No pictures on Steves site yet, but I have observed that CSPs are harder to
heat than BGAs, I have worked on boards that exhibited beautiful solder
connections on 1.27mm pitch BGAs and insufficient reflow under .5 mm CSPs.
Finally, there are CSPs out there with 90/10 solder bumps.
I had an experience with a bug once, a fruit fly must have landed in the
solder paste just prior to placement of an 1206 chip resistor. The result, a
solder fillet with wing, eye, and two legs protruding . . . they did not
exhibit good wetting.
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Earl Moon
> Sent: Tuesday, February 26, 2002 11:47 PM
> To: [log in to unmask]
> Subject: [TN] REALLY EXCITING STUFF AND A BUG IN MY CAVE
>
>
> Hell, It ain't that exciting but it sure got my attention. I asked Steve,
> again, to post three pics on his outstanding site. The first shows the
> overall view, top down of course, of solder columns at 10x. The
> second has a
> bug in it at 60x. Probably one of those little brown "lady bug" like
> creatures infesting us all (damn they're bad, aren't they?). The
> third is a
> more slanted view showing the "columns" that seem partially formed solder
> joints that didn't take.
>
> The strange thing, to me, is the CSP/DSP parts fell off the board on
> arrival. However, a large ceramic BGA on the same board exhibited perfect
> solder ball squat and joint formation.
>
> My question is how do these columns form into almost perfect structures
> without reflowing around and into the balls? Eutectic means, I'm
> told, going
> from a solid state to a liquid state without going through a
> plastic state.
>
> Again, how did this occur without reflowing and effecting a solder joint?
>
> MoonMan
>
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