Hi richard,
No, this is not an 'Unicum' process, but it is how BGAs were developed. When
larger LLCCCs [for those of you too young--leadless ceramic chip carriers]
could not be used because of premature
SJ failures, we removed the sidewall metallisations at the castellations
[thus eliminating the solder fillets] which allowed the LLCCCs to swim up. When
this proved to be insufficient for SJ reliability, we used solder balls and cast
tin columns [the first BGAs and components with solder (tin) columns--Bell
Labs has a couple of patents on this].
You put the solder balls onto the component by a reflow process [same as a
BGA--it is the high-temperature hand soldering that is the problem with these
components] and you unsolder the components by touching the PCB pad and the
high-melt solder ball, not the component.



Werner

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