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

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GCollier

#13299

QFP On both side of a board | 11 December, 1998

Has any body tried reflowing QFP's on both sides of a board.

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Tom

#13300

Re: QFP On both side of a board | 11 December, 1998

| Has any body tried reflowing QFP's on both sides of a board. | GCollier Yes we do that quite often, we are using QFP132 with 0.5mm pitch in pure reflow process for both sides (no glue). It works well, the only problems we have seen was wiht components that where heavy in comparison to the pin/pad surface; like oscilators or big selfs. Those you have to do one the second side as they will fall off if the are on the bottom in the second reflow. Brgds, Tom

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Michael Allen

#13301

Re: QFP On both side of a board | 11 December, 1998

G,

You'll find at least one old thread in this Forum on dual-reflow if you do a search. I found one dated April 7, '98 (searched on "reflow"); this particular thread includes a discussion about the maximum weight-to-surface_area for successful dual reflow (30 g/in^2). In this same thread, somebody stated that SMTA would soon publish a paper on this subject...anybody know if this actually happened?

Also: when applying this 30 g/in^2 rule, it's not clear to me exactly how you need to calculate the surface area. The earlier thread calls it the "surface PAD area", but I imagine that the pad area is less relevant than the lead "foot" area. For example, if a QFP lead "foot" is 0.009" wide x 0.030" long, the foot area is only 0.00027 in^2. Yet the pad area might be 0.012" x 0.080", or 0.00096 in^2, which is 3.5 times the foot area. Can someone clarify this?

I tested a heavy PQFP208 (with integral heat "slug") with a mass of 10g, lead width of 0.009", and foot length of about (?) 0.030", for a Ratio of (about) 178. This part fell off.

| Has any body tried reflowing QFP's on both sides of a board. |

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HallJ

#13302

Re: QFP On both side of a board | 16 December, 1998

| Has any body tried reflowing QFP's on both sides of a board. | This has been done for a long time. The only thing I have seen that could start to cause problems is when you get up to the PQFP208 's that are weighing 10g or more. For this You can place glue under two of the four corners. This is fast and easy and can be done by machine or manually prior to Second pass production.

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