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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Reflow X2

Jonathan Mitchell

#18048

Reflow X2 | 31 October, 2001

Hi All! In the near future we will begin to take on products that require a reflow process on both sides. We will run the backside first (smaller components) to reduce the chances of a part falling off during the second reflow, but my question is about the necessity of using an adhesive on the backside components. Our mother plant has suggested using adhesive in this way but I am concerned about dispensing adhesive directly after printing the solder in fear that the adhesive dispenser will ruin the wet paste. Would someone who is running this process already please take the time to comment on its success or failure? I have also heard that many people use two different types of solder paste for this situation instead; the first paste with a higher liquidus temperature than the second to avoid it becoming liquidus again during the second reflow.

I would greatly appreciate any comments or testimonies to this type of process.

Thank you,

Jonathan Mitchell

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#18054

Reflow X2 | 1 November, 2001

Jonathan,

we do that all day. We do not use different pastes nor do we glue components nor do we run different profiles. Depends on what is meant by "small components". In our case it�s all that "bird seed" up to SO8. That will work for more parts. What you can do is just run some samples and you will see what works. Doesn�t take much time and money so. Be sure that no mechanical impact during the second run on the first side is possible. If you use convection reflow check for minimal airflow for the bottom side.

Good luck

Wolfgang

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Dave

#18065

Reflow X2 | 1 November, 2001

Ditto. We run double sided with no special solder or glue with same profile. We place 0806's and soic's. dave

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#18075

Reflow X2 | 1 November, 2001

Wolfgang is correct. Search the fine SMTnet Archives to find information on the component weight versus pad size during adhesiveless double sided reflow. Do not mess with different solder materials.

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#18078

Reflow X2 = Precautions for Moisture-sensitive components | 2 November, 2001

For double-side reflow boards, take note that if you have moisture-sensitive components on the first side, you will need to track their remaining floor life up to the final reflow. This is because the reflow process is too fast to effectively remove any moisture from the components and thus the clock keeps ticking after they are assembled. FOr more information on this topic consult the joint IPC/JEDEC standard, JTD-033, section 8.4.4 (free download at http://www.jedec.org).

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#18123

Reflow X2 | 9 November, 2001

Hi,

I would just like to add, that in our prototype production we often mount doublesided pcb's with components ranging from 0402 to BGA-280 to QFP-100. Of course we also mount and solder the side with the BGA's and QFP's last. Like the others here, we have had no problem with this. We use a vaporphase oven with a liquid that boils at 200 degrees celsius and a standard Sn62Pb35Ag02 solderpaste for dot-dispensing.

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