Voids in solder joint under high environmental pressure

[Rune]

Hi, Anyone have any clues on judging voids in solder joints for cyclic
high pressure applications(0 -350 bar, 0-5000 PSI)? More specific how
would a 0.1mm3 gas pocket under a D2pack on FR4 laminate with 135u
copper layer affect that solder joint if environmental pressure is
cycled between 0 and 350 bar?

Best regards,

Rune

 

[George Herold]

Hi, Anyone have any clues on judging voids in solder joints for cyclic
high pressure applications(0 -350 bar, 0-5000 PSI)? More specific how
would a 0.1mm3 gas pocket under a D2pack on FR4 laminate with 135u
copper layer affect that solder joint if environmental pressure is
cycled between 0 and 350 bar?

Best regards,

Wow! 5,000 psi! I don't have a clue. Are you seeing failures of something. I guess I'd also worry about the bulk modulus differences of the various materials. So calculate how much strain you get from just bulk modulus differences and compare that to the strain from a little gas bubble. Which is bigger?

George H.

 

[Spehro Pefhany]

Wow! 5,000 psi! I don't have a clue. Are you seeing failures of something. I guess I'd also worry about the bulk modulus differences of the various materials. So calculate how much strain you get from just bulk modulus differences and compare that to the strain from a little gas bubble. Which is bigger?

George H.

Assuming the void is low pressure, everything should be compression,
at least. It might be okay, but WAG it's not with a lot of margin- a
0.5mm x 0.5mm void would result in the surrounding material carring ~
1kg force.

Since this is such a speciaized problem, if I couldn't find anyone
who'd done tests, I think I'd slap together an FEA analysis in
Solidworks or NASTRAN and see how it looks. The material
characteristics should be available.


Best regards,
Spehro Pefhany

 

[RobertMacy]

Hi, Anyone have any clues on judging voids in solder joints for cyclic
high pressure applications(0 -350 bar, 0-5000 PSI)? More specific how
would a 0.1mm3 gas pocket under a D2pack on FR4 laminate with 135u
copper layer affect that solder joint if environmental pressure is
cycled between 0 and 350 bar?

Best regards,

Rune

To prevent voids in our compounds wrapped around electronics, we used to
epoxy them in low atmospheric pressure, 10-3 torr [approx Bell Jar] where
we would watch with surprise at how they foamed like crazy before settling
down.

Perhaps, the soldering should be done in rarified atmosphere also, then
your question would become a moot point.

On a slightly related note, I once watched a spate of failures in high
power NPN transistors, TO-3 cans, used to drive high power ultrasonic
cleaners. The final resolve was that the IC Mfgr had allowed an increase
in voids under the die when mounting to the package - result: less thermal
conductivity and massive high temp failures. Thankfully it was their
quality issue and no need to change the design.

 

[RobertMacy]

Hi, Anyone have any clues on judging voids in solder joints for cyclic
high pressure applications(0 -350 bar, 0-5000 PSI)? More specific how
would a 0.1mm3 gas pocket under a D2pack on FR4 laminate with 135u
copper layer affect that solder joint if environmental pressure is
cycled between 0 and 350 bar?

Best regards,

Rune

To prevent voids in our compounds wrapped around electronics, we used to
epoxy them in low atmospheric pressure, 10-3 torr [approx Bell Jar]
where we would watch with surprise at how they foamed like crazy before
settling down.

Perhaps, the soldering should be done in rarified atmosphere also, then
your question would become a moot point.

On a slightly related note, I once watched a spate of failures in high
power NPN transistors, TO-3 cans, used to drive high power ultrasonic
cleaners. The final resolve was that the IC Mfgr had allowed an increase
in voids under the die when mounting to the package - result: less
thermal conductivity and massive high temp failures. Thankfully it was
their quality issue and no need to change the design.

sorry to answer my own, but forgot! Is this solder ROSH????

Again, slightly related, back in 70's plastic IC's shipped from Bay Area
to LA had a huge failure rate. The packages went by AIR, went through high
altitude where the packages tended to equalize, then on landing the
packages tended to 'suck' in the air, the smog from LA infused back in,
ate up the IC's and thus large failure rate.

Lesson here? Depending on rate of compression and decompression you may
have problems. Envision the void becoming higher pressure, then when
decompressed outside the void now has energy to try and blow the chip off.
From memory solder is pretty good under compression, but lousy under
tension [breaks] and ROSH compliant solder is worst!

 

[Rune]

Wow! 5,000 psi! I don't have a clue. Are you seeing failures of
something.
I guess I'd also worry about the bulk modulus differences of the >various
materials. So calculate how much strain you get from just bulk modulus
differences and compare that to the strain from a little gas bubble. Which is bigger?

George H.

Hi,
Thanks, god point, I must admit I have not considered the strain from
the bulk modulus differences in the various involved materials. I
suspect that will be a larger concern than the small voids in the solder
joints. For the same reason encapsulating this in a hard Polyurethane
potting material, as initially intended, and the surface mount D2pack
probably is a no go to? I need some more calculations on this. Maybe a
softer potting material would work better?

To save complexity, I would prefer not to go the oil and pressure
compensation route on this design.. This is not a realized application
yet but the circuit is intended to be used in a subsea installation
rated for 350 bar.

The gas pockets or voids was discovered by an x-ray inspection and after
some googling I find that this is a common issue especially for larger
solder pads the gas forms from the flux used in the solder paste.

Best regards,
Rune

 

[Rune]

No idea of the physical effect, but with such pressures and combustible
materials I would also be concerned if the gas had any oxidant or
reducing properties. I would expect oils and plastics to spontaneously
burn under oxygen at these pressures!

I have not considered that. Any reason to believe that there is any
significant amount of oxidizer in the gas formed form the solder paste?

Regards,
Rune

 

[Rune]

Hi, Anyone have any clues on judging voids in solder joints for
cyclic high pressure applications(0 -350 bar, 0-5000 PSI)? More
specific how would a 0.1mm3 gas pocket under a D2pack on FR4 laminate
with 135u copper layer affect that solder joint if environmental
pressure is cycled between 0 and 350 bar?

Best regards,

Rune

To prevent voids in our compounds wrapped around electronics, we used
to epoxy them in low atmospheric pressure, 10-3 torr [approx Bell Jar]
where we would watch with surprise at how they foamed like crazy
before settling down.

We use to vacumise the potting fluid before pouring it into the mold
Yes it does actually exist some reflow ovens that solders under vacum,
mostly used for outer space applications, unfortunately can't afford one.
yes I wish those component manufacturers would provide some more
available data of what kind of voids one can expect inside their potting
material. It's kind of a gamble until you get your hand on a X-ray
machine at least.

sorry to answer my own, but forgot! Is this solder ROSH????

No ROSH

Again, slightly related, back in 70's plastic IC's shipped from Bay Area
to LA had a huge failure rate. The packages went by AIR, went through
high altitude where the packages tended to equalize, then on landing the
packages tended to 'suck' in the air, the smog from LA infused back in,
ate up the IC's and thus large failure rate.

Nice. Thats an interesting way to measure pollution.

Lesson here? Depending on rate of compression and decompression you may
have problems. Envision the void becoming higher pressure, then when
decompressed outside the void now has energy to try and blow the chip
off. From memory solder is pretty good under compression, but lousy
under tension [breaks] and ROSH compliant solder is worst!

Good point, maybe I will have to go for a TO247 package or something
instead.

No ROSH, all lead and tinn here.
Best regards,
Rune

 

[John Devereux]

I have not considered that. Any reason to believe that there is any
significant amount of oxidizer in the gas formed form the solder
paste?

I can't see it being a real issue. These pressures are routine (if at
the high end) for normal industrial hydraulics, using flammable mineral
oil and tanks open to atmosphere. It happens all the time that fluid
gets aerated and then compressed etc.

 

[Robert Baer]

Hi, Anyone have any clues on judging voids in solder joints for cyclic
high pressure applications(0 -350 bar, 0-5000 PSI)? More specific how
would a 0.1mm3 gas pocket under a D2pack on FR4 laminate with 135u
copper layer affect that solder joint if environmental pressure is
cycled between 0 and 350 bar?

Best regards,

Rune

Find a way to Pick & Place SMDs with spacing between bottom of SMD
and board; maybe a thin sheet of sugar or other rather soluble material.
Do this with all of them!!!

 

[Robert Baer]

Wow! 5,000 psi! I don't have a clue. Are you seeing failures of something. I guess I'd also worry about the bulk modulus differences of the various materials. So calculate how much strain you get from just bulk modulus differences and compare that to the strain from a little gas bubble. Which is bigger?

George H.

What may be worse,is the integrity of the molded plastic packages!

 

[George Herold]

Which is bigger?
Hi,
Thanks, god point, I must admit I have not considered the strain from
the bulk modulus differences in the various involved materials. I
suspect that will be a larger concern than the small voids in the solder

That was sorta my 'gut feeling' but I really don't know! (Dang, I sometimes hate it when people think my advise is useful... I guess it's mostly whenI don't really know what I'm talking about.) I assume there are others here who have perhaps done some underwater circuits and will advise.

joints. For the same reason encapsulating this in a hard Polyurethane
potting material, as initially intended, and the surface mount D2pack
probably is a no go to? I need some more calculations on this. Maybe a
softer potting material would work better?

Is the potting to keep the water out?

Well this reminds me of differential thermal expansion.
(I wonder how the numbers compare?) I've got this project that's been "on hold" for a while now. But I'd like to use little surface mount components at low temperatures. I've been told that they aren't reliable.. but of course I want to try some testing of my own. (I haven't done it yet so I can't say much more.)
In your case, if it's possible, I might try through hole components. The leads can flex a little and take up any strain.

To save complexity, I would prefer not to go the oil and pressur
compensation route on this design.. This is not a realized application
yet but the circuit is intended to be used in a subsea installation
rated for 350 bar.

So have you done underwater circuit before?
Maybe there's an engineer in your group, that has made all these mistakes already? (So you don't have to :^)

George H.

 

[Robert Baer]

Hi,
Thanks, god point, I must admit I have not considered the strain from
the bulk modulus differences in the various involved materials. I
suspect that will be a larger concern than the small voids in the solder
joints. For the same reason encapsulating this in a hard Polyurethane
potting material, as initially intended, and the surface mount D2pack
probably is a no go to? I need some more calculations on this. Maybe a
softer potting material would work better?

* Potting, unless gone properly will create more problems,guaranteed.
And you will have to evaluate strength of materials, resilience, etc...

To save complexity, I would prefer not to go the oil and pressure
compensation route on this design.. This is not a realized application
yet but the circuit is intended to be used in a subsea installation
rated for 350 bar.

The gas pockets or voids was discovered by an x-ray inspection and after
some googling I find that this is a common issue especially for larger
solder pads the gas forms from the flux used in the solder paste.

* Oh. I mistakenly presumed you were talking of gas pockets under a SMD
package (where the idea i proposed would be useful).
Gas pockets from solder paste would be a big issue.

All surfaces that need soldering should then be de-oxidized by
something that can be totally removed,leaving a perfectly clean surface.
Then solder / paste WITHOUT organic (or other "activators") should be
used.
All of this in an inert atmosphere (helium in extreme) until have
finished product.
Makes no difference in those needs using tin/lead or RoHS tin/silver.
BTW, do NOT use pissy SAC which can cause problems.
For RoHS, PCBs are produced with immersion SILVER so the surface to
be soldered is SILVER and NOT copper; having copper alloyed in a solder
is counter-productive.
Some idiot took the GOOD idea of copper alloyed tin/lead solder to
create Savbit which prevented alloying copper from the soldering irons
(bits) and transformed it into the BAD idea of SAC.
Do not need copper: PCB surface is SILVER, solder is placed where
needed in paste form,and then re-flowed. Where is the bit / beef?

In small-scale hand production, (nickel coated?) iron bits are used;
NO copper.

End of rant.

 

[Robert Baer]

I have not considered that. Any reason to believe that there is any
significant amount of oxidizer in the gas formed form the solder paste?

Regards,
Rune

"Activators" in pastes are formulated to remove oxides and sulfides
and almost all are organic (read: reactive).
NOT oxidizer; that would be counter-productive.

 

[Robert Baer]

Hi, Anyone have any clues on judging voids in solder joints for
cyclic high pressure applications(0 -350 bar, 0-5000 PSI)? More
specific how would a 0.1mm3 gas pocket under a D2pack on FR4 laminate
with 135u copper layer affect that solder joint if environmental
pressure is cycled between 0 and 350 bar?

Best regards,

Rune


To prevent voids in our compounds wrapped around electronics, we used
to epoxy them in low atmospheric pressure, 10-3 torr [approx Bell Jar]
where we would watch with surprise at how they foamed like crazy
before settling down.

We use to vacumise the potting fluid before pouring it into the mold
Yes it does actually exist some reflow ovens that solders under vacum,
mostly used for outer space applications, unfortunately can't afford one.

* Flowing nitrogen, argon or helium allowa the use of a more
conventional reflow oven.

yes I wish those component manufacturers would provide some more
available data of what kind of voids one can expect inside their potting
material. It's kind of a gamble until you get your hand on a X-ray
machine at least.

sorry to answer my own, but forgot! Is this solder ROSH????

No ROSH

Again, slightly related, back in 70's plastic IC's shipped from Bay Area
to LA had a huge failure rate. The packages went by AIR, went through
high altitude where the packages tended to equalize, then on landing the
packages tended to 'suck' in the air, the smog from LA infused back in,
ate up the IC's and thus large failure rate.

Nice. Thats an interesting way to measure pollution.

Lesson here? Depending on rate of compression and decompression you may
have problems. Envision the void becoming higher pressure, then when
decompressed outside the void now has energy to try and blow the chip
off. From memory solder is pretty good under compression, but lousy
under tension [breaks] and ROSH compliant solder is worst!

Good point, maybe I will have to go for a TO247 package or something
instead.

No ROSH, all lead and tinn here.
Best regards,
Rune

 

[George Herold]

This reference:
http://www.fujitsu-ten.com/business/technicaljournal/pdf/33note2.pdf

suggests that a fractional strain of 1% gives a fatigue life of 1000

Real numbers! Phil you "da Man".
Where did you get the 1% from? Is it from figure 2?
I'm not sure how to read figure 2.
1000 fatigue life at delta_epsilon = 0.1... isn't that 10%, which seems like an outrageous strain... so maybe it's 0.1%? that seems like a more reasonable number.

As a point of reference (at least for moi) the thermal contraction from 300 to 77K is a few parts in 10^4 for many materials (nylon and teflon are worse.) (below 77K things don't contract much anymore.)

The Youngs modulus of FR4 is ~3E6 psi (if you can believe wiki)
http://en.wikipedia.org/wiki/FR-4

Which seems to imply that 5000 psi is about the same as thermal cycling to 77K (But I'd have to go and relearn Bulk modulus, Youngs modulus, poissins ratio and all that.)

George H.

 

[George Herold]

As a point of reference (at least for moi) the thermal contraction from 300 to 77K is a few parts in 10^4 for many materials (nylon and teflon are worse.) (below 77K things don't contract much anymore.)

Oops! No! a few parts in 10^3!
(what's a factor of ten mistake amongst friends?)

 

[[email protected]]

Go to Harbor Freight and get one of their hand operated hydraulic pumps.
If memory serves, these produce up to 10,000 psi. A bottle of fluid & a
steel block with a suitable hole would produce a test chamber.

Hul

Hi, Anyone have any clues on judging voids in solder joints for
cyclic high pressure applications(0 -350 bar, 0-5000 PSI)? More
specific how would a 0.1mm3 gas pocket under a D2pack on FR4 laminate
with 135u copper layer affect that solder joint if environmental
pressure is cycled between 0 and 350 bar?

Best regards,

Rune


To prevent voids in our compounds wrapped around electronics, we used
to epoxy them in low atmospheric pressure, 10-3 torr [approx Bell Jar]
where we would watch with surprise at how they foamed like crazy
before settling down.

We use to vacumise the potting fluid before pouring it into the mold

Yes it does actually exist some reflow ovens that solders under vacum,
mostly used for outer space applications, unfortunately can't afford one. yes I wish those component manufacturers would provide some more
available data of what kind of voids one can expect inside their potting
material. It's kind of a gamble until you get your hand on a X-ray
machine at least.

sorry to answer my own, but forgot! Is this solder ROSH????
No ROSH
Again, slightly related, back in 70's plastic IC's shipped from Bay Area
to LA had a huge failure rate. The packages went by AIR, went through
high altitude where the packages tended to equalize, then on landing the
packages tended to 'suck' in the air, the smog from LA infused back in,
ate up the IC's and thus large failure rate.

Nice. Thats an interesting way to measure pollution.

Lesson here? Depending on rate of compression and decompression you may
have problems. Envision the void becoming higher pressure, then when
decompressed outside the void now has energy to try and blow the chip
off. From memory solder is pretty good under compression, but lousy
under tension [breaks] and ROSH compliant solder is worst!

Good point, maybe I will have to go for a TO247 package or something
instead.

 

[Glen Walpert]

Hi,
Thanks, god point, I must admit I have not considered the strain from
the bulk modulus differences in the various involved materials. I
suspect that will be a larger concern than the small voids in the solder
joints. For the same reason encapsulating this in a hard Polyurethane
potting material, as initially intended, and the surface mount D2pack
probably is a no go to? I need some more calculations on this. Maybe a
softer potting material would work better?

To save complexity, I would prefer not to go the oil and pressure
compensation route on this design.. This is not a realized application
yet but the circuit is intended to be used in a subsea installation
rated for 350 bar.

The gas pockets or voids was discovered by an x-ray inspection and after
some googling I find that this is a common issue especially for larger
solder pads the gas forms from the flux used in the solder paste.

Best regards,
Rune

Some solder pastes have much lower tendency to produce voids than others,
you might want to search for low voiding solder pastes to minimize the
problem (although I have mostly seen these advertised for lead-free; tin
lead has become a low production niche product with far fewer options).

You might also consider pressure testing to a higher pressure,
hydrostatic test pumps are readily available to 10,000 psi and over at
reasonable prices, for example:

<http://www.hydro-test.com/ecommerce/hydrostatic-testing-equipment/air-
operated-test-pump.html?p=1>

Short term hydrotest pump rentals are also available.

If your device is small a test chamber could be quite simple, for example
a piece of heavy wall steel tubing closed with plates held by segmented
rings in a groove and sealed with o-rings.

Best regards,
Glen

 

[George Herold]

Well, that makes two of us. Somehow I was reading 0.1 as .01. That
makes all the numbers go up by two orders of magnitude, to some millions
of cycles if you believe they scale that far.
Or down if it's a percentage.
Generally there is some threshold strain below which fatigue failure
doesn't occur no matter how many cycles you give it.

Hmm, at the elastic limit (EL)? I'm not sure what the EL is.
At a guess when you start making dislocations in the lattice.
I should be able to do a Purcell, back of the envelope, calculation
(Binding energy of one atom to another.. over an atomic distance?)
I'll have to think about it.

George H.