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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Package rebake

Views: 944


Package rebake | 24 October, 2018

Hi everyone, I am new to this SMT. I have just graduated my study, have zero experience in SMT industry as I studied Automotive before.

Ok lets proceed to the main objetive, I have a question regarding package rebake. From what I have learned, the package will go to flux cleaning process after reflow, and straight away will go for prebake before proceeding to the next process, which is underfill. The question is, when the package is not going to underfill within the time allocated (staging time), the package is required to undergo rebake process again, which will be done in the presence of Nitrogen gas. Can anyone explain to me the purpose of this rebake? and why nitrogen gas is used? Anyone can correct me if my understanding is not correct. Thank you in advance.

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Package rebake | 2 November, 2018

are these requirements outlined by your company or the manufacture of the part? if its your company is the product tested? if so the test guys don't usually like to power things up with water trapped in them or under them as it can cause some problems as you could imagine! the other reason may be subsequent process steps like conformal coating/potting etc.. just some thoughts,, dont know the product or your process of course!

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Package rebake | 2 November, 2018

I am assuming that your application is Automotive. The logic here is that the product has got to at least run for 8 years or more. The prebake removes any moisture that may creep into the product during the wait time. A little moisture combined with vibration over extended periods will grow whiskers. This is just chemistry and is well understood. However we have an insane requirement for ROHS to save the environment from Lead the evil in our midst. Even though every car made nowadays is sent to recycling at the end of its useful life. It seems more important to save the environment than to kill the occasional person from say ECU failure after so many years.


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Package rebake | 9 January, 2019

Hi Simond,

The baking process is likely to remove any moisture after the cleaning process. We wouldn't want any moisture trapped as this might cause delamination if the package is subject to subsequent heating/reflow process. Hence there's a staging time controlled here, as the underfill process needs to be completed before the package is absorbing moisture again.

While for the nitrogen gas, during baking, when there's heat and oxygen, it will cause oxidation. Hence with nitrogen in place, there's less oxygen and hence less oxidation form during the process.

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