Graham,
There are a couple of reasons. One is the difficulty in getting a
solid glue joint on such a tiny component. As you have seen with the
recent postings, contaminating the solder pads with glue is a problem.
Without glue on these components, they tend to be swallowed by the wave.
The second problem is a process problem by the capacitor
manufacture. Sometimes, a capacitive plate will reach to the exterior of
the capacitor. This exposes the plate, and becomes a potential site for
solder to adhere. If solder adheres to a protruding plate between the
terminations, then, in the non-perfect world of a dirty wavesolder, a HIGH
potential exist for a bridge to occur. (This can also occur at SMT, but it
is worse in the wave.)
The finger pointing then becomes immediate. The assembler saying
its the component manufactures fault, and the component manufacture saying
you can't build them that way.
Although, I must admit, I have not seen this problem in 0603's yet.
However, as the component manufacture is pressed to increase capacitance in
smaller packages, the closer the capacitive plates will come to the surface
of the component. (Even the capacitor manufactures can't get away from the
problems of increasing circuit density.)
Hope this helps
Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]
> -----Original Message-----
> From: Graham Collins [SMTP:[log in to unmask]]
> Sent: Tuesday, July 25, 2000 5:26 AM
> To: [log in to unmask]
> Subject: [TN] wave soldering caps?
>
> Hi All
> Today's question concerns capacitors:
> Going through the data sheets on AVX's web site concerning capacitors (X7R
> dielectric in particular), I find a note that 0402, 0504, and 0603 are for
> reflow soldering only. Also, 1808 and up are recommended for reflow
> soldering only. I understand the reasoning behind reflow soldering 1808's
> and larger, but what's with the small ones? A quick check of the Vishay
> site did not turn up the same process note.
>
> The only theory I have at this point is this: if wave soldering 0603s,
> you may end up with a big solder fillet, perhaps too large to allow stress
> relaxing / creep in the solder joint. Good theory, or is there a better
> reason out there?
>
> Thanks and have a good day!
>
> regards
>
> Graham Collins
> Process Engineer, Litton Systems Canada, Atlantic Facility
> (902) 873-2000 ext 6215
>
> ##############################################################
> TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
> ##############################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with
> following text in
> the body:
> To subscribe: SUBSCRIBE TECHNET <your full name>
> To unsubscribe: SIGNOFF TECHNET
> ##############################################################
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> additional
> information.
> If you need assistance - contact Keach Sasamori at [log in to unmask] or
> 847-509-9700 ext.5315
> ##############################################################
##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe: SUBSCRIBE TECHNET <your full name>
To unsubscribe: SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################
|
