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December 15, 2016

Is Baking Required After Aqueous Cleaning?

Do assembled circuit board assemblies need to be baked after routine aqueous cleaning?

If so how long and at what temperature?

C. W.

Experts Comments

Ideally if the aqueous cleaning process takes place in an automated system, there should already be a drying stage, where the washed and rinsed assemblies are dried at a certain temparture and predetermined cycle time.

However if the drying in the equipment is not sufficient, we ahd experiences in the field where the client bakes the boards in a standalone dryer for 30 minutes at 140 degrees Fahrenheit. I

n order to find out whether the drying in your aqueous cleaning equipment is enough or not, you could conduct a simple test by taking a fully clean (flux-removed) populated assembly, weighing it before and after the aqueous cleaning process and observe the weight change.

If there is a significant weight increase then the dryers in the process may not be working properly that you would need to bake your board further in a stand alone oven.

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Umut Tosun
Application Technology Manager
Zestron America
Mr. Tosun has published numerous technical articles. As an active member of the SMTA and IPC organizations, Mr. Tosun has presented a variety of papers and studies on topics such as "Lead-Free Cleaning" and "Climatic Reliability".

The true answer is that some assemblies may require baking and some may not. It really depends on what type of machine is used for cleaning / drying.

If your cleaner utilizes airknifes that mechanically dry the assemblies, then your chances of a required bake process are increased, particularly with multi-layer boards. Airknifes are most commonly associated with inline cleaning systems.

If your cleaner utilizes a convection / radiant forced heat technology (common on higher-end batch cleaning systems), to dry the assemblies, then the answer is more likely no bake out is required.

One good tool to assess the "dryness" is to weight the assemblies before and after cleaning. In a thorough drying application, the assemblies should weigh less after cleaning than before cleaning.

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Mike Konrad
President
Aqueous Technologies
Mr. Konrad has been in the electronic assembly equipment industry since 1985. He is founder and CEO of Aqueous Technologies Corporation, a manufacturer of automatic de-fluxing equipment, chemicals, and cleanliness testing systems.

There are many elements or variables involved before making this decision. Two of them are related to the process and they are how wet are the boards when they exit the cleaning process, and what type of water was used in the final rinse, DI (Deionized), Distilled, or Tap water?

The other variable is: What is the time cycle between the time the product exits the equipment and the time it will be electrically tested.

If it is tested immediately then the boards must be dry. If the boards are wet coming out of the cleaner, the water can either be blown off with an air hose or allowed to evaporate from the surface of the board.

This is why I asked about the type of water being used in the final rinse as the minerals in the water will be left on the board if the water is allowed to evaporate, hence you need to use DI rinse to make sure there are no extra minerals and contaminants in the water which may impact the dielectric performance of the laminate material.

If the water is blown off then heating them will enhance the evaporation process and provide a dry board quite quickly. Then the boards can be baked for a couple of hours at 100 to 150F to dry the boards prior to going into electrical testing.

I must emphasize however that if the boards are dripping wet when coming out of the aqueous cleaner, it will take a much longer time to evaporate all the water from the surface of the boards and the time in the oven must be determined by the local plant environment, i.e., humidity controls, ventilation in the oven, in-line vs. batch dryers, etc.

If the product is being cleaned in an in-line aqueous cleaners the final blow off must be sufficient to remove all the excess water and the heating system must be sufficient to dry the boards of any excess water.

If they are coming out wet from the in-line system, the capability of the equipment must be questioned and the process should be adjusted to verify the equipment is capable of providing the end results expected, i.e., dry boards.

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Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

Your answer is generally no.

The vast majority of assemblies cleaned in an aqueous process, with or without cleaning materials beyond water alone, are dried but no baked out.

There are a host of special circumstances where bake outs are routinely performed, and the range of temperature and durations vary widely. I will leave it to those currently using bake outs to provide those specifics.

The key element here is that a very small percentage (I would estimate well below 10%) of assemblies seeing water in their cleaning process are followed by an "oven type" extended bake out.

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Tom Forsythe
Vice President
Kyzen Corporation
Mr. Forsythe is a recognized expert in cleaning chemistries and processes. Tom has a Bachelor's in Applied Mathematics & Engineering from the US Naval Academy. He is well published in both the industry trade magazines. Tom has spent the last 14 years with Kyzen Corporation.

Only if the board is going to be heated to reflow temperatures.

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Edward Zamborsky
Regional Sales Manager
OK International Inc.
Mr. Zamborsky serves as one of OK's technology advisers to the Product Development group. Ed has authored articles and papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.
If your boards are wet with liquid water you must dry them to pass electrical test. If your boards are free of liquid water, this is an equilibrium question which is dependent on the final environment in which they will be used. General rule is they should have less absorbed water than they will have in their operating environment.

To remove most absorbed water, a 2-4 hr bake at 105C or a 8-24hr bake at 65C is adequate for typical FR-4 type assemblies.
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Steve Stach
President
Austin American Technology
Founder and President of AAT. Steve holds numerous patents and has authored numerous research papers and articles in cleaning and soldering. Steve is a founding member of the Central Texas Electronics Association and is a past Director of IMAPS. Steve is active on several IPC cleaning committees.
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