[sdiy] Soldering copper to aluminum using indium

Chromatest J. Pantsmaker chromatest at azburners.org
Wed Aug 18 00:37:49 CEST 2021

Is it not a situation where heat-sink paste and screws/clamps would work?

On Tue, Aug 17, 2021 at 7:08 AM cheater cheater via Synth-diy <
synth-diy at synth-diy.org> wrote:

> Hi all,
> I am modifying a cooler and I was wondering if anyone had experience
> soldering copper to aluminum using pure indium or indium-silver solder
> In97Ag3.
> I have been able to deposit a good bond of solder to the heatsink in
> question using normal Sn60Pb39Cu1 (the Cu is for not dissolving solder
> tip plating) using AmTech NC-599-v2-TF flux.
> However, 60/40 will only have a thermal conductivity of 50 W/mK as
> opposed to 73 W/mK of the Indium-Silver solder or 83 W/mK of pure
> indium, plus indium and the indium solder melt at 156C and 143C
> respectively as opposed to 183-190C for normal 60/40. This is
> important because the heatsink itself has its fins soldered to the
> base using a solder which I think is at around 200-220C melting point.
> However, I am not aware of the properties of indium when soldering,
> and I am curious if anyone has any experience, or can suggest any good
> fluxes.
> I want to solder copper sheet metal (roughly 40x20x1.5mm) to a part
> copper, part aluminum heatsink base (the border between those two
> happens where I have to put down the sheet metal).
> I am hoping for a sturdy bond that will withstand some pressure and
> which will transfer heat well.
> BTW, I know this will require a lot of power from the soldering iron,
> I have six very powerful soldering irons available, and if need be I
> can use them all at once.
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