Wet characteristics improvement to underfill - Printed Wiring Boards

High density and performance supported by the surface quality improvement technology

Process Objective

Sealing replenishment performance is enhanced by underfills (i.e., liquid hardening resin to protect gold wire of IC chips)


1) Due to poor replenishment and fluidity performance of underfills, wet does not spread over well. Or bleeding out occurs.

2) There is a time dependence on the surface improvement effectiveness

= Difficulty of controlling wettability

Process image

Wet-blast was applied after SR develop and drying process.

  • 1) Cleaning and removal of foreign objects on the SR surface.
  • 2) Improve wettability by expanding the surface area.
  • 3) Bleed prevention by Pinning.

Example of surface quality improvement applied by wet-blasting

Resin solution was dropped on the SR surface, side view observation.

UntreatedWet Blast (A#800)Wet Blast (A#2000)
One Minute After Dropping the Resin SolutionUntreated(Dropping the Resin)Wet blast(A#800)Wet blast(A#2000)
SEM Photograph of the Treated Surface (Angle 10 °)Untreated(SEM)Wet blast(A#800)SEMWet blast(A#2000)SEM
Surface Roughness RMS0.047μm0.237μm0.113μm

↑ Non-directional micro roughness is obtained by wet-blasting.

Differentiation from plasma treatment

1) Polar group independent surface quality improvement

  • As this is the wettability improvement carried by expanding the surface area, its effect does not have time independence.
  • As it does not increase the polarity, the surface does not induce unwanted water.

2) Droplet Pinning Hold


In the case droplet is shrunk

In the case droplet is diffused.

Droplet spreads out due to expansion of the surface area, but micro-roughness at periphery holds it as the function of a dam.


Contact Angle 78.3° (Pure water)

When the surface is flat, the surface tension is working and the droplet shrinks.

After wet-blasting

Contact Angle 79.1° (Pure water)
Water remains wet

The fine uneven surface prevents the droplet movement (shrinks)

Examples of associated equipment
(PFE - Physical Fine Etcher)

Surface treatment equipment for precision physics cleaning to sheet material surfaces like printed-wiring substrates (thickness range: 0.2-2.0mm, width spec: less than 610mm)
It processes both sides of the lamina materials evenly, and is able to continually process automatically the steps from water rinsing to cutwater followed by drying.


  • Wide gun with 630mm in width is used and hence it can process thinner plate with up to 610mm in width.
  • Processing both sides of the work piece is applicable.
  • Continuous automatic processing of blasting, rinse, cutwater and drying is applicable.
  • Processing without damaging the circuit on the surface of substrate is applicable.
  • "Line and space 30um" is applicable.
  • Cleaning for any material types of substrate is applicable.


Work pieceThinner plate materials, Printed Wiring Boards
Work sizeWidth : 610mm and below
Length : 200~700mm
Thickness : 0.2~2.0mm
Conveyor transportation speed0.5~2.5m/min
GunWide Gun 630mm ×2
Power supplyAC200V, 50/60Hz, 3 phases
Power consumptionAbout 15kW (Total rated apparent power of all the equipment)
Air supply pressure0.5MPa or more, 0.7MPa and below
Air consumption19.9m3/min (NTP at 0.25 MPa of preset blast air pressure)
OptionSludge Recovery unit

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