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Reflowing a PowerPak SO-8

Paul O ' Connor


Reflowing a PowerPak SO-8 | 5 November, 2003

When reflowing a Vishay PowerPak SO-8 & using the recommended footprint from the data sheet, the component is skewing in reflow, to solve this we have to add a glue dot to both sides of the part, will making the PCB land pad 1:1 with the Solderable flag of the device eliminate the proble ?

THanks in advance

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Reflowing a PowerPak SO-8 | 5 November, 2003

You might want to try reducing your stencil aperture by 10% first off; if it still swims try using a home plate design. Also if your profile is going into liquidous to fast, this might cause the swimming as well, check your profile.

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Reflowing a PowerPak SO-8 | 6 November, 2003

First, skewing is a perfectly acceptable condition, providing the amount of skewing is not excessive. A-610 provides guidance.

Second, this part is a land grid device. Land grid devices [ie, BCC�, LGA, QFN, MicroLeadFrame�, etc] are essentially BGA devices with the balls removed and with no solder on the pads. Generally, any device that has bare pads under them that attach to corresponding pads on the board qualifies as a land grid.

Third, watch out for LGA with a thermal "slug" under them, like a QFN [and the drains on your MOSFET]. The slug really limits the options if overprinting. If the opening for the thermal slug is too great when using blades (not a pump), the blades can "scoop" paste from the center of the deposit for the slug. Since the pads do not get scooped, the component can end-up sitting higher than the paste deposits under the heat sink. Support the board under the component if the paste opening is larger than about 100-125 thou^2. Print the heat sinks as a grid of apertures that are the size of pads.

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