msg wrote:

john wrote:

snip

On older circuit boards when ic's were first introduced it was not
recommended to use high pressure air on the boards. One of the main
failure points on early chips was the bonding of the leads to the
chip. This has since been solved but I still remember having boards
fail after they were blown off with high pressure air.


Interesting. What package types were susceptible to this (or did it
matter)? Metal can TO-x ICs seemed to be the most reliable (RTL, HLL,
some DTL, etc.) but I found a lot of early ceramic packages suffered
from bad seals and permitted fungi to enter and grow inside (this
in equipment that had never been wet, just from operating
environmental conditions). These parts seemed also to lack proper
passivation internally.

Regards,

Michael


The ceramic Ic's were supposed to be more reliable but in fact as you
said they had a higher failure rate. The sealant that they used was not
too good since in many instances the tops would come off the IC . I bet
the sealant was probably a little corrosive too.

The first generation of IC's had a very high failure rate in compared
to todays products. They were very heat sensitive and would act up
above 100 degrees F even though the rating was higher. If I found one
bad ic I would just change out every IC on the whole board that had the
same date code and install a second generation ic with the same number.
On some equipment you would automaticly change out a couple of parts
and it was fixed. One company insisted on using the cheapest parts
available but their advertising sold a lot of equipment in spite of the
poor reliablity of the product. Today ic's and transistors , other than
high power transistors, almost never fail unless something external
blows them out. The industry has come a long way since the fifties when
I first started in electronics.



John