Ernie,

Assuming that you are referring to Surface Mount parts. Ceramic parts are
extremely fragile.

If you are using parts larger than 1812's on the secondary side, the
cracking is probably thermal as parts larger than this should not be wave
soldered.

Everyday handling of the board such as placement on the bench and washing
boards in an Aqueous Cleaner can also cause cracking problems. In the
cleaner, placement of the board on the wire mesh belt can lead to cracking.

We employ very cautious handling when working on these boards. Even solder
touch up with a soldering iron can cause problems. That's why we touch up
using Hot Air Tools.

I agree, the cracking is random and does not seem to be caused by a single
event. We believe it to be cumulative so, when we improved or handling
procedures and eliminated wave soldering, the problem did go away. We did
not make adjustments to our pick and place operation. Excessive placement
pressure can also cause these parts to crack.

Hope, this helps. I've posted this phenomenon to this forum from a different
angle a few times. Not too many are willing to discuss this topic. Good
Luck. I am available to further discuss this if you need to.

Bill Kasprzak
Moog Inc., Systems Group, Process Engineer


-----Original Message-----
From: Ernie Fung [mailto:[log in to unmask]]
Sent: Saturday, January 17, 2004 2:43 AM
To: [log in to unmask]
Subject: [TN] Breaking of capacitor


Greetings to all. We are currently experiencing cracking of the ceramic
capacitors, on both primary and secondary sides of the PWB. The cracks do
not appear to alter the electrical properties (PWBs pass in circuit
testing), but we are concerned with long term reliability. Thermal
profiling of all processes, and copying same in defect lab, has not
reproduced the defect! The cracking appears randomly, and is spread across
several vendors. Any helpful suggestions out there? Thanx for your time.

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