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dirty boards

J

John Larkin

Jan 1, 1970
0
We sent out a batch of 35 VME module kits to be built by a contract
assembly house. There are lots of high-value resistors on this board

http://www.highlandtechnology.com/DSS/V360DS.html

in the filters and such. Boards started failing in test and it seems
to be caused by ionic contamination trapped under parts. The stuffers
used water-soluble flux (which is contrary to our rules) and obviously
didn't clean the boards enough. They claim to use a super
high-pressure conveyerized spray cleaner with super-clean water. I'm
skeptical about the cleanliness of their system, and they just told us
that the cleaning line "just broke" so now they can't rerun the
boards.

So, what's your experience? Can a water-soluble flux be reliably
cleaned off to decent leakage levels? Can they really clean under
surface-mount parts?

Last time this happened, some years ago with another assembler, we
nabbed a sample of their wash water, and it was 20x as conductive as
tap water.

I'm thinking in terms of slowly hand-scanning each board with a
water-pic sort of high-pressure wand, with single-use distilled water,
or something like that. It looks tricky to clean under surfmount
parts, especially with water. Our normal process is RMA flux followed
by solvent wash in a vapor degreaser.

Is there anything that can be added to the wash water to reduce its
surface tension, to get under parts better, but that isn't itself a
source of leakage? Maybe an alcohol/water mix?

Are there any lead-free implications as regards leakage? This board
uses regular pb/sn solder, but it may become a concerm some day.

John
 
K

Ken Smith

Jan 1, 1970
0
John Larkin said:
They claim to use a super
high-pressure conveyerized spray cleaner with super-clean water. I'm
skeptical about the cleanliness of their system, and they just told us
that the cleaning line "just broke" so now they can't rerun the
boards.

Did this "just broke" happen right after you complained about the PCBs adn
asked that they be rewashed?

If so, I'd start to suspect everything they've told you. Chances are it
really failed before your PCBs. It wouldn't suprise me to dicover that
they cleaned them with a crub brush and a bucket of water.

As far as I know the board house that did the last PCBs for me used what
is really a dishwasher with a different trim option. The trick seem to be
just to throw enough water at it for long enough.

So, what's your experience? Can a water-soluble flux be reliably
cleaned off to decent leakage levels? Can they really clean under
surface-mount parts?

The only flux I've really had trouble with was the "no clean" type. I
don't think it should ever be used.

Last time this happened, some years ago with another assembler, we
nabbed a sample of their wash water, and it was 20x as conductive as
tap water.

Using dirty solvent is trouble, whether or not it is water.
I'm thinking in terms of slowly hand-scanning each board with a
water-pic sort of high-pressure wand, with single-use distilled water,
or something like that. It looks tricky to clean under surfmount
parts, especially with water.


.... or ...
You could attach the PCBs to the wall and get 20 guys with fire hoses to
blast away at them for a day. If one squirt with water only lowers the
flux level by 10%, 1000 squirts will get the board clean.
Is there anything that can be added to the wash water to reduce its
surface tension, to get under parts better, but that isn't itself a
source of leakage? Maybe an alcohol/water mix?

I believe that there is a detergent of some sort added to the first wash.
After that it is washed with pure water.

Are there any lead-free implications as regards leakage? This board
uses regular pb/sn solder, but it may become a concerm some day.

A lead free soldered PCB will short out due to tin whiskers, so the ionic
stuff won't matter at all. :)

The unobtainium in the lead free flux may be harder to move.
 
J

John Popelish

Jan 1, 1970
0
John said:
We sent out a batch of 35 VME module kits to be built by a contract
assembly house. There are lots of high-value resistors on this board

http://www.highlandtechnology.com/DSS/V360DS.html

in the filters and such. Boards started failing in test and it seems
to be caused by ionic contamination trapped under parts. The stuffers
used water-soluble flux (which is contrary to our rules) and obviously
didn't clean the boards enough. They claim to use a super
high-pressure conveyerized spray cleaner with super-clean water. I'm
skeptical about the cleanliness of their system, and they just told us
that the cleaning line "just broke" so now they can't rerun the
boards.

So, what's your experience? Can a water-soluble flux be reliably
cleaned off to decent leakage levels? Can they really clean under
surface-mount parts?

Last time this happened, some years ago with another assembler, we
nabbed a sample of their wash water, and it was 20x as conductive as
tap water.

I'm thinking in terms of slowly hand-scanning each board with a
water-pic sort of high-pressure wand, with single-use distilled water,
or something like that. It looks tricky to clean under surfmount
parts, especially with water. Our normal process is RMA flux followed
by solvent wash in a vapor degreaser.

Is there anything that can be added to the wash water to reduce its
surface tension, to get under parts better, but that isn't itself a
source of leakage? Maybe an alcohol/water mix?

Are there any lead-free implications as regards leakage? This board
uses regular pb/sn solder, but it may become a concerm some day.

In one case, I successfully improved the leakage resistance of a board
with surface mount parts, but it didn't include a battery or any
electrolytic capacitors. I first soaked the board in warm 99% pure
isopropyl alcohol for an hour or so, to remove any covering of rosin
flux (some parts had been hand soldered), and then cooked the boards
for an hour or so in near boiling (perhaps 85 C) distilled water,
followed by a couple rinses in cold, clean distilled water.

I then baked the boards in a vacuum oven at 50 C, overnight, to make
sure all the surface bound water escaped.
 
J

John Larkin

Jan 1, 1970
0
In one case, I successfully improved the leakage resistance of a board
with surface mount parts, but it didn't include a battery or any
electrolytic capacitors. I first soaked the board in warm 99% pure
isopropyl alcohol for an hour or so, to remove any covering of rosin
flux (some parts had been hand soldered), and then cooked the boards
for an hour or so in near boiling (perhaps 85 C) distilled water,
followed by a couple rinses in cold, clean distilled water.

I then baked the boards in a vacuum oven at 50 C, overnight, to make
sure all the surface bound water escaped.

My real concern is leaving hygroscopic crud under the parts. If we
bake them dry, they'll pass test, but may well later suck moisture out
of the air and fail in the field.

We've never had any leakage problems with rosin flux. It's not
conductive whether you clean it or not.

John
 
Q

qrk

Jan 1, 1970
0
We sent out a batch of 35 VME module kits to be built by a contract
assembly house. There are lots of high-value resistors on this board

http://www.highlandtechnology.com/DSS/V360DS.html

in the filters and such. Boards started failing in test and it seems
to be caused by ionic contamination trapped under parts. The stuffers
used water-soluble flux (which is contrary to our rules) and obviously
didn't clean the boards enough. They claim to use a super
high-pressure conveyerized spray cleaner with super-clean water. I'm
skeptical about the cleanliness of their system, and they just told us
that the cleaning line "just broke" so now they can't rerun the
boards.

So, what's your experience? Can a water-soluble flux be reliably
cleaned off to decent leakage levels? Can they really clean under
surface-mount parts?

Last time this happened, some years ago with another assembler, we
nabbed a sample of their wash water, and it was 20x as conductive as
tap water.

I'm thinking in terms of slowly hand-scanning each board with a
water-pic sort of high-pressure wand, with single-use distilled water,
or something like that. It looks tricky to clean under surfmount
parts, especially with water. Our normal process is RMA flux followed
by solvent wash in a vapor degreaser.

Is there anything that can be added to the wash water to reduce its
surface tension, to get under parts better, but that isn't itself a
source of leakage? Maybe an alcohol/water mix?

Are there any lead-free implications as regards leakage? This board
uses regular pb/sn solder, but it may become a concerm some day.

John
Had this sort of thing happen in the mid 90's on a board with a hi-Z
(10Meg) node. We got on the assembly house's case and made sure they
gave the boards a final wash in a fresh batch of cleaner. I believe
they were using water soluble cleaner. Problem was contamination under
a SOT23 Schottky diode. In retrospect, I wonder if it would have
helped if the soldermask was removed under the part to give more
clearance between the underbelly of the part and the board?
 
P

Phil Hobbs

Jan 1, 1970
0
Ken said:
Did this "just broke" happen right after you complained about the PCBs adn
asked that they be rewashed?

If so, I'd start to suspect everything they've told you. Chances are it
really failed before your PCBs. It wouldn't suprise me to dicover that
they cleaned them with a crub brush and a bucket of water.

As far as I know the board house that did the last PCBs for me used what
is really a dishwasher with a different trim option. The trick seem to be
just to throw enough water at it for long enough.


Don't knock dishwashers. They work great. The problem is getting flux
out from under those high-value parts--it should happen eventually, but
you'll have to calibrate it. Try bringing a board home and running it
through your DW three or four times, first with detergent and then with
ordinary tap water.


Cheers,

Phil Hobbs
 
J

John Popelish

Jan 1, 1970
0
John said:
My real concern is leaving hygroscopic crud under the parts. If we
bake them dry, they'll pass test, but may well later suck moisture out
of the air and fail in the field.

Yes, you would want to soak them in the highest specified humidity
before testing, so the thorough dry out is probably pointless.
We've never had any leakage problems with rosin flux. It's not
conductive whether you clean it or not.

But ionic crud could have contaminated the surfaces before the hand
soldering added a layer of rosin. I had to remove the rosin before
the crud could be dissolved off with water.
 
J

John Larkin

Jan 1, 1970
0
The only flux I've really had trouble with was the "no clean" type. I
don't think it should ever be used.

I'll second that. It's nasty, greasy, dirty stuff, more like "can't
clean" flux. But the no-clean crud I've used doesn't seem to conduct.
Using dirty solvent is trouble, whether or not it is water.

Organic solvent loaded with a bit of rosin flux seems to be safe, if
not very cosmetic. Rosin residues don't seem to conduct. In our
in-house vapor degreaser, we submerge the board for a while in a
boiling solvent that has a deflux agent in it, then spray it down with
a wand that pumps clean, freshly-distilled solvent. The solvent wets
the pcb and parts, unlike water which beads.
... or ...
You could attach the PCBs to the wall and get 20 guys with fire hoses to
blast away at them for a day. If one squirt with water only lowers the
flux level by 10%, 1000 squirts will get the board clean.

We'd just need a distilled-water fire hydrant. I considered using my
big ole 1500 psi pressure washer, but it would use tap water, too.
Hence the dental water-pic idea, fillable with distilled or deionized
water, whichever ohms highest.

I just filled my red plastic Official Presidential Drinking Cup with
local tap water, and poked in a pair of standard Fluke probes 1"
apart, and got about 1.2 Mohms, not too bad. Same test with water from
the office cooler, Alhambra Mountain Spring Water, is about half that.


John
 
M

mc

Jan 1, 1970
0
The only flux I've really had trouble with was the "no clean" type. I
don't think it should ever be used.

What kind of trouble?
 
R

Rich Grise

Jan 1, 1970
0
We sent out a batch of 35 VME module kits to be built by a contract
assembly house. There are lots of high-value resistors on this board

http://www.highlandtechnology.com/DSS/V360DS.html

in the filters and such. Boards started failing in test and it seems
to be caused by ionic contamination trapped under parts. The stuffers
used water-soluble flux (which is contrary to our rules) and obviously ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
didn't clean the boards enough.


Dude, man up! If the boards don't meet your spec, they're rejects. Send
the boards back and tell the stuffer they don't get paid until the boards
are right, or make them pay for the rework.

Good Luck!
Rich
 
J

John Larkin

Jan 1, 1970
0
Dude, man up! If the boards don't meet your spec, they're rejects. Send
the boards back and tell the stuffer they don't get paid until the boards
are right, or make them pay for the rework.

We own the boards and the parts, and customers are waiting for
delivery. The only thing we can do to the vendor is not pay them for
assembly and never use them again. Meanwhile, the problem has to be
fixed.

John
 
S

Spehro Pefhany

Jan 1, 1970
0
I'm thinking in terms of slowly hand-scanning each board with a
water-pic sort of high-pressure wand, with single-use distilled water,
or something like that. It looks tricky to clean under surfmount
parts, especially with water. Our normal process is RMA flux followed
by solvent wash in a vapor degreaser.

Last (and only) time I had this problem, cleaning the boards using
solvent scrub in the critical area worked. The crud was quite
difficult to remove, a simply solvent wash was not enough. But in our
case, I think it was on the surface-- a nasty hydrophilic (?) layer of
something, rather than underneath the parts. Try axing the chemical
manufacturers, they are generally pretty good (at least I've had good
luck with Kester).


Best regards,
Spehro Pefhany
 
J

John Popelish

Jan 1, 1970
0
John said:
We'd just need a distilled-water fire hydrant. I considered using my
big ole 1500 psi pressure washer, but it would use tap water, too.
Hence the dental water-pic idea, fillable with distilled or deionized
water, whichever ohms highest.

I just filled my red plastic Official Presidential Drinking Cup with
local tap water, and poked in a pair of standard Fluke probes 1"
apart, and got about 1.2 Mohms, not too bad. Same test with water from
the office cooler, Alhambra Mountain Spring Water, is about half that.

You need distilled water only for the final spray rinse to displace
the film of tap water. Tap water is fine to remove the vast majority
of the contamination.
 
R

RST Engineering \(jw\)

Jan 1, 1970
0
I've had reasonable luck with an ultrasonic tank filled with the appropriate
solvent. I'd probably wash in a mild soap and water solution followed by a
rinse in distilled.

Tequila would probably work also {;-)

Jim
 
M

Mike Monett

Jan 1, 1970
0
John Larkin said:
My real concern is leaving hygroscopic crud under the parts. If we
bake them dry, they'll pass test, but may well later suck moisture out
of the air and fail in the field.

We've never had any leakage problems with rosin flux. It's not
conductive whether you clean it or not.

John

John,

Here are some posts I collected from Bob Wilson on cleaning flux
from pcb's. His comment on activator salts leaving a white residue
being dynamite is absolutely correct. I ruined a perfectly good dvm
by trying to clean it after it started acting up in high humididy.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Subject: Re: Flux cleaning ?
Date: 2001-10-09 16:16:48 PST

Dave Rosenbloom wrote:
Have you had any problems with it attacking plastic parts?

Never mind fooling around with stuff whose solvency you don't
understand. Partial or incorrect removal of resin based flux is FAR
worse than doing nothing at all.

Resin fluxes require both polar and nonpolar solvents to remove all
components completely. Using a bit of solvent (even the correct
blend) and a brush, is REALLY bad news. What is mainly does is just
spread the flux around all over the place.

There are 2 main ingredients in resin fluxes. First, there is the
resin itself. The active ingredient in resin is Abetic Acid. Resin
requires a nonpolar sovent to remove it (such as trichloroethane, or
even toluene).

The other ingredient is the activator salts (typically chlorides and
fluorides). These are soluable in a polar solvent ONLY (such as
isopropanol, or even water). They are ABSOLUTELY UNAFFECTED by the
nonpolar solvents that will dissolve the resin component.

Attempting to use Disc Brake cleaner, or any other aggressive
NON-polar solvent will simply remove the protective resin (that
previously and harmlessly encapsulated the hygroscopic and
conductive activator salts), and expose these salts to the air. This
results in high impedance conductive paths all over the PCB, and
possible corrosion.

You cannot see the activator salts, in most cases, but in higher
concentrations they do appear as a slight white residue. This is
dynamite!

So before anyone uses whatever snake oil thay happen to find laying
around, it is wise to understand the chemistry that underlies this
operation.

For years an excellent flux remover was a 30% mixture of isopropyl
alcohol, with the remaining 70% being trichloroethane or freon.
Since both trichloroethane and freon are no longer easily available,
a good substitute is plain ordinary "lacquer thinner" (mainly
toluene). This mixture will remove ALL parts of the flux. Pure 99%
Isopropanol (aka "rubbing alcohol") WILL work as well, since it DOES
dissolve both polar and non polar residues, BUT it is extremely slow
to dissolve the non-polar stuff (resin). The above mixture acts much
faster,and still does not harm most components (polystyrene caps are
the exception, but they dissolve in nearly anything anyway).

The other alternative is to remove the resin based flux with a
proprietry Saponifier in a water solution (Kester makes one). This
requires very strong agitation, and hot water/saponifier solution.

Finally, one can just use water-soluable-flux solder. Some brands so
not have very good "fluxing" action, although I have had good luck
with the stuff made by Alpha Metals. Warm, HIGH PRESSURE water spray
(to get under ICs and so on) is a must to remove this. One good way
is to stick the PCBs in a dishwasher. Personally, I use water
soluable flux wherever possible. It works well and DOES remove
completely. One final point: you must ALWAYS clean water soluable
flux off the PCB. NEVER leave it on there. It is extremely
hygrosopic and will result is a malfunctioning PCB after it has
absorbed atmospheric water (1 to 4 weeks later).

Bpb.

You need a solvent blend that contains both ionic and non-ionic
solvents. A very good blend is 70% trichloroethane and 30%
isopropanol (isopropyl, or "rubbing" alcohol). The trichlorethane is
an aggrressive non-ionic solvent and the isopropanol attacks the
ionic salts.

Although isopropanol is a drugstore item, trichloroethane is not. If
you have a problem with this, xylene or toluene (or even ordinary
lacquer) can be used instead, although these are more aggressive
solvents and some parts may be affected (test first). Increasing the
proportions to 50-50 will reduce the aggressiveness of the blend.

Even straight isopropanol can be used, since it can dissolve bothe
ionic and non-ionic residues. However it is a very feeble non-ionic
solvent, so it will take a long time to attach the resin and other
non-ionic residues.

Be sure to immerse the PCB in a reasonable volume of solvent, and
rinse in a fresh bath. **Use lots!!** DO NOT JUST SWAB IT AROUND
WITH A COTTON SWAB!!! All this will do is to spread the flux all
over the place, and partially dissolve the rosin, exposing the
activator salts that were previously trapped harmlessly. EITHER
CLEAN THE PCB PROPERLY OR NOT AT ALL!

BOb.

Naptha would work well if the crud were purely non-ionic, however I
suggested the Full Monte cleaning because the true makup of the crud
was not known, and also because there will CERTAINLY be some small
amount of flux residue if the motherboard were made in the orient
(which most are).

You are correct that there is no rule that a solvent mix must be
used. Sequential cleaning (as long as the rosin is removed first to
expose the activators) is perfectly acceptable.

I agree with Bob. Most of the flux is no clean today. Why use an
extra processing step (washing) if you don't need to. Especially
when you have some non-washable parts on the board.

Now, I use a turpine based solvent that:

1) Smells great (it is orange peeling oil really)
2) Is predominantly non-toxic and non polluting.
3) Most importantly, does a great job in cleaning the boards.

The only drawback is that it takes a long time (when compared to
freon) to evaporate. If you use compressed air to get the majority
of it off, then it will dry in a few minutes. It does a great job
and if used in liberal quantities and some scrubbing, leaves no
residue. That cannot usually be said about acohols and freon based
solvents.

Chuck

I agree, that clean water wash is good if all the components are
sealed. Another method that does not require careful drying is to
use a turpine (orange/lemon peeling oil) based solvent. It smells
good, cleans good, takes a while to evaporate (I suggest using
compressed air) and leaves very little or no residue. It will eat
styrene but that is the only plastic that I have found that it
doesn't like. BTW never use any type of alcohol on poly carbonate
components. Like the plugs on the ends of phone cords.

Chuck

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Regards,

Mike Monett
 
L

Leon

Jan 1, 1970
0
John said:
We own the boards and the parts, and customers are waiting for
delivery. The only thing we can do to the vendor is not pay them for
assembly and never use them again. Meanwhile, the problem has to be
fixed.

Try scrubbing them with cellulose thinners (xylene) followed by IPA. I
find that works very well on all types of flux.

Leon
 
M

Martin Riddle

Jan 1, 1970
0
John Larkin said:
We sent out a batch of 35 VME module kits to be built by a contract
assembly house. There are lots of high-value resistors on this board

http://www.highlandtechnology.com/DSS/V360DS.html

in the filters and such. Boards started failing in test and it seems
to be caused by ionic contamination trapped under parts. The stuffers
used water-soluble flux (which is contrary to our rules) and obviously
didn't clean the boards enough. They claim to use a super
high-pressure conveyerized spray cleaner with super-clean water. I'm
skeptical about the cleanliness of their system, and they just told us
that the cleaning line "just broke" so now they can't rerun the
boards.

So, what's your experience? Can a water-soluble flux be reliably
cleaned off to decent leakage levels? Can they really clean under
surface-mount parts?
I would guess not, We had a simlar problem with a crystal and residue
under it from the water cleaning process.
Last time this happened, some years ago with another assembler, we
nabbed a sample of their wash water, and it was 20x as conductive as
tap water.
They all seem to be aware of the problem
I'm thinking in terms of slowly hand-scanning each board with a
water-pic sort of high-pressure wand, with single-use distilled water,
or something like that. It looks tricky to clean under surfmount
parts, especially with water. Our normal process is RMA flux followed
by solvent wash in a vapor degreaser.

Is there anything that can be added to the wash water to reduce its
surface tension, to get under parts better, but that isn't itself a
source of leakage? Maybe an alcohol/water mix?
We tried a alcohol wash after the fact, and the crap was still under the
crystal. It seem that once it dries its very tuff to wash out. John P's
wash and rinse might work.
I would recomend a Milled slot under the part in the next design,
similar to HV stuff.
Are there any lead-free implications as regards leakage? This board
uses regular pb/sn solder, but it may become a concerm some day.
Wiskers, selective conformal coating time.


Cheers
 
K

Ken Smith

Jan 1, 1970
0
I'll second that. It's nasty, greasy, dirty stuff, more like "can't
clean" flux. But the no-clean crud I've used doesn't seem to conduct.

I've seen it conduct and ruin PCBs. The environment was full of decane
though so that may be a special case.
We'd just need a distilled-water fire hydrant.

Actually, you could use ordinary tap water in most places and then follow
with a distilled-water bath.
I just filled my red plastic Official Presidential Drinking Cup with
local tap water, and poked in a pair of standard Fluke probes 1"
apart, and got about 1.2 Mohms, not too bad. Same test with water from
the office cooler, Alhambra Mountain Spring Water, is about half that.

In almost every place in North America, tap water is the way to go for
both washing and drinking.
 
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