Eutectic bonding is a process of joining two substrates together using an eutectic liquid to form a solder to bond the substrates together. The formation of a liquid layer allows bonding over some imperfections and some surface roughness. Eutectic bonding requires two materials that when alloyed have a lower melting point than the individual materials. Common combinations in the LNF are Si-Au and In-Au.
|Other Names||Eutectic Soldering|
Finetech Flip Chip Bonder
|Warning:||This page has not been released yet.|
Following is a general description of the tools available in LNF for Eutectic Bonding.
The EVG 520IS can easily be used to bond pieces, 4" and 6" wafers. Heating and bonding can happen in a air or under vacuum. Bond alignment for 4" and 6" wafers is done with the EVG 620 Bond Aligner. The default pressure plate is metal. For 4" and 6" inch samples you will want to coordinate with the tool engineer to use the Quartz plate because it is flatter and will provide more uniform force across you sample.
The default setup on the SB-6E Bonder is for 4 inch round substrates. 6 inch round substrates can also be accommodated but a tooling change must coordinate with the tool engineer. Alignment for 4" and 6" round samples is accomplished using the MA-BA-6 Mask-Bond Aligner in Bond Alignment mode. Heating and bonding can happen in a air or under vacuum.
Finetech Flip Chip Bonder
This is a piece part bonder located in the ROBIN lab. The max chip size is is 15mmx15mm. They can be bonded to a substrate that is 40cmx40cm. The tool works at atmosphere but forming gas is available.
Method of operation
Two substrates are prepared. The substrates can be made of the bonding material or have layers of deposited and patterned if desired. Each substrate is then cleaned. The stack, if required, is aligned and brought into contact. They are then heated and force is applied. The stack is then cooled and removed from the tool.
Eutectic bonding is most often used at the end of processes as part of packaging. It can be used to:
- Create a hermetic seal
- Bond two die together
Here we describe what parameters are of importance in this technology (e.g. power, temperature...). May not be relevant to some technologies.
The two metals that form a unique super lattice that is distinctly different from the individual bulk material. These systems have a lower melting temperature than the individual metals. Not all material combinations form eutectic systems. Common eutectic systems used at the LNF are:
|Eutectic Alloy||Eutectic Composition in wt%||Eutectic/Solder Temperature in °C|
The temperature required will depend on the eutectic system used.
Eutectic bonding requires minimal force. Just enough to bring the bonding surfaces into contact. If to much is applied the liquid alloy out is forced out and the bond is weekend or destroyed.
Vacuum or inert atmospheres are required for most Eutectic Bonds. The elevated temperatures oxides the materials and inhibit bond formation.
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