Bev,
Your reply has prompted me to do a wee bit of reading. The article https://emsnow.com/time-retire-rose-testing-whether-cleanliness-test-process-control-tool/ supports my theory that ROSE is for 1970's designs and should be changed to support the fine pitch and high density of today's designs, but how and to what value is considered acceptable. So for a lack of a better definition I use the 1.56 ėg of NaCl eq. / cm2 as a target in my documentation.
Now let me answer all your questions.
You say presumed problematic. How solid is that presumption? Any evidence?
Sometimes it is a knee jerk solution to which I do not always agree, suspecting it is other process related issues such as heat exposure during wave solder. Placing small caps and resistors on the same board with very large inductors, large can electrolytic capacitors and heavy trace width and thickness is less than ideal design practice (power converter boards for 10+ kW units) in my opinion. And sometimes it is from manufacturer dissection and report of water ingress from Bourns, Avago, TI and others.
Why machine wash at all? Why not used a fully qualified no-clean and leave
it at that? Or are you building for space, medical or military? Or do the
optos require it?
We manufacture high voltage power supplies from 500 v to 180 kV for security inspection of airport baggage, commercial and medical lasers and semi-conductor manufacturing equipment.. Our sister division makes flash lamps running around 10 kV. The low residue (no-clean) flux can create a tracking failure mode. The data sheets for the optos demand halide free flux and the manufacturer states that the seal of the leads is different than your standard molded IC package thus potentially allowing ingress of flux or wash water.
For your CMs how are you setting the cleanliness standard? ROSE (yuck),
modified ROSE (yuck again), SIR/ECM?, ion chromatography?
A bit of a chuckle here. Our choice of CMs is often driven by cost not the Q word. We had one CM that washed the finished boards in a tub of plain water. We had to explain cleanliness to them.
Thanks, I hope these answers fill in the blanks for you.-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Saturday, June 20, 2020 10:32 AM
To: [log in to unmask]
Subject: Re: [TN] installing and hand washing as a final step
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Phil,
Aren't "cans of worms" TechNet's bread and butter?
You say presumed problematic. How solid is that presumption? Any evidence?
Why machine wash at all? Why not used a fully qualified no-clean and leave
it at that? Or are you building for space, medical or military? Or do the
optos require it?
For your CMs how are you setting the cleanliness standard? ROSE (yuck),
modified ROSE (yuck again), SIR/ECM?, ion chromatography?
Regards,
Bev
-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Nutting, Phil
Sent: June 20, 2020 10:04 AM
To: [log in to unmask]
Subject: [TN] installing and hand washing as a final step
Hi All,
I hope you have all been able to avoid becoming ill.
We have found some components (presumed) to be problematic when machine
washed. Avago optos, TI PTH logic (yes, we still do thru-hole), film
capacitors, trim pots and some other components are usually the offending
parts. These components are then designated to be hand installed, soldered
and washed after the boards are machine installed, solder and washed.
I fear the '70s are coming back.
About 80% of our PTH boards and 100% of our SMT boards are built by CMs. We
do not specify solder, flux or cleaning systems. We do however specify
lead-free and a cleanliness standard. In-house PTH boards are washed in a
closed loop batch DI washer.
I'm not a fan of switching to hand solder and wash for the simple reasons of
hand soldering is less consistent and hand cleaning may just spread residue
to a wider area.
I know I'm possibly opening a can of worms for process control, water
pressure, wash chemicals, choice of flux/paste. Is this a common
manufacturing solution? To me this is like fingernails on a chalkboard.
Phil Nutting | HVP Senior Development Engineer | Excelitas Technologies
Corp
Lab: +1 978.224.4332 | Office: +1 978.224.4152
35 Congress St, Salem, MA 01970 USA
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