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Baking assemblies after ultrasonic water wash

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#59033

Baking assemblies after ultrasonic water wash | 9 June, 2009

We are using a water soluble flux which requires the assemblies to be cleaned in an ultra sonic cleaner after assembly. Is there a standard that specifies how long the assemblies need to be baked/dried after being submersed in a water solution for a given time?

The JEDEC J-STD-033 defines baking condidtions prior to board mounting. I do not think this standard applies to finished assemblies after they are washed. Is that a correct assumption? What guidelines do you use in this situation?

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#59050

Baking assemblies after ultrasonic water wash | 10 June, 2009

You're correct that JEDEC J-STD-033 defines baking condidtions for moisture sensitive components.

Why do you want to bake assemblies after cleaning?

Search the fine SMTnet Archives for threads like: http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=57473

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#59053

Baking assemblies after ultrasonic water wash | 11 June, 2009

Our cleaning process involves the assemblies being completely immersed in the water bath of the ultrasonic cleaner. The assembly has a QFP44 on it. Customer stated that when these assemblies have been cleaned with water in the past (at a different manufacturer) they had problems with water being trapped under the QFP. This lead to problems when the board was powered up.

We are in a dry climate wth normal relative humidity levels in the 20-30% range. We allow our assemblies to air dry for 12+ hours after being washed in the ultrasonic cleaner and have seen no moisture problems with this process when the boards are later powered up.

Since the customer has brought up this issue, I am looking at the possibility of going beyond our air dry process. My question is: Is our air dry process sufficient or do I need to bake the assemblies to ensure there is no water trapped under the QFP? If a bake is recommended, what temperature and length of time should I use?

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#59055

Baking assemblies after ultrasonic water wash | 11 June, 2009

NASA recommends baking a PCB for a minimum of 4 hours at 93+/- 5.5�C before conformally coating. [NASA-STD-8739.1, �Workmanship Standard for Staking and Conformal Coating of Printed Wiring Boards and Electronic Assemblies,� August 6, 1999]

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#59114

Baking assemblies after ultrasonic water wash | 24 June, 2009

Try immersing the assembly in IPA for 30 minutes. IPA is hydroscopic ans will drive off most of the water. Dry the assembly. Then bake at 110°C for 2 hours.

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#59129

Baking assemblies after ultrasonic water wash | 25 June, 2009

Shanelo Technologies

Given that isopropyl alcohol [IPA] is produced by combining water and propene. How does soaking a board in water and a flammable liquid drive off water?

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#59132

Baking assemblies after ultrasonic water wash | 26 June, 2009

IPA is hydroscopic.

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#59156

Baking assemblies after ultrasonic water wash | 30 June, 2009

He wants to "see underwater"

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kpm

#59160

Baking assemblies after ultrasonic water wash | 1 July, 2009

But the boards and parts on the boards are also hygroscopic(no not a typo I did a search on hydroscopic and it is not a word the actual word is hygroscopic look it up if you don't believe me) so if you have two hygroscopic materials which one wins?

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