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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


component baking process

#30547

component baking process | 15 September, 2004

My question is how does heat alone (125DegC for 48hours) diffuse the water vapour in a component, I figure the amount of water vapour in grams per cubic cm will be the same regardless of temp...yes with temp the RH changes but once the component reaches the same temp no diffusion will occur??? I have read many baking procedures and none really mention anything about moisture removal from the baking oven. By my rough calculation there would have the be a RH of less than 1% at 125DegC to create a difference in water vapour pressure. I suppose my thinking here may be flawed but i would like to know why can anyone help please :-)

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pdeuel

#30550

component baking process | 15 September, 2004

RH changes with temprature. That's why your winshield de-fogs when your defroster is on.

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#30600

component baking process | 19 September, 2004

thanks for your reply ....yes the air is then able to hold more water vapour.... but so is the component hence there is no water vapour pressure difference and the component and the air in the oven would still be in equilibrium???? hence no effective transfer... so when the temp is restored the same vol of water vapour will still be inside the component ?? I suspect the oven must have to operate at 0%RH to be effective is this correct???

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blnorman

#30607

component baking process | 20 September, 2004

We require that the ovens used for bake out are vented, thus removing the vapor from the oven.

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#30609

component baking process | 20 September, 2004

The activation energy for diffusion for molded with novolac, biphenyl or multifunctional epoxy mold compounds and air are not equal.

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#30617

component baking process | 21 September, 2004

thanks Dave,

do you know where I can read a little more on this?

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#30618

component baking process | 21 September, 2004

Background on activation energy for diffusion can be found: * Materials textbooks * College lectures posted on the web. Use 'google' or someother search tool.

As a guideline, the higher the activation energy, the harder is is for diffusion to occur.

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