Thursday, July 23, 2009

What Does Jesse DO?

People ask me what do you do? It's often a hard question because there is so much to this industry, that when I say, well I work in high tech, it doesn't quite capture it. It's really more like, I try to figure out whether/why a high tech thing is breaking, broken, or otherwise messed up in various ways. There is a number of techniques that can be used. At my lab we can use optical microscopy, x-ray transmission microscopy, and acoustic microscopy to look at something without messing with it. However, to get a more complete picture of what's going on, you have to mess with it. This is done by removing parts to directly inspect what is left with things like an optical microscope, or a scanning electron microscope (which will be coming soon). Basically I'm making pretty pictures, so I thought I'd show some of them to illustrate what it is that I do.

These are all optical images:

This is a typical BGA (Ball Grid Array) package. From the top down you have the copper heat sink, followed mold compound (plasticy stuff) with filler particles (SiO2 particles), and that's followed by the brains of the operation- the leads connecting to the silicon die. The bottom of the die is attached to the ground though the "die attach" which also dissipates heat.

Here is a closer view of the leads, silicon die, die attach, and the via (metal filled with plastic) that grounds the die. However, in this image you can see that there is a "void" in the plastic filling the via.

This is what's called a "dark field" image. Basically instead of looking at the direct reflections of the light, which makes all of the metal bits very bright, this looks at the sides of the beam rather than the center of the beam. Here you can really see that void.
This is the higher magnifications of the leads connecting to the active side of the silicon die. If you look close you can see the transistors and the pad that the lead frame.

Here you can see the individual transistors (or whatever it may be) which here which look to be about 5um thick. There is an empty pad, or something, off to the far left. You can see the boxed in area on the right is something like 20 um2, and is the pad has now become an intermetalic mixture or alloy.

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