DPRG mailing list archives: DPRG: Blasted 2N2222 transistor...

Sun Nov 22 16:17:53 CST 1998

>From: RArrick <rarrick at ix.netcom.com>

>I've never noticed that.  Are you sure it's that way all the time?
>How about darlingtons?  Seems to me that EBC would make more sense.
>Isn't the base in the middle physically?

The bottom (substrate) for NPNs is the collector.  Connection to the
collector is by the mounting of the transistor die.  That's why the
collector connects to the case of the metal 2n2222's (and power transistors)

The emitter and base are typically aluminum and sit on top of the transistor
die.   Base and emitter connections are via wire bonds that are welded
(ultrasonically) to the die (aluminum connections) and then over to the
transistors leads.  The connection can be in any order, depending on how the
manufacturer wants to do it.

To see for yourself, carefully remove the top of a metal 2n2222 using a pair
of diagonal cutters, Dremel or belt sander. (wear eye protection and hold
the transistor with pliers)  blow out the dust and look inside with a
magnifier.  You will see a tiny flat square sitting near the middle of the
can. That's the transistor.  If you were careful and didn't knock the bond
wires off, you'll see them too.

If your subject transistor still has the wires connected, connect your VOM
(set on ohms X1) to the emitter and collector leads.  Bring the transistor
close to a bright light. You should see current begin to flow as light
increases!

Have Fun

Barry Ward
http://www.idea-vision.com

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