Russell Kent wrote:

Finn Lassen wrote:

I had one of my coils (stock)  mounted on the engine mount plate until Tracy
pointed out that the cooler you mount them the better (electronics fails a lot
faster when ambient temp goes up). Don't know if that's an issue here, but thought
I mention it.

I cannot speak for your specific components, but for electronic (as opposed to
electrical) components in general, it is the thermal *cycles* more than the maximum
operating temperature that kills them.  For example, Texas Instruments commercial grade
(as opposed to military grade) products are tested to 85 degC (although the data sheets
frequently list 50 or 70 degC as the upper spec limit).  The common reliability test
(for new product designs) is called the 85/85; that's 85 degC at 85% relative humidity,
and the devices are tested after 100, 250, 500, and 1000 hours.  No devices in a new
design should fail under these conditions; if any do then we have to re-work the design.

Thermal cycles induce mechanical stress on the subcomponents of the electronics and
assist other phenomena like electro-migration and ion-migration.  This is because the
lead frame (a copper-nickel alloy), the mounting epoxy, the chip (a silicon-boron
alloy), the metalization layers (pure aluminum, aluminum-copper, or pure copper), the
mold compound (a plastic confection), and the bond wires (pure gold) all have different
coefficients of thermal expansion.

Russell Kent
Member, Group Technical Staff
Texas Instruments, Inc.

 
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