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With the increasing integration of electronic products and the smaller and smaller packages of components, vias play a vital role in the interlayer interconnection of printed circuit boards . Therefore, An increasing number of small PCs and BGA (ball grid array) layout designs choose via in pad technology.

With the increasing integration of electronic products and the smaller and smaller packages of components, vias play a vital role in the interlayer interconnection of printed circuit boards . Therefore, An increasing number of small PCs and BGA (ball grid array) layout designs choose via in pad technology.

This article will explore in detail the holes in the plate and the filling process of the holes in the plate in the pcb board.

Table of Contents

What is via in pad in PCB?

Simply understanding, via is a hole on the PCB. A PCB via design is an essential part of the PCB layout design, while via in pad is the hole on the PCB that is pressed on the pad, which plays an important role in the multi-layer PCB layout design.

How many types of via in PCB?

How many types of via in PCB
How many types of via in PCB
  • According to function, PCB via can be divided into two categories:

1. For electrical connection between layers;

2. For fixing or positioning of devices.

  • According to via position in the PCB layer, there are mainly three types:

1. Blind via (blind via): The blind via is on the top or bottom layer of the printed circuit boards,which is used to connect the surface circuit and the inner circuit.

2. Buried via: The buried via cannot be seen with the your naked eye, because it is in the inner layer of the printed circuit boards. The vias should be plated on the internal layers first during PCB assembly, when you choose to use blind via in a multilayer PCB .

3. Via in pad: via in pad, usually referred to as VIP , usually refers to SMD and BGA pads of 0603 and above, and is the best technology for compact electronic and computing equipment today.

4. Micro-via: In PCB design, micro-via is the through hole which is smaller than 150 microns, and it is widely used on HDI PCB.

IPC 6012C-2010 (Qualification and Performance Specifications for Rigid Printed Boards) stipulates the Wrap coating for through via, buried via and blind via, as follows:
IPC6012C minimum requirements for Wrap coating of through via, buried via and blind via
IPC6012C minimum requirements for Wrap coating of through via, buried via and blind via

What are the advantages and disadvantages of via in pad?

Advantages of the via in pad

  • Small space: The space required for via can be minimized , a via in pad requires less space to route signals, so manufacturers can make smaller printed circuit boards.
  • Greatly improve the efficiency of PCB design engineers
  • Via in pad directly connects to layers located below the component for easy routing of signals for HDI PCB design to improve circuit performance.
  • Via in pad need to be filled to provide a flatter surface for components.
    These advantages of via-in-pad make it widely used in small electronic devices , especially in limited BGA spacing and high-speed PCB design.

Disadvantages of via in pad

  • Via in pad filling : For some PCB manufacturers, one of the main disadvantages of via-in-pad is that the pad must be filled with pure copper or covered with copper of some non-conductive material.
  • High cost: Through holes require extra steps, which will increase the time and money cost of PCB fabrication.
  • High requirements: When using a via in pad design, you cannot keep the barrel from filling, and the PCB via in pad needs to be filled when it is placed on the BGA pad.

What are via in pad processes?

What are via in pad processes
What are via in pad processes

Via, located on the BGA pad, is called “via in pad design”. To put it simply, via in pad production process is to plug the resin in the hole, dry resin grinding, and then electroplating copper.
Via in pad process is as follows:

Drilling plate hole → plated copper → plugging resin → curing → grinding → copper reduction → glue removal → drilling other non-plate holes (usually refers to component holes and tool holes) → plated copper and VIP surface copper → other normal processes.

Why need to plug via in pad PCB?

The printed board plug hole program is a production process in the printed board manufacturing process and surface mount technology, and its plug hole function has the following points:

1. Prevent short circuit: the PCB via plug can prevent the short circuit caused by the tin through the element hole during PCB welding or PCB soldering, and caused by fine-pitch devices (such as BGA);

2. Avoid residual flux in PCB via holes;

3. PCB surface mounting and SMT process: printed plate plug hole can prevent surface paste from flowing into the hole, causing virtual welding, and affect the plug hole to keep the pad surface flat, which is conducive to the SMT process.

IPC-A-6012 specifies the coverage requirements, as shown in the figure below:
IPC6012C minimum requirements for Wrap coating of through via, buried via and blind via
IPC6012C minimum requirements for Wrap coating of through via, buried via and blind via

How to fill via in pad PCB?

With the increasing market requirements for light, small and convenient electronic products, PCB is also developing towards the direction of high density, high speed and high frequency, and customers have higher and higher requirements for PCB penetration.

How to fill via in pad PCB
How to fill via in pad PCB

What are types of via in pad plugging?

1. Traditional screen printing method: use a screen printing machine and use special resin to plug holes 2. Special vacuum plugging machine: use vacuum plugging machine and use special resin 3. New vacuum laminating method: use a vacuum laminator and use ordinary PPT The comparison of the characteristics of the three common types of plug hole technology in the plate is as follows:
plugging process comparison
plugging process comparison

What are the different types of via in pad plugging?

The materials for hole plugs in the plate generally include: silver paste and copper paste are commonly used for conductive materials , and resins are commonly used for non-conductive materials.

1. Traditional via in pad plugging process:

Plugging material: ink – permanent resin plugging ink
Plugging equipment: screen printing, special resin plugging scraper, aluminum stencil

2. Vacuum plugging resin plugging process: similar to the traditional screen printing plugging process, the difference is that during the production process of vacuum plugging resin plugging, the product is in a vacuum state, which can reduce air bubbles

3. Vacuum adhesive resin plugging process:
Plug material: thin release material – copper foil, aluminum sheet, release film
Equipment: Vacuum Laminator
Plug hole process: vacuum pressing

Specific process flow (13 steps):
Cutting Drilling → Immersion Copper Hole → Opening Copper Foil/Aluminum Sheet → Drilling, Lamination → Lamination → Cold Tear Adhesive, Grinding → Light Transmission Inspection → Immersion Copper Electrical → Optical Inspection → Section Analysis

Via in pad PCB filling ways

  • Resin plug hole + electroplated copper cap

The hole process of this type of plate is a bit more complicated. First, fill the hole with epoxy resin, and then electroplate copper to seal it. There is no hole in the hole on the surface. It is very smooth, and there will be no tin leakage or soldering problems.

The process is generally used on relatively high-end HDI boards. For example, high-precision devices are used on the board, such as BGA and other devices with multiple pins. The pin spacing is too small to fan out. This kind of hole in the plate has a great advantage, making the wiring smooth. Compared with the ordinary via in pad process, it is relatively complicated, and of course the cost will also increase.

  • Copper paste plug hole + electroplated copper cap

This type of hole-in-disc technology is generally used in positions that require fast heat conduction,such as the GND PAD under the QFN (Quad Flat No-leads Package). The middle of the via hole is filled with copper paste, and then sealed with electric copper.

Since the center of the via hole is filled with copper metal, the thermal conductivity is very good, and it is no different from the resin plug hole from the surface. When the following QFN needs a lot of heat dissipation, this process can be used. After the fabrication is very smooth, the traces of via holes cannot be seen by the naked eye. The heat dissipation performance is particularly good. Of course,the workmanship is very good, but it is more expensive.

Via in pad plugging – Why do Viain pad pcb needs resin plug hole?

Via in pad plugging - Why do Via in pad pcb needs resin plug hole
Via in pad plugging – Why do Via in pad pcb needs resin plug hole

What is the function of the resin plug hole?

  1. Resin filling can avoid surface sinking problems caused by underfilling of lamination flow glue
  2. It can effectively use the three-dimensional space and realize any inter-layer interconnection through hole stacking technology.
  3. Reduce the spacing between holes to solve the problem of wire and wiring.
  4. The contradiction between the thickness control of the balanced press and the design of the inner HDI buried hole.
  5. Improve the electronic performance and reliability of electronic products: shorten the signal transmission wire, reduce the inductive resistance and tolerance resistance of the transmission lines, as well as the internal and external electromagnetic interference.

What is the resin plug process of via in pad PCB?

Resin plug process of Via in pad PCB
Resin plug process of Via in pad PCB

Step 1: Cutting (multi-layer board process after lamination)
Step 2: VIP drilling
Step 3: VIP immersion copper + electroplating
Step 4: VIP resin plug hole
Step 5: Grinding plate
Step 6: Etching thin copper
Step 7: Grinding plate
Step 8: Drilling
Step 9: Immersion copper + electroplating

Conclusion

With the increasing market requirements for light, convenient and small electronic products, high speed PCB and high frequency PCB become more popular, and the requirements of customers are getting higher and higher. Therefore, how to ensure the quality of PCB via and via plugging , and meet the requirements of the market and customers for via in pad PCB ?

IBE always insists on combining the adopted process method with the actual design, and strictly controls the process flow and parameters. Ensure the good operation status of various PCB and PCBA processes, and provide customers with satisfactory products.

FAQ
The via in pad (referred to as VIP) is the hole on the PCB that is pressed on the pad. It is one of the important components of the layout design of the multi-layer PCB. It usually refers to the SMD and BGA pads of 0603 and above. and the best technology for computing devices.

The advantages of via in pad are mainly reflected in the small space and excellent performance
1. Small space: The space required for vias can be minimized, and vias in pads allow manufacturers to make smaller printed circuit boards, which require less space to route signals.
2. The hole in the board is directly connected to the layer below the component, which is convenient for wiring signals, realizes HDI PCB design, and improves circuit performance.
3. The through hole in the pad needs to be filled to provide a flatter surface for the component.

There are two ways of via in pad plugging:

1. Resin plug hole + electroplated copper cap: first fill the hole with epoxy resin, and then electroplate copper to seal the hole. There are no holes on the surface that cannot be seen. It is very smooth and will not cause tin leakage or soldering problems. The process is generally used on relatively high-end HDI PCB.

2. Copper paste plug hole + electroplated copper cap: generally used in positions that require rapid heat conduction, such as the GND PAD under QFN (Quad Flat No-leads Package). The middle of the via hole is filled with copper paste, and then sealed with electric copper. Since the center of the via hole is filled with copper metal, the thermal conductivity is very good.

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