PCB resin plug via always has voids problems, it lead to solder area reduce and bring soldering reliability problems.The article analyses the generation factors of voids and how to improve it?
Via in pad technology is used in high frequency design to reduce inductance and increase density, means via plug is the necessary process. The design require the surface nearly flat,as it may cause soldering and reliability problems. Nowdays the process generally plug resin into core board and metallization.Via is filled with resin of printing,curing after using special ceramics and remove excess resin and then slip to pattern plating. Lead to main defects: plugging resin sag,voids,cracks. We can solve plugging resin sag with plug plumpness. Crack caused by its components and general resin solidifying parameters. Voids seriously affect the reliability of production parameters when it happened surface of pad . Voids is also difficult to improve although adjusted the general parameters.Therefore,this paper focuses on analyses and test the factors of voids.find out control method of plug voids.
Plug voids is actually air bubbles in resin, not be overflowed when solidifying. Although Plugged process is normal,but Plug parameters, Screen mesh,Solidifying method,Panel placement method,Plug method,Resin type affect the quality of plugged via.
We will follow the factors to do experiment.
Experiment material：
Manufacture design:
9 units per panel, 0.1mm and 0.2mm via in each units,400 drilling in each via.
Experiment process:
Sheet Cutting—>Brown Oxide —>Lamination—>laser drilling—>NC drilling—>Electroless copper(1)—>PTH(1)—> resin plug—>Solidify—>Ceramic Grinding—>Electroless copper(2)—>Pattern Plating(2)
Confirmation Method:
Use microscope observe section after Ceramic Curing or Pattern Plating
The result of experiment:
1. Different screen mesh and plug parameter
Summary: Screen mesh,plug parameter on the effect of voids is smaller, all has a large number of voids in different place.
2. The result of Solidifying method and Panel placement method
Summary: Solidifying method is no effect for voids,Panel placement method has a certain effect on the voids,but the effect is not obvious.
3. Plug method
Summary: use recycle resin,all the three plug methods have voids. Different result from different plug methods,the quality of plugging: Vacuum plug<Aluminum board plug<Screen printing plug.
4. Plug method and resin type
Summary: use Vacuum plug method, there is no voids for new resin and recycle resin with vacuum removed bubble.
Summary of experiment:
1.Plug parameter,Screen mesh,Solidifying,Panel placement method are very small effective for plug.
2.Use vacuum removed air bubble is great improve for plug voids.
3.Different plug methods lead to different quality of plug.Vacuum plug is the best quality for resin plugging.
4.Use Vacuum plug+new resin or recycle with removed bubble will don’t produce voids.