2019-BTU-web-Vacuum-reflow-Dimock.pdf - 第5页

• Voids form for many reasons in cluding: ▫ Paste solvent v olatilization ▫ Paste solids v olatilization ▫ Oxide volatilization ▫ Outgass ing (PCB, Compo nent) V oid formation and growth • Voids grow by merging • Then es…

Voiding is of particular concern for

Thermal management of QFN and other devices

All about keeping the chip cool by eliminating voids in

Thermal Pads because empty spaces don’t transfer heat

Void issues

• Voids form for many reasons including:

▫Paste solvent volatilization

▫Paste solids volatilization

▫Oxide volatilization

▫Outgassing (PCB, Component)

Void formation and growth

• Voids grow by merging

• Then escape the solder if they contact an

exposed surface.

Why Vacuum reflow?

“Low void” pastes have shown that void reduction is possible,

but void levels are still higher than desired.

Typical reflow results in ~ 40% voids in thermal pads

Initially there was hope that the solder paste guys could

find a way to reliably lower or eliminate voids with flux

and thermal profile modifications.