Hi Gary,
Based upon the information that you have disclosed so far on the TechNet
Forum, I would agree with the comment that the pin is structurally OK
but the solder joint is fractured due to the shear force applied by the
attachment of the heat sink. If you are interested in having a stress
analysis of the configuration, and you are willing to provide me with
all of the details relative to the design configuration, which includes
the material combinations used, the physical dimensions, material
properties (specifically modulus of elasticity, and TCE) and etc., I
will take a crack at performing a structural stress analysis that
determines the shear stress level in the solder joints due to the
assembly condition.
Regards,
faz
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon
Sent: Friday, February 02, 2007 8:42 AM
To: [log in to unmask]
Subject: Re: [TN] Mechanical Stress on solder joints
The pin seems to be intact. The solder joint appears to have
caved in and separated from the pin. Something needs to be changed.
Either just tack two pins to hold the Converter prior to have the heat
sink attached, then reflow both pins at the same time and finish
soldering the rest of the pins manually or change the way the heat sink
is attached so that it does not pull the converter during attachment.
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Thursday, February 01, 2007 4:35 PM
To: [log in to unmask]
Subject: Re: [TN] Mechanical Stress on solder joints
Gary-
The bottom line is that electrical solder is not a reasonable load
bearing material. You can relieve the stress in the joints by reflowing
the connections after attaching the heatsink. IF the pins aren't long
enough to make that work, then re-think your mounting, because there is
no way that it will be reliable with the joints under stress, even if
there is no additional environmental stress placed on the system.
Wayne Thayer
>>> [log in to unmask] 2/1/2007 3:51:03 pm >>>
Steve,
This is side view of the module with the broken pin. There is a heatsink
above approximately 0.100 thick with 4 screws pulling the DC/DC
converter upward away from the circuit board. I do not want to place any
solder joints under load wither it be clamping or pulling forces.
Thanks,
Gary Bremer
Senior Manufacturing Engineer, CIT
Phone: 257-4430 extension 2170
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Thursday, February 01, 2007 9:35 AM
To: [log in to unmask]
Subject: Re: [TN] Mechanical Stress on solder joints
Hi Gary!
I have your picture posted. It's at:
http://stevezeva.homestead.com/files/Broken_Pin.jpg
It sure looks like something has pulled or stressed that pin. I'm trying
to visualize the heatsink, but I can't form a mental picture of it, so I
can't say for sure if it was the heatsink or not. But from your
description, it seems pretty probable that the stress that you describe
damaged that pin.
-Steve Gregory-
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bremer, Gary
Sent: Thursday, February 01, 2007 10:02 AM
To: [log in to unmask]
Subject: [TN] Mechanical Stress on solder joints
Gentlemen,
I have a device that failed in the field, the part is a DC/DC converter
that is first soldered to the circuit board then a massive heatsink is
screwed to the converter pulling the device upward because of an air gap
not covered by a thermal conductive pad. Could this be the cause of
damage to the component pins as shown in the attached photo? The solder
used is Sn63 on the circuit board side and the mass of the board solder
joint appears to be twice that of the component.
Gary Bremer
Senior Manufacturing Engineer, CIT
Curtiss-Wright Controls Inc.
Embedded Computing -Subsystem
28965 Avenue Penn
Santa Clarita, CA 91355-4185
Main: 661.257.4430 extension 2170
Fax: 661.257.4782
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<<Failed Module.bmp>> <<heatsink.jpg>>
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