Conformal Coatings - PCB Cleaning and Drying

GA JAE

In addition that process ought to be recognize/ be independent of the vagaries of ambient humidity temperature etc...or else should run for several standard deviations beyond the normal 'dry cycle' in best case.

milo only thing worse than cleaning is drying from a process control perspective

Hello,

I am new joinee to this site and found the information provided by you all very useful. I am re-opening the subject once again.We are using FR4 pcbs. I need your help in deciding some specs in drying process--at what temperature & for how much time we should heat the pcb assemblies prior to conformal coating? What is the time allowed once you take the hot pcbs out of the oven & coat it?

I agree with JaE.

Have you asked your flux supplier for assistance?

Do you visual after cleaning?

Take some test panels home with you, and _{WHEN YOUR WIFE'S GONE} run them through your dishwasher and find out. It should work fine. I used to build PCB fab equipment which was not much more than a 50-100 foot long plastic dishwasher.

DI rinse is good. Dry with clean, filtered de-ionised/static free air or centrifugal action, as JaE said. Compressor oil and water are both bad, too.

Drain your air tank daily to reduce moisture content.

Keep all silicone containing products in another isolated area. Silicone spray can travel for many, many feet. Doesn't sound like you have this problem, yet.

Good Luck! Welcome.

Lyn

Yes, a dish washer works great. Years ago I worked for Raytheon Computer in Santa Ana CA. We designed and built A/D and DACs. In those days, an Analog Multiplexer, Sample and Hold Amp and an A/D took up a whole 19" Rack. Now days it is 3 chips.

The Production line assembled 50 to 200 PCB's a day. They were all washed in dish washers (we had 3 of them) with DI water. They were oven dried and Conformal Coated. Later at another company I set up the conformal coating department for the production of Digital volt meters. These boards were washed by hand using real hot water (DI water) and liquid dish soap, oven dried and dip coated with Humiseal. Years later at a small start-up company (Western Digital) had a problem with washing Integrated Circuit Wafers. After testing many expensive soap cleaners formulated for wafer washing and other soaps, inspecting them for contaminants using an Electron Microscope, we found that Lemon Scented Joy was the absolute winner. Lemon Scented joy immediately was written into the process specifications for the production of IC's.

I have been using Lemon Scented Joy for PCB cleaning for over 30 years.

If you are interested, I'm sure I can find my PCB Process Spec used for Conformal coating. It may be old and dusty but I'm sure it is still works.

So JAE gets a GA for posting a link? You guys are pathetic.

Thanks for the critique. Sometimes I also feel that GA's are too easily awarded and there have been whole threads relating to exactly that.

I would hope that whoever it was that linked the GA to that response believed that the other information provided contributed to the initiators understanding of board cleaning, like the potential of multiple contaminants and the fact that what is causing issue today might not be the one that was there last week. Also the acknowledgement that as a "new" contributor their effort in describing the situation provided us with enough information to provide meaningful feedback.

I almost didn't include the link, since it might influence preference to a particular supplier that I know of and there may well be others more suited that I don't know of.

Your thoughts remind us that we need to remain serious about when we issue GA "rewards".

In one capacity or another, I was involved in PCB coating for 20 years.

The answer given was good. I have not looked at the link.

GA to you. Ga is not a reward. It's an acknowledgment that the answer has merit and helps solve a problem.

Sure...i agree, but there is no consistency. It seems (to me) that there are a few of the regulars that just keep passing these GA to each other - while others (often less contributive) that give great answers get non (no - i don't have a gripe on anything i've posted - just in case).

Hi Heath,

Plastic moisture sensitive components absorb moisture over time and should be placed in an oven for the time specified by the manufacturer of the components before installing them.

Bioact EC-7R Dfluxer is my favorite. Discerning what components should not be exposed to it and isopropyl alcohol is important of course.

For removing fluxes, conformal coatings, and most contaminants, dip and agitate the assemblies in a bath of BIOACT EC-7R Semi-Aqueous Defluxer (a patented blend of orange terpenes and aliphatic esters) for as much time as needed, typically 15 minutes, then 15 minutes in a bath of isopropyl alcohol followed by another 15 minutes in a second bath of isopropyl alcohol followed by drying in a flowing air chamber.

Establish a standard procedure for using the system and for replacing the solvents by visual inspection or specific gravity.

Time in the oven before conformal coating is applied and curing of the coating in the oven afterwards is a good procedure for keeping the product moving.

Finding a reasonably priced cleaning machine is not so easy. For a small operation wire baskets to hold the products in baths that use pneumatic pumps to circulate the solvents are a good idea. The same filtered air supply is used for the flowing air drying chamber.

The topic of moisture-sensitive components is rather boring but very important — and frequently misunderstood. Increased moisture-sensitive component use, such as thin fine-pitch devices and ball grid arrays (BGA), has increased concern for this failure mechanism. When components are exposed to the elevated temperatures that occur during reflow soldering, moisture trapped inside plastic surface mount devices (SMD) produces enough vapor pressure to damage or destroy the device. Common failure modes include internal separation (delamination) of the plastic from the die or lead-frame; wire bond damage; die damage; and internal cracks that do not extend to the component surface. In extreme cases, cracks will extend to the component surface; in the most severe cases, the component will bulge and pop (referred to as the "popcorn" effect).

I got some great replies from my question. I now have a much better idea for what I need to do. When I implement the new procedures, I'll post to this thread with the results.

This is a great site, I can't believe I have not come across it before.

thanks,

heath holcomb

Come on back! It's addictive. And there are some very intelligent people here.