|Ask the Experts|
July 3, 2018
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?
|Expert Panel Responses|
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.
Application Technology Manager
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.
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.
Vice President, Technical Director
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.
Only if the board is going to be heated to reflow temperatures.
Regional Sales Manager
OK International Inc.
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.
Austin American Technology
The answer is yes! If you clean in especially an ultrasonic cleaner as the cavitation guarantees penetration throughout the entire board. Trust me you will blow shit up if you do not follow a standard procedure.Joe Peka
After cleaning in water and solution it is recommended to spray rinse the board in fresh demineralised water to clean solution. It then gets put into a bath of 100% isopropyl alcohol as it naturally displaces water. After about a minute remove board from iso and blow access with compressed air. Only then it should go into a preheated 100c oven as this is the boiling temp of water yet not hot enough to reflow or burn plastic. I recommend 1 hour in the oven then half an hour with oven off to allow safe cooling as the rapid change in temp can cause fractures and chip creep.
When we receive chips or components the manufacturer advises to put in oven for 24 hours but I'm not wasting power when my method is proven to work.
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