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What is a PCB resin plug hole? Why use a resin plug?

The process of resin plugging has been widely used in the PCB industry in recent years, especially in some products with a high number of layers and large thickness of the board. It is desirable to use resin plug holes to solve a series of problems that cannot be solved by using green oil plug holes or pressure-filled resin. However, because of the characteristics of the resin used in this process, it is necessary to overcome many difficulties in the production to obtain a good quality of the resin plug product.

2, the origin of the resin plug hole:

2.1 Development of electronic chips

With the continuous updating of electronic product technology, the structure and installation of electronic chips are constantly improving and changing. Its development has basically evolved from a component with a plug-in foot to a highly dense integrated circuit module that uses a ball matrix to arrange solder joints. The development history of components can be seen from the following figure:

Earliest CPU

286CPU (plug-in pin)

Pentium series CPU (plug-in foot)

The spherical arrangement of dual-core CPU

Server CPU

2.2 The encounter between two people has made resin plugging technology

In the PCB industry, many process methods have been widely used in the industry, and people have basically not paid much attention to the origin of some process methods. In fact, when the electronic chip arranged in the spherical matrix was just launched, people have been making suggestions for such small chip-mounting components, and it is expected to reduce the size of the finished product from the structure.

In the 1990s, a Japanese company developed a resin that directly plugged the holes and then plated copper on the surface, mainly to solve the problem of air blowing in the green oil plug holes. Intel applied this process to Intel’s electronics to create the so-called POFV (partially called Via on pad) process.

3. Application of resin plug hole:

Currently, the process of resin plugging is mainly used in the following products:

3.1 POFV technology resin plug hole.

3.1.1 Technical principle

A. Plug the via hole with resin and then plate copper on the surface of the hole.

As shown below:

B. Slice example:

3.1.2 Advantages of POFV Technology

l, reduce the hole and hole spacing, reduce the area of the board,

l. Solve the problem of wires and wiring and increase the wiring density.

3.2 Inner layer HDI resin plug hole

3.2.1 Technical principles

The buried hole of the inner layer HDI was plugged with a resin and then pressed. This process balances the contradiction between the control of the thickness of the pressed dielectric layer and the design of the inner layer HDI buried hole.

l. If the buried hole of the inner layer HDI is not filled with resin, the board will explode when it is overheated and directly scrapped;

l If the resin plug hole is not used, multiple PPs are needed for pressing to meet the requirements of the glue filling. As a result, the thickness of the dielectric layer between the layers may be thicker due to the increase of the PP sheet.

3.2.2 example map

3.2.3 Application of inner layer HDI resin plug hole

l, the inner layer of HDI resin plug hole is widely used in HDI products to meet the design requirements of thin dielectric layer requirements of HDI products;

l. For the blind buried hole product with buried hole design for the inner layer HDI, because the intermediate combined medium design is thin, it is often necessary to increase the flow of the inner layer HDI resin plug hole.

l, part of the blind hole product because the thickness of the blind hole layer is greater than 0.5mm, the press-fit glue can not fill the blind hole, also need to carry out the resin plug hole to fill the blind hole, to avoid the hole in the subsequent process, the hole is copper-free problem.

3.3 Through hole resin plug hole

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 green oil plug hole, the resin will be used at the cost. The through hole is plugged. This is a major product category that has been promoted in the resin plugging process in recent times.

4. Process for making resin plug holes:

4.1 Production Process

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

4.1.1 POFV type products (the process of different factories is different)

1. Cutting material à drilling → PTH / plating → plug hole → baking → grinding → PTH / plating → outer layer → anti-welding → surface treatment à forming à electric test à FQCà shipment

2, cutting material à drilling à sinking copper à plate electricity à plate electricity (thick copper) à resin plug hole à grinding à drill through hole à sinking copper à plate electricity à outer layer à graphic plating à etching à resistance welding à Surface treatment à molding à electric measurement à FQCà shipment

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

Grinding process:

1. Cutting material à buried hole inner layer pattern à AOIà pressing à drilling → PTH / plating → plug hole → baking → grinding → inner layer line → browning → pressing → drilling (laser drilling / mechanical drilling) →PTH/Electroplating→Outer circuit àAnti-weld àSurface treatment àFormation àElectrical measurement àFQCà shipment

2, the material à buried hole inner layer graphics à AOIà pressure à drilling à sink copper à plate electricity à plate electricity (thick copper) à resin plug hole à polished à inner layer graphics à AOIà pressure à drill through hole à sink copper à plate electricity à outer layer à graphic plating à etching à resistance welding à surface treatment à forming à electric test à FQCà shipment

No need to grind: open material à buried hole inner layer pattern à AOIà press à drilling → PTH / plating → inner layer line → browning → plug hole → flattening → baking → pressing → drilling (laser drilling/machinery Drilling)→PTH/electroplating→outer line→àresistive welding àsurface treatment àforming àelectric measurement àFQCà shipment

4.1.3 Outer through hole resin plug type

1. Cutting material à drilling → PTH / plating → plug hole → baking → grinding → baking → outer layer line → anti-welding → surface treatment à forming à electric test à FQCà shipment

2, cutting material à drilling à sinking copper à plate electricity à plate electricity (thick copper) à resin plug hole à baking → grinding → baking à outer layer à graphic plating à etching à resistance welding à surface treatment à forming à electric test àFQCà shipment

4.2 Special places in the process

l From the above process, we clearly found that the process is different. Generally speaking, our understanding is that the “resin plug hole” is followed by the “drilling through hole and copper plated electricity” process. We all think it is a POFV product; if the “resin plug hole” is followed by the process “Layer pattern”, we think it is the inner layer HDI resin plug product; if the “resin plug hole” is followed by the “outer pattern”;

l, the above different types of products are strictly defined in the process, can not go wrong; Keding Chemical developed three different inks for the characteristics of the above three processes, TP-2900S\TP-2900\TP-2900C These three inks correspond to the above three processes.

4.3 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 products 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 re-plugging the hole after the circuit is made, first complete the inner layer circuit production, after the resin plug hole The resin is pre-cured and then cured at a high temperature in the press-bonding stage.

C. In the beginning, for the inner layer HDI plug hole, people use UV pre-solid + thermosetting ink. At present, more thermosetting resin is directly used, which effectively improves the inner layer HDI resin. Thermal performance of the plug hole.

4.4 Process method of resin plug hole

4.4.1 Ink used in resin plug hole

A. There are many types of inks currently used in the resin plugging process on the market. Commonly used are the brands of suppliers such as San-Ei and not ti.

4.4.2 Process conditions for resin plug holes

A. There are tens of thousands of holes in the resin plug hole, and it is guaranteed that one hole cannot be full. This one-tenth of the defects will lead to the possibility of scrapping, and it will inevitably require rigorous thinking and regulation in the process.

B. Good plugging equipment is an inevitable requirement. Screen printing machines currently used for resin plug holes can be divided into two major categories, vacuum plugging machines and non-vacuum plugging machines.

Serial number Equipment category Plug hole effect Screen printing machine pressure requirements cost Other influence
1 Vacuum plugging machine it is good N/A high Because it is a whole plate printing, it needs to be equipped with an 8-axis grinding machine. The production of thin plates is easy to cause deformation of the core plate, which increases the difficulty of controlling the expansion and contraction.
2 Non-vacuum plugging machine better ≥7kg/cm2 in

legend:

4.4.3 Plug hole process of ordinary screen printing machine

A. The choice of screen printing machine is important to consider the maximum cylinder pressure, lifting method, smoothness and levelness of the tool holder;

B, silk screen scraper needs to use 2CM thickness, 70-80 degree hardness of the scraper, of course, must have the characteristics of strong acid and alkali resistance;

C, screen printing screen selection can choose either wire mesh or aluminum film; what is to be controlled is to select the appropriate mesh number and the window opening size for the aperture according to the requirements of the plug hole process conditions;

D. The pad used for the resin plug hole has a variety of exquisite, but it is often ignored by engineers. The pad not only acts as a gas guide but also plays a supporting role. For the dense hole area, after the pad is drilled, the whole area is empty. In this position, the pad is bowed or deformed, and the support force to the plate is the worst, which will cause the hole to be inserted at the position. The fullness is very poor. Therefore, when making the pad, to find a way to overcome the problem of large-area vacancies, the best practice at present is to use a 2mm thick pad, only 2/3 of the depth of the pad.

E. In the printing process, the most important thing is to control the pressure and speed of printing. Generally speaking, the larger the aspect ratio, the smaller the aperture, the slower the required speed and the greater the pressure requirement. Controlling slower speeds works best for the improvement of plug holes.

4.4.4 Plug hole process of vacuum resin plugging machine

Due to the high price of vacuum resin plugging machines and the confidentiality of their equipment use and maintenance technology, there are only a handful of PCB manufacturers that can use this technology.

The plugging technology of the VCP vacuum resin plugging machine mainly has an ink clip and two plugs that can be traversed, and there are many small holes in the plug head. After the device has pumped the vacuum, the ink in the ink clip is pushed by the piston to the small hole in the plug hole. The two traversing plug heads first clamp the plate and then fill the ink through many small holes in the plug hole. Through holes or blind holes in the board. The board is hung vertically in the vacuum chamber, and the traversing plug head can be moved down until the hole in the board is filled with resin. The plug head and ink pressure can be adjusted to meet the plug hole fullness. Different board sizes can be used to plug holes with different size plug heads. After the plug hole is completed, it can be scraped off with a doctor blade plug hole and then added to the plug hole ink clip for reuse.

At present, there is also a type of vacuum plugging machine which performs printing by means of a screen and uses a CCD alignment system to align, and its operation is similar to ordinary silk screen printing, but an additional vacuum plug hole flow. This type of plug hole has the best effect, but it has not been widely used due to expensive equipment investment.

The use of a vacuum plug machine is undoubtedly the best way to solve the bubble problem of the resin, and the selection of the plugging ink is basically not limited by the process. However, because the entire surface has a resin, it is very difficult to remove the resin. Need to be used together with a good sander.

4.4.5 Polishing after resin plugging

A. Non-woven cloth grinding machine or belt grinding machine is an indispensable equipment for making resin plug holes. On the one hand, it is required that the equipment should be able to effectively remove the resin on the surface of the board. On the other hand, the roughness of the copper surface is not required. Wipe, scratches and other issues.

5. Common quality problems of resin plug holes and their improvement methods

5.1 For POFV products

5.1.1 Common problems

A orifice bubble

B, the plug hole is not full

C, resin and copper layering

5.1.2 Consequences

A, there is no way to make a pad on the hole; the hole is hidden, the chip is mounted and blown, also called out-gassing

B, no copper in the hole

C, the pad bumps, causing the components or components not to fall off

5.1.3 Preventive measures

A. Select the appropriate plug ink to control the storage conditions and shelf life of the ink.

B. Standard inspection process to avoid the appearance of voids in the hole of the patch. That is, you can rely on the excellent plugging technology and good silk screen conditions to improve the yield of the plug hole, but the probability of one in tenth can also lead to product scrapping, sometimes just because a hole in the hole causes no pad on the hole and is scrapped. unfortunately. This can only be checked to find out where the hole is and to repair it. Of course, the problem of checking the voids in the resin plug has always been discussed, but it seems that there is no good equipment to solve this problem. How to make the accuracy of manual inspection and judgment is higher, there are many different ways.

C. Choosing the right resin, especially the choice of material Tg and expansion coefficient, suitable production process and suitable degumming parameters, can avoid the problem that the pad and the resin are detached after being heated.

D. For the problem of resin and copper delamination, we found that the problem of delamination of such resin and copper can be greatly improved when the thickness of the copper surface of the hole is greater than 15 um. (As shown below)

5.2 inner layer HDI buried hole, blind hole plug hole resin plug hole

5.2.1 Common problems

A bursting board

B, blind hole resin protrusion

C, hole without copper

5.2.2 Consequences

Needless to say, the above problems directly lead to the retirement of the product. The protrusion of the resin often causes the circuit to be uneven and causes an open short circuit problem.

5.2.3 Preventive measures

A. Controlling the fullness of the inner layer HDI plug hole is a necessary condition for preventing the explosion plate; if the plug hole is selected after the line, the time between the plug hole and the press-fit and the cleanness of the board surface should be controlled.

B. The protrusion control of the resin needs to control the grinding and flattening of the resin;

5.3 For plug holes in through holes, the problem is relatively small and will not be discussed here.

6. Promotion of resin plugging technology

With the increasing proficiency in the application of resin plugging technology and the effective solution of stubborn problems like bubbles, resin plugging technology is constantly being promoted. For example, HDI blind holes are used for resin plug hole filling, laminated HDI structure inner layer HDI buried hole VIP process, and the like.

At present, in the industry standard (IPC-650), it seems that the copper thickness on the hole of the resin plug hole has not been given. The potential risk is that once the thickness of the copper plated on the hole of the resin plug hole is thin, after passing through After the surface treatment of the inner layer HDI line, after the browning treatment, the thin copper on the orifice may be drilled by the laser drill hole, and it is impossible to judge the problem during the electric test. But the quality of this thin layer of copper in terms of high-pressure resistance is really worrying.

In this question, according to our experimental data, if the copper thickness above the buried hole is greater than 15um, which meets the requirements of the copper thickness of the Hoz, there is generally no quality abnormality. Of course, if the customer has a higher communication requirement, it is another matter.

in conclusion

After years of development, the technology of resin plugging has been gradually accepted by many users and continues to play an indispensable role in some high-end products. Especially in blind buried holes, HDI, thick copper and other products have been widely used, these products are related to communications, military, aviation, power, network and other industries. As a manufacturer of 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. Good and promote such technologies to achieve the production of PCBs with higher technical difficulty.

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