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SMT electronics assembly manufacturing forum.


Reflowing BGA's 2x on a double sided board

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James

#47955

Reflowing BGA's 2x on a double sided board | 23 February, 2007

I have this board that we are currently having problems with. When we run the BGA side with the hotter temp. the connectors on the other side lift off their pads.

The BGA is lead free, that is why we have to use the hotter profile.

Would it be ok to run the BGA side first with the lead free profile then run the connector side using the lower temp. profile. Would this harm the BGA or would it be ok because it needs a higher temp anyway?

I think this would solve the problem or the other thing I thought about is turning off the bottom heaters. We run on an 8 zone oven.

Any input would be great.

Thanks

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#47956

Reflowing BGA's 2x on a double sided board | 23 February, 2007

Running the BGA first is OK. We run double sided BGA baords all the time without problem.

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Muhammad Haris

#48067

Reflowing BGA's 2x on a double sided board | 1 March, 2007

Hi, I believe ,do the BGA side first and then use glue from dispensor for the connector side.

THIS CONDITION CAN BE FOLLOWED IF & ONLY IF UR CONNECTORS DO NOT BURN OR LOOSE THEIR PHYSICAL STATES. OR SIMPLY REDESIGN THE BOARD KEEPING IN MIND THAT BIGGER COMPONENTS ON ITS ONE SIDE CONTAINING UR CONNECTORS & BGA AND SMALLER ONES ON THE OTHER SIDE OF UR PCB.

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Muhammad Haris

#48068

Reflowing BGA's 2x on a double sided board | 1 March, 2007

Hi, I believe ,do the BGA side first and then use glue from dispensor for the connector side.

THIS CONDITION CAN BE FOLLOWED IF & ONLY IF UR CONNECTORS DO NOT BURN OR LOOSE THEIR PHYSICAL STATES. OR SIMPLY REDESIGN THE BOARD KEEPING IN MIND THAT BIGGER COMPONENTS ON ITS ONE SIDE CONTAINING UR CONNECTORS & BGA AND SMALLER ONES ON THE OTHER SIDE OF UR PCB.

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Wagoner

#48076

Reflowing BGA's 2x on a double sided board | 1 March, 2007

Run the lead free BGA side first. Then run the tin lead side second. We do this on some boards so that we don't overheat the components on the second side. There is no reason that the lead free solder needs to reflow on the second pass.

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#48078

Reflowing BGA's 2x on a double sided board | 1 March, 2007

It sounds like something is a little off here. ROHS compatible and ROHS capable parts are going to be ok with a leaded solder paste and processing unless you are building high reliability product.( some are going to argue that even high rel products are fine) The other way around, using lead-free , "a little hotter profile " with leaded components is not going to be OK. Using two different solder pastes on your product with different processing characteristics is going to introduce variables that would make Failure analysis lots of fun. Joking aside secure your connectors with a dab of SMT adhesive, run that side first and continue with the BGA side after. The suggestion can be tailored some more if you provide more detail.

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james

#48080

Reflowing BGA's 2x on a double sided board | 1 March, 2007

We are using lead paste on both sides, the only reason we need to change the profile is because the BGA is lead free. I decided to run the BGA side first, then the connector side. This way I am not running both sides through on a hotter profile.

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Wayne

#48100

Reflowing BGA's 2x on a double sided board | 1 March, 2007

1) run the BGA side first. set the bottom temp lower (if your reflow oven have top and bottom temp setting) for connector side while doing your 2nd reflow. 2) run the BGA side first with your normal leadfree paste, and run the connector side with low temp leadfree paste (eg. Viromet from Asahi) 3) check with your connector supplier, how high the temp can withstand, and is it ROHS compliance, etc.

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#48109

Reflowing BGA's 2x on a double sided board | 2 March, 2007

There is a formula that determines whether a component will fall off during a 2nd reflow. It takes into account the grams (weight) of the component and the total surface area of the solder joints. I don't know this off the top of my head, but it's in one of my Engineering log books from years ago. Any of you Guru's know this?

Anywho, I vote that you try running the BGA side 2nd. My instincts tell me, with the strength of the BGA joint (and a properly reflowed BGA joint is definitely strong), that your BGA should NOT fall off during a 2nd reflow - even if the 2nd reflow is as hot as the first.

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#48120

Reflowing BGA's 2x on a double sided board | 2 March, 2007

Are you using lead free paste also? Are all the other parts on side 1 ROHOS ? etc.. can they handle your leadfree profile.

Those need answered 1st. But to answer your question. Yes you can run the BGA side 1st ( hopefully with leadfree paste and hopefully by not damaging all your other parts with high temps).

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#48128

Reflowing BGA's 2x on a double sided board | 2 March, 2007

Samir's correct. We've talked about this previously. Search the fine SMTnet Archives for those discussions, like http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=23236

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