Via in PAD(VIP) PCB

In PCB design,via in pad (VIP) technology is widely used in small size PCBs with limits space for BGA. the via in pad process allows vias to be plated and hidden beneath BGA pads. it required PCB manufacturer plugged the vias with epoxy and then plated copper over it,made it virtually invisible.

Advantages with via in pad technology are:

•  Via in Pad can improved trace routing.
•  Via in PAD can help thermal dissipate.
•  Via in pad can help reduce inductance in high frequency board.
•  via in pad can provide a flat surface for component.

However, there are some disadvantage:

•  The price is high compare normal PCB as complexity manufacturing process.
•  Risk solder off of the BGA pad if you get low quality .

Via in pad Technical Principle

Plug the hole in the inner layer with resin and then press it together. This technique balances the contradiction between the thickness control of the bonded dielectric layer and the design of the inner hole filling design.

•  If the inner hole is not filled with resin, the board will explode when the heat shock occurs, and the scrap will be scrapped directly;
• If you do not use resin plugging, then need multi-sheets PP pressing to meet adhesive demand, but this way, the thickness of the dielectric layer between the layers will increase because of PP caused too thick.

The application of via in pad

• The via in pad plugging resin widely used in HDI products to meet the design requirements of thin dielectric layer.
• For the design of buried and blind holes in inner layer, often also need to increase the inner resin filling process because the middle medium design combined partial thin.
• Some products because the thickness of the blind hole is larger than 0.5mm, unable pressing adhesive to fill the hole, also need resin plugging to fill the vias avoid blind hole without copper problems.

Produce process

Laminate Shear—>Drilling—>P.T.H.—>Panel Plating—>Resin Plugging—>Polishing—> PTH Drilling>P.T.H.—> Panel Plating—>Outer Layer Image—>Pattern Plating—>Etching—>S/M coating—>Surface Finishing—>Routing—>Test—>Backpacking&Shipping

Prevention and improvement measures for the problem of via in pad

• Use the appropriate ink,control the storage conditions and shelf-life of ink.
• Standard inspection procedure to avoid voids in pad holes. Even through excellent technology and good conditions to improve the yield of plugging via, but 1/10000 chance can also lead to scrap, sometimes just because only a void lead to scrap.This can only be done by checking for the location of the void hole and doing repairs. Of course, check the plugging resin hole problem always has been discussed,but there seems to be no good equipment to solve this problem.
• Choice the proper resin, especially the choice of the material Tg and the expansion coefficient, the proper production process and the appropriate removal parameters, can avoid the problem of the separation of the pad from the resin after heating.
• For the problem of delamination between resin and copper, we found that the thickness of the copper on the hole surface is greater than 15um, and the problem of delamination between this resin and copper can be greatly improved.