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Soldering to AlSiC

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  • Indium Corporation
  • This is my second post on the implications of using aluminum silicon carbide (AlSiC) metal matrix composite materials as the heat spreader, heat sink, or TEC medium for thermal dissipation. Previously, I described how the CTE of an AlSiC substrate could be altered for matching mating surfaces based on the amount of SiC filler used.

    These mating surfaces are assumed to be bonded via a solder bond. That begs the question, “Can AlSiC be soldered directly? Is the aluminum metal filler free and in great enough density to provide for metallic surface bonding?”

    In order to be sure of this answer, I went to another AlSiC materials expert, Tom Sleasman, business manager at Rogers Corporation. Rogers Corporation offers a new, special AlSiC variety with an aluminum skin (AlSic-D3), which I thought would have the best solderability of any of these materials, if that was even possible.

     Unfortunately, Tom’s response was, “We do not recommend soldering directly to the AlSiC for the same reasons as to aluminum. Our process yields a part with an Aluminum rich skin on the outside of the part and in all cases [where the AlSiC is soldered] I am aware of utilizing a nickel plating or copper coating process to provide a solderable surface.”

     

    I cannot speak directly to soldering these new aluminum skin AlSiC materials, however soldering to aluminum is a difficult process, which cannot be accomplished without the appropriate flux. That flux is typically acid-based and offered only as a stand-alone product, not as a solder paste or preform flux coating. 

    Based on Tom’s remarks, I conclude that the best way to solder AlSiC is to have it pre-coated with an oxide-resistant metal, such as nickel or copper. Regular AlSiC substrates cannot be soldered without this surface treatment.