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MLCC soldering and dielectric cracking damage

Hi:

I frequently assemble PCBs by hand soldering MLCCs of the 0603, 0805,

1206, and a few larger ones (and other parts too--as those capacitor-only circuits aren't much fun!).

My hand soldering technique is to use 0.015" wire solder,

  1. first adding a tiny bit of solder to one pad.
  2. Then I flux both pads, and tack the part to the pad with the added solder.
  3. Sometimes at this point, I put my tweezers on top of the part to create a downward force, and reflow the tacked joint to make the part seat squarely on the pads.
  4. Then I solder the other pad-to-part joint.
  5. If necessary to make it look nicer, I add flux and reflow the tacked joint.

The question is this: How much should I worry about thermal stress cracking or otherwise damaging the MLCC dielectrics?

I have heard that using a pre-heated PCB, and soldering the MLCCs both joints at once using hot air is the preferred approach, to avoid damage.

Also, that MLCCs with thinner dielectrics are more susceptible, like high values in small sizes.

Yet in practice, I've never noticed a bad part. Then again, since most of them are bypass caps, it's hard to notice a bad part.

Any experiences with soldering causing MLCC damage?

How about board flexing? What amount of flex causes trouble? Ordinary fondling? Assembling CPU coolers onto PC motherboards is always a treacherous experience! I wonder how many MLCCs survive that experience.

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Reply to
Mr.CRC
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Why not soldering the part onto that pads right away? That how I do it.

I never use extra flux when soldering such SMT parts. The solder I use it 0.015" Kester 8806 No-Clean, leaded.

Tweezers are metal, can scratch and stress the part. I use a toothpick, usually. A fresh one :-)

Suggest to try to practise until they look good without re-fluxing.

IME it becomes a concern for packages larger than 1812. This goes for normal PCB thickness.

I've seen failed parts but (so far) never on boards I hand-assembled.

Fondling? Hey, that can get you in trouble with the laws :-)

That one I don't understand. How can such coolers stress the caps?

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

.

st

nary

lways a

nce.

they are usually attached to the board with some contraption made of springs clips and standoffs that need to snap into holes in the board, it can take scary amount of force and bending of the board to make it happen

-Lasse

Reply to
langwadt

The literature sure says it's not good to hand solder MLCC parts. However, I haven't had any problems with sizes from 0402 to 1812. We use Metcal soldering irons which can be used with lower temp tips than ordinary irons since the tip is induction heated. 0.010" diameter solder is the way to go for 0402 parts. I don't use flux as it isn't necessary for these parts. I have seen problems with cracked caps due to them being too close to the edge of the board (depaneling issues) and bad profiles on an assembly line.

Reply to
qrk

Because if you have only two hands hands, you cant hold the part, solder and the solder iron all at the same time. I have tried. Evolution is not fast enough to grow the third hand.

Heh

Reply to
LM

Learn to read idiot. It is the act of ASSEMBLING CPU coolers onto PC motherboards that this guy does wrong, and you fail to discern. He is obviously striking then physically somehow. Your diagnostic capacity is like nil.

Reply to
StickThatInYourPipeAndSmokeIt

That can tiddly-wink them into neverland. I grab them with the tweezers.

All OK, except that I don't bother with extra flux. If I sometimes wind up with a big ball of solder on one end, I just wick a little of it away.

Not much. Surface mount ceramic caps are, well, made of ceramic. They are tough.

We often put a few bypass caps on the bottom of a board, like around an FPGA when the top is solid traces and there's no room up there. If there are a modest number of them, manufacturing adds them by hand. I've replaced zillions of ceramic caps myself, debugging boards. No problems.

Overkill.

Most ceramic surfmount caps are about 20 mils thick. Some exotics may be different.

If you are too rough removing one, you can rip the end cap. Any reasonable soldering method seems fine.

Not in my experience.

John

Reply to
John Larkin

That is a thermal no no. You should apply the right amount or LESS, never so damned much that you have to remove some.

No shit, dip tracy.

You are an idiot. The ends are terminated to the termination platings precariously at best. Thermal shocks cause detachments, and most of those cannot be detected with simple test instruments.

Is that you method of "debugging boards"? It is a wonder any of your crap ever worked long enough to get sold.

You're an idiot. You being allowed to live way back when you should have been flushed was underkill.

U-be-dumb.

With seems being the key term to take note of. Good job, Johnny. Good job of showing folks your near nil grasp of the subject.

He asked for a quantity, not a yea nay, ya dopey ditz.

Reply to
TheGlimmerMan

ftp://jjlarkin.lmi.net/Cymer_award.jpg

ftp://jjlarkin.lmi.net/NIF3.jpg

Actually, my favorite is a thank-you letter from the Skunk Works. I have it around here somewhere.

Our field failure rates are healthy multiples of Bellcore calculations. Ceramic cap failures are rare.

John

Reply to
John Larkin

None of your production boards are hand soldered, you retarded twit.

This discussion is about the damage which can occur within the terminations of MLCCs when attached manually, which you are 100% clueless about... obviously.

Reply to
TheGlimmerMan

I do a lot of these, on small-volume projects. I have been doing this for probably close to 15 years. I have encountered no more than

3 or 4 cracked capacitors in this time, and I have used up several 10,000 part reels and many smaller reels.

I put a dab of solder on one pad, place the component gently with tweezers while reflowing the already-soldered pad, and then solder the other pad. I don't use flux, other than what is in the flux-cored solder wire.

Yes, the smaller the caps, the more fragile. I don't use anything smaller than 0805 just because they are harder to deal with.

I have straightened warped boards with the parts on them without damage, but that is really asking for trouble. But, I never had any problem with it, either.

Jon

Reply to
Jon Elson

As I noted, some are.

John

Reply to
John Larkin

Black list the idiot John. I only see his crap when people reply to him. ;)

Reply to
Dennis

I usually do, but he said some silly stuff about soldering caps.

John

Reply to
John Larkin

I use a very similar technique (to Jon's) with pointy stainless steel tweezers and I'll do parts down to 0402. Over the last 10 years I have put down between 5000 to 10000 capacitors an have temperature cycled many of the boards. I have never seen a short circuit cap (since I guess about 50% of caps are decoupling I might have missed some open circuits). Recently I've done quite a few bigger ceramic caps like 22uF 16V in 1210 or 1206 packages - these are about 2mm thick but I've seen no problems. I only do prototypes and very small runs (like perhaps 4 boards) like this. The suggestion that you can solder an 0603 part touching only the pad and not the parts sounds like boards with very large pads or theory not yet contaminated by contact with reality.

Michael Kellett

Reply to
MK

The work enviroments I've been in I've always hand soldered SMD parts mainly for prototypes but also some low vol production. Never had a problem (thats not to say that will always be the case!)

Reply to
Dennis

Repair, and debug, also.

What do you expect from AlwaysWrong?

Reply to
krw

When working with some RF prototypes, built on 0.8 mm FR4 boards, we had some failures due to (suspected) flexing causing capacitor end caps to become loose. This might be called ordinary fondling. We even resorted to stiffening these prototypes soldering some thin strips of ordinary board perpendicular to the board along the long side.

Pere

Reply to
o pere o

Interesting. Is that done on "economy class" PCs? I only know the ones that get screwed into place. Similar to this one:

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--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

Absolutely nothing.

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You can't have a sense of humor, if you have no sense.
Reply to
Michael A. Terrell

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