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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Popcorn effect with PBGA

emmanuel

#4513

Popcorn effect with PBGA | 4 April, 2000

In some technical reports, i have recently read that when processing a PBGA, it is worth controlling the reflow temperature under 205�C. Indeed, over 205�C some people have noticed plenty of popcorn effects.

Is this point really true ? Does this temperature limit really exist ?

Any hints about this topic will be welcome.

Emmanuel

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#4514

Re: Popcorn effect with PBGA | 5 April, 2000

Emmanuel: Popcorn effect is mostly caused by entrapped moisture in the components package material. Plastic ICs are known for absorbing and storing moisture when exposed to normal factory conditions. They should be stored in an moisture reduced environment (Sealed Drybags or humidity controlled cabinets). IPC-SM-786A says for example in the case of rework where the possibility of moisture saturation is given you should not exceed 200�C for those components or first prebake the unit. If proper handled those components should withstand normal reflow conditions without harm. Could be that people noticed this popcorn effect without adequate handling procedures prior to soldering. I would always look what reflow temperatures are recommended by the manufacturer.

M2C

Wolfgang

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Kal C.

#4515

Re: Popcorn effect with PBGA | 5 April, 2000

Hi Emmanuel,

There is lots of info. in SMTNet archive (I think 98 Sept-Dec). I had a lot of problem with PBGA and certain uBGA with their PCB base material (FR-X) and encapsulant. Wolfgang is correct. We had to reprofile our reflow oven , qualify and characterize SMT top/ bottom/ BGA replacement process. We also had to get some extra nitro-cab. close by the repair station. You can minimize popcorn effect under limit but can never get rid of it with PBGA type.

If you dont mind me asking,what kind of failure modes are you experiencing for popcorn effect? How is your thermal mass distribution on entire assembly during reflow.

Let me know.

Hope it helps.

Regards Kc.

Regards Kc.

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emmanuel

#4516

Re: Popcorn effect with PBGA | 11 April, 2000

Hi Kc,

As recommended by the PBGA supplier, the temperature of the package surface should not exceed 225�C during 10 seconds max so as to avoid popcorn effect.

Given that some of products reflow profils are specifiing reflow temperature at 250�C, i expect to see delamination between the die pad and the mold compound, between die pad and die atttach.

Let me know if according to your experience, the specified temperature (225�C) is so critical or not ?

Thank you for your help,

Emmanuel

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