Charles,
It is my understanding that almost all LCCs are hot solder dipped prior to
board mounting.  Most LCCs are used in high rel. applications where gold
contamination in the solder joint is known to cause solder joint
embrittlement.  LCCs which we solder dip at our company have roughly 2000
microinches of solder thickness on the terminations after dipping.  Did I
understand that your parts have .002 inch thick gold bumps or just a normal
LCC tungsten-nickel-gold termination.  We process a lot of LCCs yet we see
very few components without castellations.  We have an old sample of a .025
inch pitch LCC without castellation but I have not seen any production units
like this in many years.  It is my understanding that the castellation and
the fillet formed are important to a good reliable joint.  If your
application requires high reliability I would suggest looking into solder
columns, high lead balls, or clip-on leads, as possible solutions.  If high
reliability is not a significant issue then perhaps just hot solder dipping
the component prior to board mounting may help.  The fact that there is no
castellation may be contributing to your problem because with a castellation
the excess solder under the package would have a place to go.  Also the
weight of the package in comparison to the number and size of the leads may
be a factor together with the .025 inch pitch.  Most of the LCCs are .050
inch pitch.  I think the big question is did the person who designed this
package think about how it might be attached.  Perhaps they only planned on
using a socket.  Feel free to contact me directly if you wish.
Russ Winslow
Six Sigma
San Jose, CA
[log in to unmask]

-----Original Message-----
From: Charles Barker <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Thursday, August 20, 1998 6:14 PM
Subject: [TN] Help needed: Attaching leadless ceramic smd


>Hi there fellow Techies!
>     I need some advice/suggstions please. We need to attach a custom
>leadless ceramic device to a board. The device is about .5" square with
>rounded off corners and has .025" pitch gold solder to pads on the bottom
>side only. The attachment surface does not run up the side of the device in
>the fashion of a normal castellation found on regular leadless ceramic
>packages.  These pads are .016 x .042 by about .002" thick.
>     The boards are hasl finished. The pads on the board are .016" x .053".
>The first attempt at soldering these was made using a .006" thick stencil.
>That produced all leads shorted together. The next run was with a .004"
>thick setncil. We still experienced some bridging.
>     Have any of you worked with such a device and/or do you have any
>suggestions on the most reliable way to solder such a critter to a board?
>
>Thanks in advance!
>
>Charlie Barker
>[log in to unmask]
>281-552-3328

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