Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Wash and bake of blank PCB's before assembly

Igmar

#16790

Wash and bake of blank PCB's before assembly | 12 February, 1998

I would appreciate any information concerning the wash and bake of blank Printed Circuit Boards before assembly. + Is it necessary to wash and bake PCB�s before assembly? + If any, what is the reason for wash and bake of PCB�s? + If any, what type of PCB�s should be wash and baked? + Does wash and bake have any negative effect on the assembly process? Thanks for any help.

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Justin Medernach

#16791

Re: Wash and bake of blank PCB's before assembly | 12 February, 1998

| I would appreciate any information concerning the wash and bake of blank Printed Circuit Boards | before assembly. | + Is it necessary to wash and bake PCB�s before assembly? | + If any, what is the reason for wash and bake of PCB�s? | + If any, what type of PCB�s should be wash and baked? | + Does wash and bake have any negative effect on the assembly process? | Thanks for any help. Igmar, You don't want to wash and bake PCBs prior to assembly. The most predominant impurity found on boards in storage is SN/PB oxidation. Surface mount pads will oxidize if exposed to the ambient for a long enough period of time. Washing boards will not remove this oxidation. The baking process is for removing moisture. It also introduces new oxidation and acts as a catalyst on existing oxidation. Washing the boards will remove oils and dirt, things that should not get on PWBs in storage in the first place. Some facilities bake all boards as a part of their normal production process. I feel as though this is a wasted step. SCI sets thier process such that boards have to be processed within a short time after removal from a baking oven. There is good reason for this. Any moisture that a PCB picks up will be picked up within 24 hours of baking the board. You can check this yourself if you have a very accurate scale. Bake a board and weigh it immedeately after it is cool. (If it's still warm, the warm air convection from the board will give an errant reading on the scale) Wait 24 hours and weigh the board again. You will see the weight of the water that the PWB picks up over night. The bottom line is that the only time you want to wash and bake boards prior to processing is when you get a physical contaminant on the board or if they have been sitting in an ambient environment for an extended period of time.(a year) Good luck and best regards, justin medernach

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test

#16792

test | 22 April, 1998

test

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#16793

Re: Wash and bake of blank PCB's before assembly | 16 October, 1999

I have just completed a study of the physics involved in drying. If you would like a copy send a request to me

Stu Leech sleech@ix.netcom.com

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