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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Double Reflow



Double Reflow | 21 December, 1999

Currently i am producing a board using dloble reflow process. The bottom side is mostly 0603 chips and some SOIC. The top side is mostly QFP and some heavy component. During the double reflow process , the capacitor chip on the bottom side drop(same type of chip. Is there anything wrong with this particular component or is my profile is wrong? When i try to reduce the temperature on the bottom heater, i face cold solder on the Top side. Pls advise.

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Re: Double Reflow | 21 December, 1999

Hi Edmund,

if it is a 0603 chip there�s obviously something wrong either with your pads or the component itself. We do such things with vapourphase and do not have the possibility of adjusting the profile for bottomside and they still stick to the board. Make sure there is no mechanical cause for that particular chip to be dropped.

Good luck Wolfgang

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Nick Harris


Re: Double Reflow | 21 December, 1999


I agree with Wolfgang there is no reason for 0603s to be falling from the bottom side during the top side reflow. I assume what you are having problems with is a higher mass component like a large tantalum, inductor, or perhaps an active device like a D-pack. 90+% of the SMT assemblies we produce are double reflow. Obviously we try and run the least mass side first to reduce the problem you are having. Sometimes though there are high mass component on both sides. In some cases we apply SMT glue underneath the high mass components on the bottom side that tend to drop off during the second reflow. If you have dispence capability on your line this is an option. If you don't it may still be an option by manually dispencing post solder print, pre placement. Hopefully your reflow is equipped with rails. Rails are pretty much essential when it comes to double reflow.

Best of Luck, Nick

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Justin Medernach


Re: Double Reflow | 28 December, 1999

Edmund, Check your "Air Amp" settings or the equivalent on your oven. Sounds to me like they are probably turned up too high in the reflow zone and you are blowing the components off of the board when the solder goes liquidous.

Regards, Justin

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Mike Naddra


Re: Double Reflow | 28 December, 1999


An 0603 component should not fall from the board durring an inverted reflow pass, provided that:

Your land geometries are correct for the package type (Start with SM 782 guidlines)- as surface tension of the liquidous solder is what holds the component to the board (basically the "retention force" is directly proportional to the surface area of the land and surface area of the component presented to the land, as a function of solder volume)

You have sufficient solder paste volume

You do not have any mechanical forces affecting your process - such as your oven coveyance medium poping or jerking.(This will effectively drop parts off of the inverted pass at reflow temp)


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