OKUNO offers a wide range of surface treatment chemicals for the manufacturing process of printed wiring boards that are essential for electronic devices and home appliances. Explaining the typical manufacturing process of multilayer PWBs, and we introduce our product line-up to support your manufacturing processes.
CCL (Copper Clad Laminate) is used as a substrate. Conduct board sizing and tooling-hole drilling. The tooling holes are used to align top-side and bottom-side circuits as well as inner and outer copper layers in a right position.
Prepare a next step, DFR (Dry Film Resist) lamination. To increase DFR adhesion, etch the surface of copper foils by jet-scrubber, buff brushing.
Laminate DFR on copper foils. DFR is used as a photosensitive material for photolithography.
Apply masks (films, metals or glass) partly on DFR and expose light onto the whole surface. Currently, LDI (Laser Direct Imaging), which doesn’t require mask application, is increasing.
Dissolve the mask-applied (unexposed) areas with sodium carbonate solution. The masks remaining on copper foils is used as a resist for a next etching step.
Etch copper foils with copper (II) chloride solution or an etching solution, and form circuit patterns.
Strip DFR with an alkaline solution. Stripping bathes foam by using, so anti-foaming agents are generally used.
Etch the surface of copper foils to ensure adhesion of copper foils and pre-preg (partially cured resin composite) in multi-layer fabrication process. Generally, oxidize the surface of copper foils to obtain a roughened surface. The surface of copper foils change black after this treatment, so this step is called a black oxide treatment.
Laminate pre-preg and a copper foil on the both sides.
Heat the laminated layers under a pressure of several tens to one thousand ton in a vacuum Melt pre-preg by heat to multi-layer PWB formation.
Drill PWBs to make through holes.
After the drilling step above, melted and decomposed resin components still remain onto the inner copper layers in the through hole. De-smear is conducted to remove these residues from the hole and to increase connection reliability. Also, the inside wall of the hole is etched in this process to enhance the adhesion of electroless copper plating and copper electroplating.
In copper electroplating, the plating is conducted into through holes to ensure the electric conductivity between top-side and bottom-side circuits and between inner and outer copper layers. Electroless copper plating plays a role as the first layer before the copper electroplating. Before the electroless plating, cleaning, hydrophilization, catalyzing and accelerating steps are necessary as pre-treatment steps.
Increase the thickness of the plated film in the through holes by electroplating. In this process, it is important to increase the thickness of the film not only in through hole but also on the surface area of printed wiring boards in order to ensure pattern formation performance in the later etching step. Thus, high throwing power is strongly demanded to copper electroplating (acid copper plating) solutions.
Prepare a next step, DFR lamination. To increase DFR adhesion, etch the surface of copper foils by jet-scrubber, buff brushing.
Laminate DFR on copper foils. DFR is used as a photosensitive material for photolithography.
Apply masks (films, metals or glass) partly on DFR and expose light onto the whole surface of copper foils. Currently, LDI (Laser Direct Imaging), which doesn’t require mask application, is increasing.
Dissolve the mask-applied (unexposed) areas with sodium carbonate solution. The masks remaining on copper foils is used as a resist for a next etching step.
Etch copper foils with copper (II) chloride solution or an etching solution, and form circuit patterns.
Strip DFR with an alkaline solution. Stripping bathes foam by using, so anti-foaming agents are generally used.
Apply PSR (Photo Solder Resist) on the through hole by screen printing or static printing. Film-type solder resist can be also used. Film-type solder resist is applied in a vacuum laminating machine.
Apply masks around the through hole, and expose light onto the whole surface.
Dissolve the solder-resist applied (unexposed) areas with an alkaline solution.
Electroless nickel/(palladium)/gold plating, electroless tin plating, solder leveling treatment (solder melting plating) are conducted for surface mounting. Before the electroless nickel plating, cleaning, catalyzing and post-dipping steps are necessary.
