alt.engineering.electrical

msg wrote:

> john wrote:
>
>
>
>> 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