bonding solution that “...eliminates the need for specialized equipment for wafer pretreatment to enable bonding or wafer post-treatment for debonding” and reportedly “takes less than 15 minutes [processing time], with room for further improvement ”

In order to be competitive, temporary bonding solutions must deliver a uniformly thick adhesive coat, and be able to withstand the mechanical, thermal and chemical processes of TSV fabrication. In addition, they must allow subsequent debonding of  the active and carrier wafers without damaging the high-value die.

Dow Corning has developed a silicone bilayer spin-on solution comprising WL-3001 bonding release layer ( spun on from 1300 – 2800 A) and WL-40XX , the adhesive layer, which is spun on between 28 and 100 um. The process flow consists of :

1. Spin coat thin release layer (RL) on device wafer and bake at low temperature (130 – 150 C)
2. Spin coat thick adhesive layer on either device or carrier wafer
3. Room temperature bond
4. Cure bonded stack on hot plate
5. Wafer thinning and TSV processing
6. Laminate wafer pair on tape and debond wafer after post processing at room temperature

 

Dow Corning Temporary Bond/Debond Process Flow

Dow Corning reports a total thickness variation of less than 4.1 µm for 68um spin-coated adhesive film on a 300 mm wafer. In addition, wafers showed good thermal stability when exposed to the 300°C temperatures common to the TSV process.

 

 
Wafer Map of 300 mm Wafer with 68um Adhesive Coating

Thermal stability of a temporary bonding material is critical to ensure mechanical stability during the various processing steps involved in the via reveal and backside RDL fabrication steps. Additionally, temporary bonding materials cannot outgas during the post bond processing steps as it could lead to voids or delamination. Thermal analysis of the new Dow Corning release layer and adhesive layer shows weight loss for either layer was  < 0.5 wt% up to  300 C. No voids or delamination were detected. The release and adhesive layers also proved to be highly resistant to a variety of typical processing chemicals.

Wafers with 70 um tall bumps and a 100um adhesive coating were bonded and debonded on a Suss SBS300 bond cluster.

 

 
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