Dave,

As I recall AlN (4-4.5 ppm) has a lower TCE than either Alumina (7 ppm) or
Beo (7.2-8ppm) at soldering temperatures.    One would expect that as the
PWB contracted during cooling (having a still greater TCE), that the
resistor would be in compression - not a problem here!  Is the contraction
of the individual solder joints sufficient to crack the body??

I looked in my records but wouldn't you know it, I am missing tensile
strength info for AlN.  But, yes it is weaker than Alumina.
Al2O3 - 0.193 GPa, BeO - 0.062-0.069GPa, AlN - ?

Flexural Strength -
Al2O3 - 0.274-0.4 GPa, BeO - 0.110 GPa, AlN - 0.25-0.32 GPa

Got me baffled as well.  Never soldered BeO or AlN chip resistors - sorry.

Guess I need to down another Vernors Ginger Ale!

Steven Creswick - Gentex Corp


-----Original Message-----
From: Dave Hillman [mailto:[log in to unmask]]
Sent: Tuesday, April 16, 2002 10:28 AM
To: [log in to unmask]
Subject: [TN] Cracking Chip Resistors


Hi folks! I have ran into a problem which has me baffled and the extra 20
ounces of Coke I consumed this morning didn't bring about any better
thought clarity so I would like to bounce the problem off the minds of
TechNet. I have been attempting to hand solder a chip resistor (50 x 100)
but have immediate cracking of the resistor across the width of the
component. The resistor is either Aluminum Nitride or BeO (I'm still trying
to find out which material). And yes, we are using proper soldering
technique(s) and the resistor pad geometries are our standard dimensions. I
know that the typical resistor body material is Alumina. Has anyone had
good or bad experiences in hand soldering AlN or BeO resistors? Have I run
into a material flexural strength issue?

Dave Hillman
Rockwell Collins
[log in to unmask]

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