2019-BTU-web-Vacuum-reflow-Dimock.pdf - 第6页

Why V acuum reflow? “Low void” pastes have shown that void reduction is possibl e, but void levels are still higher than desired. T ypical reflow results in ~ 40% voids in thermal pad s Initially there was hope that the …

• 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.

Why Vacuum reflow?

“Low void” pastes

Michael Meilunas, “Solder Joint Void Analysis: Effects of Paste and Reflow Parameters”

AREA Consortium

Low Void Paste

Hot Profile

Average Cumulative Void %

Standard Paste

Cold Profile - Air

Atmosphere

Paste

Profile

MFL100

Standard NC

Cold 33%

Air Cold 19%

Low Void Hot 13%

very Hot

13%

Cold 18%

Nitrogen Low Void Hot 13%

very Hot

10%