Thanks for the info, Scott. That's what I thought I'd seen before...
Leland
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Post, Scott E
Sent: Wednesday, October 28, 2009 10:24 AM
To: [log in to unmask]
Subject: Re: [TN] Birth of a Solderball
I happen to have a test board on my desk with mid-chip solderballs on 2512 sized resistors. The balls are clinging to the sides of the chips and encased in flux residue. I removed a couple and checked under a microscope and the bottom of the balls that were in contact with the board are flattened, but not both sides. The boards also have large balls of solder from the IPC-TM-650 2.4.43 solder ball test. These are paste deposits that were printed and reflowed on soldermask and were still clinging to the board because they were encased in flux residue. They also have flat bottoms. This is SAC305.
Scott Post
P.O.U. 0000-001E-0CTC
2151 E. Lincoln Road
Kokomo, Indiana 46904-9005
765-451-2983 (Phone)
765-451-0287 (FAX)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Wednesday, October 28, 2009 10:03 AM
To: [log in to unmask]
Subject: Re: [TN] Birth of a Solderball
Bob,
Wouldn't mid-chip solder balls in SMT display slightly flat bottoms as well?
Leland
-----Original Message-----
From: Bob Willis [mailto:[log in to unmask]]
Sent: Wednesday, October 28, 2009 8:54 AM
To: 'TechNet E-Mail Forum'; Leland Woodall
Subject: RE: [TN] Birth of a Solderball
You can only really tell from the shape.
Trying to microsection balls is fun, you get a great section then the ball comes out during polishing. I use these images as how not to do sections in my microsection class at college. Next time I am doing some sections I have a board with some nice balls from selective that I have vacuum coated.
In selective and wave if the solder ball is still in a liquid state during contact with the mask it can have a flat bottom. This is normal in air but not nitrogen
Bob Willis
2 Fourth Ave, Chelmsford, Essex, CM1 4HA England
Tel: (44) 1245 351502
Fax: (44) 1245 496123
Mobile: 07860 775858
www.ASKbobwillis.com
www.SolderingStandards.com
New Package on Package Workshops 24th November www.ASKbobwillis.com/PoPWorkshops.pdf
PCB Inspection & Quality Control Workshop 3rd November www.ASKbobwillis.com/faworkshops.pdf
Book Bob's "Step by Step Failure Analysis Workshop"4th November www.ASKbobwillis.com/faworkshops.pdf
Package on Package Assembly & Inspection Workshops 21th January ITRI www.ASKbobwillis.com/PoPWorkshops.pdf
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: 28 October 2009 11:54
To: [log in to unmask]
Subject: [TN] Birth of a Solderball
TechNetters,
Is there any possible way to determine the origin of a solder ball?
We've had a failure because of one, and we're trying to determine whether it came from our SMT or wave soldering process.
We use SAC305 at both, so using the SEM to determine alloy composition is not really helping.
The ball itself is spherical with no "tails" and quite shiny in appearance.
If we cross section the ball, will we see a difference in grain structure due to the differences in cool down rates? Is there anything else we can use or do?
Thanks in advance for your help!
Leland
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