3
$\begingroup$

I am trying to make an electrical connection to a silicon wafer using a wire (approx 32AWG).

I find that conventional lead/tin (60/40, no flux) solder cannot adhere well to the silicon wafer, since the solder will simply fall off the wafer after cooling (same to both polished and unpolished side of wafer).

I tried depositing a layer of aluminium (1µm thick, by DC sputtering) on the silicon with the guess that solder and silicon were incompatible. However, the adhesion between the sputtered aluminium layer and the solder was still very weak.

What can I do to the silicon wafer so that I can make an electrical connection to it?

$\endgroup$
4
  • $\begingroup$ en.wikipedia.org/wiki/Wire_bonding $\endgroup$ Sep 20, 2015 at 2:35
  • $\begingroup$ Thanks, I have thought about wire bonding, but the diameter of the gold wire is too small and the gold wire prone to breakage. I would prefer using a much thicker wire. $\endgroup$
    – hobbes33
    Sep 20, 2015 at 3:19
  • $\begingroup$ Put down 100 wire bonds. Seriously... if you can work with silicon you must know how to wirebond. OTHO... maybe the hypothesis that you know how to work with silicon is already falsified by the question? Why in the world would you even try to solder silicon???? $\endgroup$
    – CuriousOne
    Sep 20, 2015 at 4:02
  • $\begingroup$ I have a 10mm×10mm silicon sample to be converted into a water splitting working electrode. The piece of silicon chip will thus have to be immersed in electrolyte, possibly with the electrolyte being constantly stirred so as to maintain homogeneity. I will need something to hold the chip physically, and to make an electrical connection to it. With wire bonds, I still have to figure out how to hold the chip physically, then to make another stronger electrical connection out to a test circuit. $\endgroup$
    – hobbes33
    Sep 21, 2015 at 5:39

2 Answers 2

2
$\begingroup$

You can't reasonably solder to aluminum, since it almost instantly forms an aluminum oxide layer, and alumina is as close to inert as makes no never mind. The flux that removes oxides from materials like copper simply aren't active enough for aluminum.

There is nothing to keep you from depositing a different metal, though. Gold, silver, copper or nickel will all work. And I'd recommend something thicker than 1µm.

As I recall, gold with a nickel plating used to be used - the nickel keeps the gold from migrating into the solder and causing embrittlement.

Wikipedia, of course, has a basic treatment of the subject.

$\endgroup$
1
$\begingroup$

I used indium solder to do this. However, there is a trick to it. Silicon wafers typically have a layer of insulating oxide on them. You have to get the indium through the oxide layer into silicon. Put small blobs of indium on the silicon sample where you want to make the connections, and put the sample on a hot plate. Once indium melts, rub each blob in for several minutes with the tip of a sharp, pointed object like a tungsten carbide scribe. I think this process creates small scratches in the oxide layer and molten indium can diffuse into silicon through them. Note that silicon oxidizes even more quickly on the hot plate, so you don't want to keep it there for too long.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.