Ok guys, lets talk ECU's

Electronics has advanced a lot over the past 40-50 years since these original ECUs wrote made. Electronic devices are much smaller now. Remember bag phones? Now you can get one in your watch.

The problem isn’t that the new semiconductors are much smaller than the old ones. They can be smaller due to advances in technology.
Most of the heat generated in the power transistor in an ecu is generated during switching ( turning on and off). Resistance increases to turn off. More resistance means more power dissipation in the transistor. Power dissipation generates heat. The slower it switches, the more heat generated. So if the transistors are faster, they can be smaller and don’t generate as much heat. This is a little oversimplification, but is basically what is going on.

So, if the smaller parts aren’t the problem, what is? I think it is two things, some of which has been touched on before in this and other threads.
1. Bad design - The original ecu’s had the transistor on the outside and big metal heat sink exposed to the air where heat transfer could occur. The air carried away the heat. On the newer ones do not have a good heat transfer design. The transistor is buried inside the ecu. No good way to get the heat out. Some are full of sand or some other filler. The sand will act like a heat sink for awhile. When it warms up to the temperature of the transistor, it is no longer removing heat and the transistor burns up. If you only have your car running a few minutes at a time it might last.

2. Quality control - Cheap crappy parts. Shabby assembly. Bad solder joints. Some of the ones I have seen postmortems of didn’t even have the heat sink on the transistor attached to anything.

As Ray said, hit or miss. Maybe you get a good one, maybe you don’t. I bought an old one from him, but I also keep a spare in the trunk.