A Cautionary Tale: Solder Will Not Wet SMT Cap - Doh!

[Paul Bryson]

I was completely stymied.  I was hand soldering some 1206 SMT capacitors or I should say I was failing to solder some capacitors.  I tried two different kinds of flux and also solder paste; but, none of the capacitors from this tape will accept solder.  I simply could not get the solder to wet the ends of these caps.   They repel it like Teflon.

I finally looked at the data sheet ... and I noticed it said, "Chip Monolithic Ceramic Capacitor for Automotive limited to Conductive Glue Mounting."  I suppose that is why they won't solder. I had never encountered such a thing before.  I guess I will have to be more careful when ordering "generic" chip capacitors.

 Part no: GCG31CR71E335JA01L (Murata)

[T3sl4co1l]

Well, it's Pd: https://search.murata.co.jp/Ceramy/image/img/A01X/1R0121A.pdf

Should be easy enough to solder, unless maybe it's got some kind of coating on it.  But I don't have a clue what would be strong and
conductive for silver epoxy, but not solderable with rosin.  One article says Pd is harder to tin (maybe need more reactive flux, or more dwell time?), but, it's a noble metal, or reasonably noble, it's not like Ni with the oxide coat, flux shouldn't make a big difference.  Maybe it just needs to be struck with electroless tin first, dunno.

Tim

[Paul Bryson]

I also found this in the data sheet notes for the cap:

"This product is chip monolithic ceramic capacitor limited to conductive glue mounting. Do not apply mounting method
 other than conductive glue. Flow or reflow soldering can result in a lack of adhesive strength on the outer electrode by
 poor wettability, which may result in chips breaking loose from the PCB."

I can truly attest that this is true.  Solder will not stick to these caps.  These caps were listed along side other "ordinary" caps when I did a search on Mouser.  I just assumed that I could solder them.

Lesson learned - these caps exist and will ruin your board if you do not notice that they are not "ordinary".

[rsjsouza]

Indeed an interesting corner case of component selection. Thanks for the heads up.

An article from AVX about this:
https://passive-components.eu/conductive-epoxy-capacitor-mounting-explained-avx-technical-paper/

[Whales]

Wow that part looks absolutely identical to a normal SMD cap.

This reminds me of the time I couldn't get my solder wire to melt. I kept increasing my iron temp to no avail.  It turns out that my wire was actually a straightened paperclip. 

I never knew conductive epoxy assembly was a thing, thanks for the link.  I wonder if epoxy whiskers are a thing?

[tooki]

I can truly attest that this is true.  Solder will not stick to these caps.  These caps were listed along side other "ordinary" caps when I did a search on Mouser.  I just assumed that I could solder them.

In all fairness, Mouser does have the parameter “Termination” set to “conductive epoxy” for these. So they aren’t entirely “standard” (one of the other Termination options). Though I’ll be honest that I probably would not have interpreted that to mean “must be attached using conductive epoxy”, but more likely just as “made with conductive epoxy”.)

[newto]

This reminds me of the time I couldn't get my solder wire to melt. I kept increasing my iron temp to no avail.  It turns out that my wire was actually a straightened paperclip. 

One of my coworkers grabbed some solder off our repair bench to do a minor repair, and just couldn't get his soldering iron hot enough to get it to melt! He came over to complain about "that dang lead free solder, never works right".

Turns out he grabbed our spool of buss wire instead...

[tooki]

I’ve done that too. :p

[KE5FX]

Yeah, my first clue is usually, "What's that awful smell?  Oh, it's my fingers burning."

[T3sl4co1l]

Yeah, my first clue is usually, "What's that awful smell?  Oh, it's my fingers burning."

The joke I heard was in a shop where the old fogies were tinning invar leads, in hand up close and personal, then the newbie tried the same technique with regular copper wire and got a surprise, not knowing the key difference.  (Invar is often supplied copper-plated for easy tinning and good sealing in glass.)

I never knew conductive epoxy assembly was a thing, thanks for the link.  I wonder if epoxy whiskers are a thing?

Nah, unique to tin metallurgy, and a couple others; silver and zinc can also whisker.  The silver flakes that make up silver-loaded epoxy, I think, won't be thick enough to source enough material to whisker more than microscopic distances (which might well effect a reduction in joint resistance, lol).

Tim

[meshtron]

Just wanted to chime in and say thanks for posting this - it's an alligator I didn't even know to watch out for!

[Whales]

\The silver flakes that make up silver-loaded epoxy, I think, won't be thick enough to source enough material to whisker more than microscopic distances (which might well effect a reduction in joint resistance, lol).

"*Datasheet typical resistances are specified after 2 years of leavening"

[vk6zgo]

Wow that part looks absolutely identical to a normal SMD cap.

This reminds me of the time I couldn't get my solder wire to melt. I kept increasing my iron temp to no avail.  It turns out that my wire was actually a straightened paperclip. 

I never knew conductive epoxy assembly was a thing, thanks for the link.  I wonder if epoxy whiskers are a thing?

The old trick, back in the day, was to roll off a few 100mm of your mate's solder roll, cut the solder, insert a length of Tinned Copper wire, soldered at each end to the existing solder (difficult to do, but practical jokes need some effort expended), then roll it all back to look normal.
The TCW performed the same function as your paper clip, but obviously, delayed for maximum hilarity.

[T3sl4co1l]

Hmm, tricky to pull off; even annealed copper is stiffer than even lead-free solder, and when do you find annealed bus wire?

Tim

[vk6zgo]

Hmm, tricky to pull off; even annealed copper is stiffer than even lead-free solder, and when do you find annealed bus wire?

Tim

Back then, the default solder gauge was thicker than commonly used now.
It normally came on the same sized reels as TCW, so the latter already had a similar curved shape coming off the reel.

[Slh]

Another thanks for posting this. I've never come across them but can imagine I'd make that mistake at some point.