I did a study for European Space Agency that was finished last year in which
we evaluated the reliability of IBM's CBGAs and CCGAs for space
applications, i.e. packages with "hard" balls and columns. One clear result
was that amount of solder paste printed on the solder lands is very critical
for the fatigue life of solder joints to CBGAs. If too little solder paste
is printed, it will result in a meagre solder fillet between the ball and
the solder land on the PCB (since the ball does not melt). If the diameter
of the solder fillet becomes less than the diameter of the ball it will
decrease the fatigue life dramatically. Meagre solder joints may also be
caused by warpage of the PCB and maybe also by some ceramic packages
(depending on their construction and thickness). So if you go for packages
with hard balls, I would recommend that you look over how you control that
the right paste volume is printed on the solder lands prior to mounting the
components.
Per-Erik Tegehall
IVF, Sweden
-----Ursprungligt meddelande-----
Från: Earl Moon [mailto:[log in to unmask]]
Skickat: den 7 februari 2002 21:41
Till: [log in to unmask]
Ämne: [TN] Ceramic CSP's and BGA's in general
Kind folks of the IPC TechNet and those not so but well informed concering
the subject issue - for me.
I have gone back and re-read all the articles and papers concerning ceramic
packages, but for CCGA's. I am, as some of you in the past, about the great
CTE mismatch between ceramic, silicon, and MLB's without constraining or
tailoring core materials.
My "frinds" at TI and IBM have been the primary players in this game. TI's
approach to solder balls is using eutectic types - I belive though not
certain in every instance. IBM talks to hard balls (90% lead) instead - in
most cases as I again believe.
I like the hard ball approach because no collapse, of course, is effected
during reflow. Therefore, more hot air is allowed to "circulate" under and
between the balls effecting a better solder joint consistently.
I am hopeful, some of you can shed some light with positive experiences with
the aformentiond parts and their solder joint acceptable initially, and long
term reliability. Realizing we have gone down this pass a few times, I hope
there is some "new" information besides the great stuff the two companies in
question provide.
As a lover of CCGA's, past and present, by IBM, I wish these parts could use
this technology. It works first and always.
Beyond this, I am hoping TI, as a major DSP device supplier, proves its
plastic BGA (super BGA or perimeter BGA - whichever) does the job. It is
said they are packaging four chips in this package style making it lower
cost and certainly more reliable due to the CTE issue.
Any input appreciated,
MoonMan
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