PCB Manufacturing

How to Choose the Appropriate Via Hole Filling Types for Your PCB?

Via Hole Filling

What is Via Hole Filling?

A via hole filled with epoxy material or other materials is called Via Hole Filling. The via hole filling materials may be Conductive or nonconductive. This technique is used to avoid liquid or air bubbles inside the via hole which helps the assembly process. It also helps to improve the signal integrity, reliability and heat management.

The Benefits of Via Hole Filling

  • Via hole filling allows via in pad technology
  • Micro via in pad
  • Through hole via in pad
  • Via hole filling creates more space for components on the surface of the PCB
  • Via hole filling provides more design options for improved signal performance

Introduction of Via Filling Types

Via Filling Types

Via filing types always depend on the specific application and technology of PCB. Via hole filling materials generally used are copper fill, conductive epoxy and non-conductive epoxy. The most common via hole filling method used to fill the vias is nonconductive epoxy.

Via Tenting

Via tenting is one of the via hole filling methods to cover the vias with solder resist. The designer ensures to remove the solder mask openings which are for via holes. This via hole filling method helps the designer to avoid the short due to the via annular ring in copper. This is the standard via hole filling method for via fill without adding extra cost which the designer can set itself. Today the LPI solder mask layer thickness is very thin so it cannot be held on larger via holes. So the via hole size should be less than 0.3mm to cover via by solder resist and to get the better result.

This via hole filling method is not recommended as this via hole filling method only covers the vias by solder resist and does not fill the vias 100 %. This does not work for via in pad technology.

Copper Via fill

Vias are filled with copper (copper filled via). Copper filled via is one of the common filled vias methods used in the PCB assembly. This can be standard vias or Blind/buried vias. Whenever designers have to design a high-power electricity board, to increase thermal conductivity and electrical conductivity copper via fill method is used. By filling the holes with copper, heat is transferred from one side of the board to the other, reducing the heat on one side of the board, thereby reducing board defects and increasing the life of the PCB.

  • Min via size – 0.0039”
  • Max via size – 0.010”
  • Do allow for increased copper on the surface due to via plating.
  • Via may be mechanically drilled or laser drilled.

Conductive Via fill

Whenever a large amount of heat transfer is required in PCB this via hole filling method is preferred. Material may be copper or silver epoxy. For example, whenever there is Microprocessor ICs are required in the board, then the conductive via method is used to transfer the heat to pass another side also called the heat sink. This via hole filling method is used in high-temperature PCBs to achieve higher thermal conductivity. This is more expensive as compared to the non-conductive via hole filling method.

Non-Conductive Via fill

This is the most common and popular via hole filling method used for via filling. The non-conductive paste is used to enter the vias and fill it completely. It provides better stability and reliability. You can cover the via annular ring and plug the via hole.

In via in pad case, this will result lower in the assembly process. When assembling components, the solder paste does not adhere and points downwards, which can result in weak solder joints.

In the case of Via in pad, the designer can choose the VIPPO method which is very popular today in PCB technology. VIPPO offers via in pad plated over (Plugged and Capped). The epoxy filled vias are another common filled vias method in the PCB assembly. These mean that the via is filled with epoxy (epoxy filled vias) and then the surface of the via is smoothed with copper to get the best results when soldering the components.

The nonconductive via hole filling method is cheaper than the conductive via hole filling method.

LPI Via Fill

In this via hole filling method, via is filled with solder mask material, which is called LPI plugging. This is the low-cost via hole filling method due to no more extra processes required in this method. But this via hole filling method is not suitable for advanced circuit boards like via in SMD pads or BGA pitch.

Via Fill Materials

  • Should be 100 % Solid, but easy to process (no solvents)
  • Should be easy to plate on top with good plating adhesion
Conductive via fillNon-conductive
Tatsua AE3030Taiyo THP-100 DX1
CB100Peter PP2795
Sanei PHP 900 IR 10F

 

How to Choose the Appropriate Via Filling Type

Every via filling type has different functions, so generally speaking, we choose the via filing types and technologies according to the functions and PCB techniques. For example, we use LPI via filling for normal PTH vias,  we use con-conductive via fill for buried vias, and we use con-ductive via fill for VIPPO design. Here are a few factors we need to consider in choosing via filling types.

Via Fill Process

Via fill process requires an extra plating process. First of all, the only via fill hole is drilled through the PCB and then it is plated through the plating process. After that, this hole is filled through the button plate process by creating special via fill layers.

When filling vias, it should be taken care of to avoid the dimples or bubbles on via fill pad.

Design Guidelines

For Conductive or Non-conductive Via fill Min. The hole size should be 0.010” and the maximum hole size should be 0.030”.

The hole should be smaller than the panel thickness. This ensures the via fill material will hold within the hole without sagging or running out.

In High-Speed Technology Boards today, Via Fill is used in Via in pad technology.

Structures of Via in Pad

In Via in Pad design, via pads are directly connected to the legs of the SMD components. These vias are connected top to bottom and inner layers of the PCB.

The Via in Pad method is more reliable instead of using a separate Via pad connection to connect SMD pads. Seeing the below image, vias are drilled in the SMD pads and it is then plated, filled and capped. Via in Pad is typically a long process that requires special Machinery. Via in Pad is best to use in HDI boards, for Via in Pad reduces the space requirement and simplify the thermal management.

Via In Pad is suitable in case,

  • To improve the thermal performance.
  • To Increase density
  • To Improve Electrical Performance
  • High frequency application
Transformation of QFP configuration to Via-in-Pad

Transformation of QFP configuration to Via-in-Pad

Via in SMT/SMD pad Example One

Via in SMT_SMD pad Example One

Via in SMT/SMD pad Example Two

Via in Pad is now commonly used in HDI PCB technologies like micro vias, blind vias, and buried vias using via in pad technology.

Via in SMT_SMD pad Example Two

Via in BGA Example One

Via in BGA Example One

Via in BGA Example Two

Via in BGA Example Two

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