Jim,
If all you are interested in is finding out if
Jim,
If all you are interested in is finding out if ceramic caps are cracked
then the simplest and easiest way I know of is to put the board
non-biased in 85C/85%RH for 24 hours and when you take it out of the
chamber take test probes connected to a 48V non-current limited power
supply and put the test probes across the capacitor. If it blows up it
was cracked. However, you're likely to destroy your board. As John
indicated you have an interesting problem with not many solutions.
If all you want to find out are capacitors were cracked because you had
an issue with hand soldering of other components near ceramic capacitors
that might have cracked the capacitors I think you really only have two
options;
1. Assume as long as the capacitors weren't touched with a soldering
iron that they are okay.
2. Remove (carefully) the capacitors you are concerned about and replace
(carefully) with new ones and cross section the ones you removed and
look for cracks. Carefully means to do the removal/replacement with hot
air or with two soldering irons that only contact the PCB pads and not
the capacitors. That way you'll at lest find out if they were cracked
originally. However if you use the same operator that originally did
the hand soldering for the removal/replacement then all bets are off.
Regards,
George
George M. Wenger
Andrew Wireless Solutions
Senior Principal FMA / Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 [Office] (732) 309-8964 [Cell]
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Maxwell
Sent: Monday, March 09, 2009 8:27 PM
To: [log in to unmask]
Subject: Re: [TN] Detection of potential cracked capacitors and
resistors
Jim,
Chip resistors seldom fail cracked due to a simple structure and
materials
that have high modulus of elasticity. Ceramic capacitor are complex
multi
layer structures with a much lower modulus. Most ceramic caps are
X5R/X7R
and are made with barium which is an excellent x-ray absorber. Plus
x-ray
usually does not adequate to observe cracks. All one will observe are
nick
dark rectangles in the images.
Acoustic microscopy could be used but depending on the chip size and
location of tall parts it may not be practical as the assembly must be
submerged in water while under test. The transducer needs to be
physically
close to the assembly surface precluding most fully populated assemblies
from being scanned. Additionally most assembly cracks are located
beneath
the terminations that obscure definitive imaging while mounted on the
assembly.
Interesting problems with not many solutions.
Regards,
John Maxwell
----- Original Message -----
From: "Jim West" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, March 09, 2009 4:28 PM
Subject: [TN] Detection of potential cracked capacitors and resistors
Looking for a quick/easy way (if this is even possible), to verify if
ceramic capacitors and/or resistors placed on a PCA are cracked.
Can an X-ray be used to check for cracked capacitors and resistors?
We had an issue with hand soldering of other components that compromised
the PCA and could possibly lead to cracked components. If X-ray cannot
detect the cracks, are they other methods of inspecting for cracked
components that you guys can think of? Besides electrical test (PCA's
will
not fit in electrical test fixture now due to hand mounted components).
Thanks,
Jim
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