Hi Leo,
Of course, the point of the 90/10 solder balls is to be non-melting/non-collapsing during a eutectic SnPb soldering process, giving you a solder joint height ± the ball diameter ~32 mils vs. the collapsed eutectic ball with a height of ~20 mils. Everything else being equal this would improve the reliability by increasing the cycles-to failure to ~250% of the collapsed solder balls.
Werner
-----Original Message-----
From: [log in to unmask]
To: Werner Engelmaier <[log in to unmask]>
Sent: Mon, May 17, 2010 10:17 am
Subject: RE: [TN] MORE 90 / 10 SOLDER BALL QUESTIONS
Werner,
It was not my terminology - it was one of my colleagues.
I was not surprised at the line of demarcation, per your rationale.
Along those same lines, if the thermal profile reached a sufficiently
high temperature for a long time period, would the eutectic SnPb solder
wet over the 90/10 solder ball as per the left hand solder joint?
Evidently the solder joints fail during test. But when the solder balls
were replaced with new 90/10 solder balls and soldered with eutectic
SnPb solder, the assembly works.
Have you ever seen anything like that?
Lee Whiteman, PMP
Senior Member Engineering Staff
L-3 Communications East
Telephone: (856) 338-3508
FAX: (856) 338-2906
E-Mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Monday, May 17, 2010 10:06 AM
To: [log in to unmask]
Subject: Re: [TN] MORE 90 / 10 SOLDER BALL QUESTIONS
Hi Lee,
What do you mean by 'acceptable?'
Since the 90/10 balls are picked so they would not melt in a eutectic
SnPb profile to preserve a large stand-off to give you good reliability,
a demarcation line is to be expected. After all, you are soldering to
another metal, in this case 90Pb/10Sn.
Werner
-----Original Message-----
From: Lee Whiteman <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, May 17, 2010 9:52 am
Subject: [TN] MORE 90 / 10 SOLDER BALL QUESTIONS
I just posted a photograph of a 90 Pb / 10 Sn BGA solder joint on the
IPC Photo Gallery, that was soldered with eutectic SnPb solder and an
eutectic SnPb solder thermal profile.
The BGA on the left hand side is "acceptable", but the BGA on the right
hand side shows a clear line of demarcation. My initial thoughts was to
check the thermal profile, to see if it got to a high enough
temperature.
Any thoughts and comments?
Thanks.
Lee Whiteman, PMP
Senior Member Engineering Staff
L-3 Communications East
Telephone: (856) 338-3508
FAX: (856) 338-2906
E-Mail: [log in to unmask]
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