The process of resin plug hole has been more and more widely used in the rigid-flex PCB industry in recent years, especially in some products with high layers and thick boards. People hope to use resin plug holes to solve a series of problems that cannot be solved by using green oil plug holes or press-fit resin. However, due to the properties of the resin used in this process, many difficulties need to be overcome in manufacturing, in order to obtain good quality of the resin plug hole product.

What is a resin plug hole?

The structure and arrangement of electronic chips are constantly changing and reforming, and circuit board modules have also undergone great changes. The green oil blockage of electronic chips has deeply troubled many smt processors. 1990s, A Japanese company has developed a resin that directly plugs holes and then plated copper on the surface, mainly to solve the problem of green oil plugging holes and blowing air.

Application of resin plug hole

At present, the resin plugging process is mainly used for the following products.

1. Resin plug hole of POFV PCB technology

The vias are plugged with resin and then copper-plated on the surface of the holes. This can not only narrow the hole spacing and reduce the board area, but also solve the problem of wire routing and improve the routing density.

2. Inner HDI PCB resin plug hole

Use resin to plug the buried hole of the inner HDI, and then press it. This process balances the contradiction between the thickness control of the pressed dielectric layer and the design of the inner HDI buried hole filling. This method is widely used in HDI products to meet the design requirements of HDI products with thin dielectric layers.

(1) For blind-buried-hole products with inner-layer HDI buried-hole design, due to the thin design of the intermediate composite medium, it is often necessary to increase the flow rate of the inner-layer HDI resin plug hole.

(2) For some products with blind vias, the thickness of the blind via layer is greater than 0.5mm, and the adhesive cannot fill the blind vias. It is also necessary to fill the blind holes with resin plug holes to avoid punching holes in the subsequent process.

3. Through-hole resin plug hole

In some communication products, because the thickness of the board is more than 3.2mm, in order to improve the reliability of the product, or to improve the reliability problem caused by the green plug hole, the resin is also used to plug the through-hole with the permission of cost. This is a major product category that resin plug technology has been popularized in recent years.

Common quality problems of resin plug holes and their improvement methods

A. Quality Problems with POFV PCB technology

Air bubbles appear in the orifice, the plug hole is not full, and the resin and copper are delaminated. This will result in no way to make pads on the orifice, the hole hides the gas and the chip is out-gassing, there is no copper or pad protrusions in the hole and resulting in failure to attach components or components falling off.

Solution: Control ink storage conditions and shelf life, Check and repair the hole position of the patch port, Select resin with appropriate Tg and expansion coefficient, We found that when the copper thickness on the hole surface is greater than 15um, the problem of resin and copper delamination can be greatly improved.

B. Quality Problems with Inner HDI PCB resin plug hole

It is easy to have problems such as circuit board explosion, blind hole resin protrusion, and no copper in the hole. It will cause the line to be uneven and lead to open and short circuit problems. The final circuit board is directly scrapped.

Solution: Control the plumpness of the inner HDI plug hole or control the time from plug hole to pressing and the cleanliness of the board surface, Controlled sanding and flattening of resin.

C. For the plug hole of the through hole, there are relatively few problems, and no special discussion is made here.

What can we learn?

After years of development, the technology of resin plugging has been gradually accepted by many users and it continues to play an indispensable role in some high-end products. Especially in blind buried holes, HDI, thick copper and other products. These products are related to communications, military, aviation, power, network and other industries. As a manufacturer of rigid-flex PCB products, we understand the process characteristics and application methods of the resin plugging process. We also need to continuously improve the process capability of resin plugging products, improve the quality of products and solve the related process problems of such products. Applying such technologies and promote the production of Rigid flex printed circuit boards to the achievement of higher level technical difficulty.