IMST Hybrid IC Design

I had not seen Insulated Metal Substrate Technology (IMST) before, however I had read some long boring convoluted literature, and I do not think the author knew much either. This is the faulty chip that I replaced when repairing the Optonica SM-4100 amplifier, and I was very interested to see how these chips fail, and what they look like from the inside. This module has an aluminium back plate, which looked like it could be opened, hence, after some careful mechanical engineering; I was able to open it to have a look.

After removing the outer case, this is what I saw. The PCB tracks are actually mirror finish and reflect all the light. This circuit is very similar to that shown in the Sanyo datasheet.

I can see straight away how this chip failed. Can you see?

Can you see now?

No? OK, I will give you a clue. One of the terminals has burnt as a fuse wire would burn and is partially missing.

When I was testing the amplifier, this was the side that was showing 0 V at the output pin and I suspected it to have an open Darlington transistor. This is visual proof that it indeed was the case and my deduction was correct.

This is how the transistor should look. There are two wire terminals as you can see.

Here is a close-up of the substrate.

Here is a ceramic capacitor. An advantage of IMST is that you can have many transistors on a single aluminium PCB together with conventional components. This reduces the component count in the final amplifier design and is more reliable.

These tiny spider-like devices are actually transistors.

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