Now, Marvin, you make my heart pumping extra violently: adhesive problems! What is more exiting. Could be wrangling with Aussidoc, Steve, jk and the other gurus, maybe.
Now, adhesion takes place in a complex way, as you know. The scientists have wonderful ways to describe adhesion, in a way that you see that adhesion is impossible in practice! There are covalent bindings, mechanical bindings, static forces, weak forces, strong forces and US Forces. I have gone through only a fraction, because adhesion theory is time dependent! True! If you ask a specialist from the 40's (no, not the latitude)he will give you one explanation and if you ask a 22 year old professor at Llongborough, he will give another.
If we make sort of a simplification, a general rule for getting adhesion between a 'glue' and a 'metal' could be as follows:
1. The respective atoms must come close enough, we speak about the nanometer range
2. As little disturbing material as possible i.e. few contaminations
3. As little oxides as possible
4. Reliable, clean and well controlled platings
5. Viscosity that matches the two parts to put together
6. Correct adhesive volume vs. catalyst
7. Well controlled process window (quite natural, but not always fulfilled)
8. And...did you ask your supplier for the correct adhesive...yes, of course you did,
(one of our suppliers have 2,000 products for 'glueing')The supplier can tell you that
certain metals (aluminium is one) may cause a chemical interaction that changes the
catalysation and hinders the curing.
If the glue does not wet, as you say, one or many of the above parameters can fail. Among those often suspected is 'contamination' of some kind. Easiest ways to do something use to clean in TRI or another hydrocarbon that removes 'oils and fat'. More complex ways are molecular or chemical particle bombardment, like plasma cleaning. For removing oxides, you may use hydrogene reduction, powder abrasion etc, and, when nothing helps, using a sandpaper or a Scotch Bright (a fantastic allround method, but nothing for microelectronics). Suddenly, the two parts stick together and you measure GPa in shear test, and should be satisfied, but WHAT did you remove? Now comes the real tricky thing. I have performed ESCA, Auger, FTIR and sorts of surface analysis, got 50 mms of paper and diagrams, and still not understood. The scientist says it could be X..or Y..or Z..or even P..or..hello, where are you going..I have more ideas...step..step...bang!
Luckily, glueing use to work without any problems, a wonderful tool. Among my own, rather limited experience, I admire what happens when you put two preparation glasses together with pressure, and put a drop of light 'cyanide' glue on the edge...the glue is sucked in between the two plates with enormous speed by the capillary forces and is cured the seconds after. The two plates are impossible to remove from each other. Mystery! And not a mystery at all.
Finally, my advice to you is that you find an adesive/chemist specialist in you region, trying yourself without background or experience can play you many tricks. If you tell TechNet where you live, I guess you will get adress and names to nearest one. Now, Marvin, look for a life-buoy, you will be drowned in messages from jk, Carey, Aussidoc, RD Chemicals and many more...
Good Luck
Ingemar Hernefjord
Ericsson Microwave Systems
Subject: [TN] How to detect contamination on metal surface
Dear Techneters,
I would like to ask some information as to
how to detect contamination on metal surface and
how do I determine what type of contamination that is.
The said contamination results to poor adhesion
between the glue and the metal surface.
I do hope you would take time in helping me out with this.
Thank you in advance.
Marvin
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