PCB via plugging Technology
Most of PCB manufacturers use Al sheet to plug vias.We use blank net to make solder mask and plug vias after many experiences, it’s stability and reliability.
As the development of electronics industry, customers put high requirements for PCB surface mounted technology.Via plugging come into being as it connected all circuits,then it must meet below requirement :
(1.) Vias can plugged or not plugged,just ensure it plated in vias wall.
(2.) It must have tin/Pn in vias with thickness 4um, no solder mask inflow into vias lead to tin bead plugging.
(3.) Use solder mask ink to plug vias,no light through vias,no tin ring,no tin bead and surface must be flattening.
There are many of high density and BGA boards required via plugging as the electronics products became smaller,lighter,thinner. 4 factors why customer required via plugging.
- Avoid circuits short as tin bead runing around when PCB solder wave process,especially vias in BGA Pad.
- Avoid solder flux remain in vias.
- Avoid surface solder paste inflow into hole lead to cold solder.
- Avoid solder beading run out when solder wave, lead to short circuit.
For surface mounted technology,especially BGA and IC package required surface must be flattening,concavo-convex tolerance +/-1mil,no solder beading.For meet customer requirement, there have many methods to plug vias,the technology time is complex and the hard to control.always happened solder mask peeling after solder wave.
- Plugging vias after HASL
The process is: solder mask printing—> HASL—>Pluging—>Solidified . Use non-plugging process to make, use Aluminum sheet or silkscreen to fill the vias after solder wave. the solder mask oil can be liquefied or UV oil just keep the color is in uniformity. this technology can guarantee solder mask no peeling after solder wave.but it will pollute the surface of board. it will lead to cold solder when SMT. many customer don’t accept this method.
- Plugging vias before HASL
2.1 Use aluminum sheet plugging,solidified,curing and image transfer
This process use NC drill for aluminum sheet and make it to silkscreen and plugging,ensure plugging via plump,solder mask oil can be liquefied or UV oil, the advantage is strong hardness, small resin shrink,good sticky with via wall. the process is : Pre-treatment—>plugging—>curing—>image transfer—> etching—> solder mask printing.
Use this method can guarantee vias be plugged with flattening and no erupt oil,edge of holes oil peeling,but this technology required one time plating copper, make hole wall thickness achieve standard of customer. it must be well plating of whole panel,and must have high capability of curing equipment,guarantee complex remove the remain resin on copper and no smear.
2.2 Solder mask printing after aluminum sheet plugging
This technology use NC drilling to make aluminum sheet and make it to silkscreen. use 36T silkscreen make solder mask after plugging,the time is less 30 minutes, the process is : Pre-treatment—> Plugging—>Silkscreen—> Pre-bake—>Exposure—>Development—>Solidified.
Use this method can guarantee via plugged flattening and well covered and solder mask color uniformity. it can ensure no inflow tin to hole and no solder beading after solder wave.
2.3 Aluminum sheet plugging,development,pre-solidified.curing,solder mask printing
NC drilling for aluminum sheet and make it to silkscreen and plugging.plugging must be plump and solidified. the process is : Pre-treatmemt—>plugging—>Pre-baking—>development—>Pre-solidified—>solder mask printing.
As this method can ensure no oil peeling and blast oil, but it will risk tin beading in hole.so many customers don’t accept it.
2．4 Solder mask printing and plugging at the same time
This method use 36T(43T) silkscreen, install at silkscreen machine and use mat board, make solder mask and via plugging as the same time, the process is : Pre-treatment—>Silkscreen—>Pre-baking—>Exposure—>Development—>Solidified.
This technology use less time and high efficiency,and can guarantee no oil peeling after solder wave and no tin on hole, but as use silkscreen to plugging, there will have much more air,when solidified,air expand,rush and break solder mask film, lead to void,and no flattening.