Mary -
Unfortunately you didn't mention the type of capacitor or the processes you
are having the cracking problems with. Briefly, I am going to assume you are
talking about surface mount chip caps. If so, they are probably a Z5U
dielectric and the value you are using is probably near the top 1/4 of the
capacitor range for that size.
Moisture is 99% of the time NOT your problem. Moisture penetrates very
little beyond the surface of a ceramic capacitor, so it would be a very
unlikely cause.
In my experience, most capacitor cracking is due to either: (1) a wrong ramp
rate for reflow soldering, (2) or if wave soldering, too large a temperature
delta before immersion in a solder wave, (3) too much pickup or placement
pressure in your Pick and Place Equipment, (4) handling damage, or (5)
someone's rejects that were mistakenly packaged on tape & reel and sent to
you.
The above list is not complete, but they are the more common problems for
surface mount chip caps.
Ed Valentine
Electronics Manufacturing Solutions
8612 Mourning Dove Road, Raleigh, NC 27615
Phone: (919) 270-5145, Fax: (919) 847-9971
Email: [log in to unmask]
Website: http://www.ems-consulting.com
----- Original Message -----
From: "Mary L. Sugden, C.I.D." <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, August 22, 2001 5:22 PM
Subject: [DC] Capacitor Cracking
> To: [log in to unmask] Attn: Designer Council Forum
>
> From: Mary Sugden At: [log in to unmask]
>
> Date: August 20, 2001 Subj: Capacitor Cracking
>
> Hello PCB Lovers,
> One of our colleagues is experiencing a "capacitor cracking"
> problem and needs technical reports, articles or any other
> type of information you may have on the causes and
> preventions. Some possibilities are;
>
> Absorbed moisture? He does not know if the caps
> are maintained in humidity proof packaging.
>
> Absorbed moisture? Boards are washed after first
> soldering then subjected to a second loading &
> soldering.
>
> Handling Abuse? The cracking seems to be limited to
> capacitors in specific areas near the board edges
> and tooling holes.
>
> He does not have an assembly flow map so troubleshooting the
> problem is difficult. Our friend needs all the help he can
> get. Please send whatever you can.
>
> As you can imagine, he does not want to post his company's
> name and have it broadcasted with this problem. He says,
> "Business is slow enough as it is." Please send the info
> to me and I will pass it on to him. He will contact you
> directly and express his deep appreciation.
>
>
> Best Regards, Mary
>
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