SMT, PCB Electronics Industry News

Resin plug application and process

May 16, 2019

With the development of miniaturization of assembly components, the layout area and pattern design area of PCBs have also been continuously reduced, and PCB manufacturers are constantly updating the production process to conform to the development trend. The application of the resin plugging process has also become more and more extensive, and it has been used in HDI panels.

1, The application of resin plug:

At present, the technology of resin plug is mainly used in the following products:

1.1, Resin plug for POFV technology.

Directly drilling on the PAD connect to the other layer trace by via, and then fill the via hole with resin and copper plated onto the PAD, this structure is called VIP hole (Via in pad), and the manufacturing process is called POFV (plated on filled Via).

Technique theory
Plug the hole with resin, then copper plated on the surface.
  As illustrated in the following figure:

 


Advantages of POFV technology

1. Reduce the hole-to-hole spacing and reduce the area of the board.

2. Solve the problem of wires and layout and increase the wiring density.

 

1.2, Inner layer HDI resin plug hole

a, Technology theory

Plug the inner layer buried hole with resin, then pressing. This process balances the contradiction between the controlling of the dielectric thickness and pp filling requirement for the inner layer buried holes.
a.1. If the inner buried hole is not plugged completely with resin, the board will explode when it is overheated and directly scrapped;
a.2. If not use resin plug, multiple Prepreg are needed for pressing to meet the requirements of the glue filling. As a result, the dielectric thickness between layers may be too thick due to the increase of the PP sheet.
 

b, Application for inner layer HDI board resin plug

b.1. Inner layer HDI resin plug holes are widely used in HDI products to meet the design requirements of thin dielectric layer requirements.

b.2. For the HDI product with buried hole design, because the medium combined dielectric thickness design is thin, it is often necessary to add the inner layer HDI resin plug process.

b.3. Partial blind hole products because the blind hole dielectric thickness is greater than 0.5mm, the glue can not fill the blind hole completely when in pressing process, then need to plug the blind holes completely with resin to avoid occurring the case that there has no copper in the blind holes in the subsequent process.

 

1.3, Though hole plug with resin

In some 3G products, because the thickness of the board reaches 3.2mm or more, in order to improve the reliability of the product, or to improve the reliability of the solder mask plug hole, use resin to plug the through holes within the cost allowed. This is a major product category that has been promoted in the resin plugging process in recent times.
 

2, The process of resin plug

2.1 Production process

The three types of resin plug holes described above have different processes, as follows:

2.1.1 POFV type products (Headpcb group have the following two kind of process)

 
1. Cutting → drilling → PTH / plating → rersin plugging → baking → grinding → PTH / plating → outer layer → anti-welding → surface treatment → molding → electrical testing → FQC → shipping
 
2, cutting → drilling → PTH → I cu → II cu → resin plug → grinding → drilling through hole → PTH → copper plating → outer layer pattern → pattern plating → etching → solder mask → Surface treatment → forming → electrical testing → FQC → shipping
 

2.1.2 Inner layer HDI resin plug type products (Headpcb use two processes: grinding and non-grinding)

 
Grinding process:
1. Cutting material → buried hole inner layer pattern → AOI → pressing → drilling → PTH / plating → resin plug → baking → grinding → inner layer line → browning → pressing → drilling (laser drilling / mechanical drilling Hole)→PTH/electroplating→outer layer→solderproof→surface treatment→forming→electrical measurement→FQC→shipment
 
2, cutting material → buried hole inner layer pattern → AOI → pressing → drilling → PTH → I cu → II cu (thick copper) → resin plug → grinding à inner layer graphics → AOI → press-fit → drill through Hole→PTH→copper palting→Outer pattern→pattern plating→etching→SM→surface treatment→forming→electrical test→FQC→shipment
 
No grinding required process: 
cutting material → buried hole inner layer pattern → AO → pressing → drilling → PTH / plating → inner layer line → browning → resin plug → flattening → baking → pressing → drilling (laser drilling /Mechanical drilling)→PTH/electroplating→outer layer→SM→surface treatment→forming→electrical test→FQC→shipment
 

2.1.3 Through hole resin plug type

a. Cutting→Drilling→PTH/Electroplating→resin plugging→baking→grinding→baking→outer layer→SM→surface treatment→forming→electrical test→FQC→shipping
 
b, cutting → drilling → PTH → I cu → II cu (thick copper) → resin plug → baking → grinding → baking → outer layer pattern → pattern plating → etching → solder mask → surface treatment → molding →Electric test→FQC→shipment
 

2.2 Special places in the process

From the above process, we clearly found that the process is different. Generally speaking, our understanding is that the “resin plug”process is followed by the “PTH and copper plating” process, which we all consider to be POFV products; if the“resin plug”process is followed by the process "Inner Layer pattern", we think it is the inner layer HDI resin plug hole product; if the "resin plug" process followed by the "outer layer pattern" then we consider to be through hole resin plug type;
 
The above different types of products are strictly defined in the process, and cannot go wrong.
 

2.3 Process improvement

A. For products with resin plug holes, in order to improve the quality of the products, people are constantly adjusting the process to simplify his production process and improve the yield of his production;
 
B. Especially for the product of the inner layer HDI plug hole, in order to reduce the scrap rate of the inner layer open circuit after grinding, people adopt the process of plugging hole after the circuit is made, complete the inner layer circuit production first, then pre-curing the resin after the holes are plugged with resin, and then cured at a high temperature in the press-bonding stage.
 
C. At the beginning, for the inner layer HDI plug hole, people use UV pre-curing + thermo curing ink. At present, more often use thermo curing resin, which effectively improves the thermal performance of the plug hole.

Any other technology need to know,please feel free to contact with our R&D department.  E-mail:rd@headpcb.com.

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