An interesting action shot of membrane transfer

I wish I had read Tucker’s lat post before trying this, but since I just got the steam jig from the machine shop I wanted to try it out. My mistake in the two transfers I attempted was that I applied the steam evenly as opposed to the suggested 45 degree angle, but the results were somewhat interesting all the same.

I have noticed that when steam is applied to the membrane sandwich, it does not immediately press the two membranes together as I might have guessed from the weak pressure differential. Rather, water actually gets under the NPN and noticeably swells it up and away from the substrate, and transfer and adhesion only occurs after this intermediate layer is allowed to evaporate naturally.

I captured a few action shots of the process. In the first, the membrane has been (uniformly) steamed, resulting in significant swelling of the NPN away from the substrate.

 

You can already see that it has cracked under the pressure after about 30 seconds of steam. Have you observed this yet?

After about 10 minutes the intermediate layer of water evaporates from between the membranes and contact is made. The next series of images take place over about 30 seconds left to right top to bottom.

 

 

The cracks and capillaries correspond to the visible cracks in the swollen membrane while water is under there.

 

The membrane did not survive removal of the top chip very well.

 

 

Do you let it sit for a while or treat it at all before separating them?

 

Regardless, this all supports the picture so far of adhesion using an intermediate water layer. Nothing particularly new, I just thought the image sequence was worth noting, since I haven’t yet heard you mention swelling of the membrane prior to adhesion when using steam.

 

My final try used the 45 degree-angled steam application suggested, and everything looked really good while it was still in the jig:

 

 

However, as soon as I loosened the set-screws, the membrane wrinkled horribly. The next image is still in the jig, just with some of the pressure from the screws removed.

 

 

and it looks pretty similar once I actually took it out.

 

So, what are you doing differently to achieve wrinkle-free transfers? Do you use a gasket or o-ring in the jig itself in order to even out the pressure applied by the set screws? Do you let them sit for a long time in the jig after apparent adhesion before removing it? Do you wait until adhesion is visible before you stop steaming, or do you steam for only a few seconds and then wait for adhesion to happen? Let me know your thoughts as to why these wrinkles keep appearing.