Tell me if I am wrong. Change solder is not an option if the assembly is
qualified per Mil spec. Change of material, such as solder required
re-qualification at assembly level (consider as major change). Questions:
(1) if the assembly is qualified per Mil, why it is fail so early = 1- 8
years is relatively short time consider the designed life is 15 -20 years.
Any process/MFG location/operator/flux changes? You can dig it out from
initial qual report and take a look at the design history. (2) all the
assembly has its own "travellers" for individual S/N, check any MFG rework
history, any field touch up? (3) if the part is COTS, no string attached.
you can do anything to fix it as you wish based on my understanding. I
believe only samples were tested. Most of others are qual by similarity
based on "families" (few of "good guys" were insist to qual each part.. and
take a lot heat for it...they are the ugly ducklings...).
Good luck.
jk
p.s. there also should be a burn-in T/C prior to shipping as normal Mil
requirement, if you do not see any crack at visual inspection (50X rings a
bell) after burn-in T/C, you can breath easy. If someone eliminate the
burn-in by cycle time reduction, the Answer is: no clue what you shipped
out.
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of Maguire, James F
>Sent: Tuesday, June 25, 2002 7:46 PM
>To: [log in to unmask]
>Subject: Re: [TN] fractured solder joints
>
>
>Have you done any cross sectioning or SEM work on fracture?
>
>
>My guess is that fracturing is due to a small stress built into solder
>joints by operators pushing (very slightly) on some of the joints during
>reflow and the joint can (depending on thermal mass etc.) freeze with a
>certain amount of stress still built in and the solder joint
>creeps (even at
>room temp) over time and ultimately fractures. Roger Wild did some
>excellent work on this problem.
>
>Re you fixes, while another solder alloy (suggest Sn96 or one of Sn/Ag/Cu
>lead free alloys) will help it's still (IMO) a bandaid on a poor process.
>If you can't use a reflow oven, then I suggest one of the solder "dam" tips
>where you set a large wedge shaped tip w/solder and don't touch the device
>at all but essentially transfer the solder from tip to lead(s) by drawing
>the tip down a line of pads. Most solder iron vendors make some form of
>this (I'm familiar with Metcals.)
>
>Good luck
>Jim
>
>-----Original Message-----
>From: Patricia Volkman [mailto:[log in to unmask]]
>Sent: Tuesday, June 25, 2002 2:18 PM
>To: [log in to unmask]
>Subject: [TN] fractured solder joints
>
>
>Fractured Solder Joints
>
>My company has been doing hand assembly/soldering on a driver IC
>board for a
>display that is used on a military airplane. The board uses 8 Holt ICs -
>HI-8010SM-32 - http://www.holtic.com/ProPDFs/8010.C.pdf
>
>The boards we provide have been in use for between 1 year and 8 years, the
>actual time is unknown, but it is likely that they have been in place for a
>long period of time.
>
>The IC is a 44 pin QFP J-lead with 0.050 center spacing on the leads.
>
>Our customer has recently found fractured solder joints associated with
>these ICs (identical to those in photo - IPC-A-610C page 12-85 )
>
>It is assumed that the fractured solder joints occured after leaving our
>facilities, caused by airplace stress cycles or ???
>
>I am looking for any information on why these fractures would occur, the
>boards are spring mounted on the plane, the boards measure about 1.5" x 5".
>
>Most importantly, I am looking for a solution to this problem, I am
>currently looking for a more ductile solder...the solder used in the past
>was Kester SN60PB40. I can also change the assembly process if that is
>determined to be the root cause (all hand soldered)
>
>thanks for any information you can provide.
>
>
>Patti Volkman
>(1-800-823-5588)
>
>
>
>_________________________________________________________________
>Join the world's largest e-mail service with MSN Hotmail.
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