Gidday! ( I saw this recently. What people say 'gidday'?. Is it slang or
remnants from an ancient culture?). 

#1. It is well known by Manko, Licari, Wassink and a from a lot of other
references, that a careful design of solder geometries is necessary if
you want to live troublefree. Now, I have practised this myself. We had
a non-compliant pair of materials that had to be soldered together.
After a few tempcykles the joint cracked. After calculations in NASTRAN
and ANSYS and following redesign of the solder joint, there were no
faults even after 500 tempcykles.

Many components may need such a consideration, as some constructions
have to live in a harsh environment, and have to live for long. A new
problem lies on my desk now. This time it concerns small chip
components, 0505 and up. The solder joints today have different looks,
some are meagre, some are fat, some are porous, some are bright, some
are dull....and you know what kind of variations can occur. 

Now comes my question:  Is there, somewhere, design rules based on all
these decades of soldering, rules that can be used in a CAD library? And
for small chip components? 

The analogy is an electric or mechanical construction: who neglects the
importance of the right C value to get an oscillator to work,  and who
neglects the importance of a welding's geometry to withstand the forces
of hundreds of tons? The micro world is also exposed to similar matters,
as I can see, so micro joints should be designed and made with some more
care, won't they?


#2. This is a subsequential question. If you want a chip solder joint to
last for long, to withstand thousands of power cycles, to be litterally
an evergreen, it's obviously necessary to also have a compatible solder
alloy. The alloy composition must, of course, depend on the mismatching
situation, operation temperature etc. Today, things seem to be done that
were earlier regarded as hazardous. Example: a large processor chip
mounted directly right up and down on a FR-4 board, kind of BGA I
suppose. For automotive use! 

Now to the question: What new wonderful solder alloys have been
evaluated to make this new world easier? I have seen some experimenting
with  Antimon, Bismuth, Copper, Silver, Osmium and the rest of the
periodic system. Is there today a bubblegum-solder? I'm eager to hear.


You need not to answer until august, when I'm back from my vacancy.
During that time I will think of no solder at all.

                             See you / Ingemar / EMW

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