How easy to damage components through flow soldering?

[Peter]

We have just had a delivery (from a pick/place subcontractor) of a few
thousand populated circuits.

Each one has a 22uF 50N Nichicon aluminium electrolytic cap on it, SMT
type.

I immediately noticed that all the caps have their top slightly bowed
outwards.

So I applied a 370degC temperature controlled soldering iron to the
case of a fresh one of these. After a long time, after the cap was
smoking away quite a bit, the top of it did indeed come up. Eventually
it came up a lot more than those on the PCBs... yet, it still measured
22uF-23uF with a capacitance meter.

I am going to visit the contractor on Monday to see if we can work out
what they did with their reflow oven to cause this.

What concerns me is whether I should scrap all the circuits as a
precaution. If I did that, what legal basis would I have for doing
that? It would be hugely expensive, about US$20k.

The rest of the components are some SO-14/16 chips, HP optoisolators,
loads of ceramic caps, 0805 mostly but some bigger, melf (glass)
diodes, plastic power diodes, etc.

 

[Brian]

We have just had a delivery (from a pick/place subcontractor) of a few
thousand populated circuits.

Each one has a 22uF 50N Nichicon aluminium electrolytic cap on it, SMT
type.

I immediately noticed that all the caps have their top slightly bowed
outwards.

So I applied a 370degC temperature controlled soldering iron to the
case of a fresh one of these. After a long time, after the cap was
smoking away quite a bit, the top of it did indeed come up. Eventually
it came up a lot more than those on the PCBs... yet, it still measured
22uF-23uF with a capacitance meter.

I am going to visit the contractor on Monday to see if we can work out
what they did with their reflow oven to cause this.

What concerns me is whether I should scrap all the circuits as a
precaution. If I did that, what legal basis would I have for doing
that? It would be hugely expensive, about US$20k.

The rest of the components are some SO-14/16 chips, HP optoisolators,
loads of ceramic caps, 0805 mostly but some bigger, melf (glass)
diodes, plastic power diodes, etc.

Reply by email, perhaps I can help.

 

[Peter]

Reply by email, perhaps I can help.

Reposted with my email address.

Peter.

 

[[email protected]]

We have just had a delivery (from a pick/place subcontractor) of a few
thousand populated circuits.

Each one has a 22uF 50N Nichicon aluminium electrolytic cap on it, SMT
type.

I immediately noticed that all the caps have their top slightly bowed
outwards.

Do they work?? The ones I use look like that from the factory!

 

[Brian]

Reposted with my email address.

Peter.

How'd it go at the manufacturer? We do quite a bit of lead free now. I
know many manufacturers attacked it first by throwing lots of heat at
it, NOT the way to go. Yes, I know Rohs is Bull-oni, but if you have
to do it, might as well do it a best you can.

Don't know if this is the problem in your case. hope you solved it.

Brian

 

[Peter]

How'd it go at the manufacturer? We do quite a bit of lead free now. I
know many manufacturers attacked it first by throwing lots of heat at
it, NOT the way to go. Yes, I know Rohs is Bull-oni, but if you have
to do it, might as well do it a best you can.

Don't know if this is the problem in your case. hope you solved it.

I got a bit further now. The contractor had (without authorisation)
reflowed that job using his lead-free oven profile, which is about 35C
hotter. The temp profile is *just within* the published profile for
that Nichicon capacitor (exceed 230C for 30s max, and 250C max) so I
suspect the caps will actually be OK. They measure OK. I am waiting to
hear from Nichicon for a confirmation; I sent them the oven profile.

Their initial informal view was that a bit of gas pressure doesn't
matter, so long as the thing doesn't blow apart...

OTOH we do all remember that business from a couple of years ago when
PC motherboard capacitors were "inflating" themselves all over the
place, and losing their properties in the process. I think the cap
value was OK but the ESR went sky-high.

Unfortunately I can't measure ESR with anything I have here...

The safest thing will be to rework all the circuits and change the
caps.

 

[Peter]

"[email protected]"

Do they work?? The ones I use look like that from the factory!

Yes, they work.