Analysing the effect of holes in discs and POFV holes

1. the impact of the hole in the disc

Hole-in-disc designs are becoming increasingly common in modern printed circuit board (PCB) manufacturing, especially in modular veneer boards where high assembly densities are sought.This design helps to save space and improve component integration.However, the design of the hole in the disc also brings some potential problems, such as Figure 1-1 (a) shown in Figure 1-1 (a) for the early common form of green oil single-sided plug holes. 

Figure 1-1 Hole in Disc

Risk of cold tearing (shrink tin cracking):

When the soldering discs of BGA corners are designed with holes in the disc (POFV holes), if these holes are not connected to the inner large copper skins (e.g., ground and electrical layers), fusion may occur due to unidirectional solidification of the solder joints and warping of the BGA corners during rapid cooling of the reflow soldering process.This melting phenomenon occurs when the solder joint solidifies and is therefore called cold tearing or shrinking tin cracking, as shown in Figure 1-2.

Fig. 1-2 Mechanism of POFV hole cold tearing (tin-shrinkage crack) formation

Cold tearing can lead to unreliable solder joint connections, which can affect the performance and reliability of the entire board.

Thermal performance effects:

If the hole in the disc is connected with an inner layer of large copper skin, due to the good thermal conductivity of the large copper skin, the heat during the welding process can be more effectively dispersed, thus avoiding the problem of fusion caused by unidirectional solidification. However, the presence of the large copper skin may also lead to increased thermal stress during the welding process, which may have some impact on the reliability of the welded joint.

2. the impact of POFV holes

POFV (Plate Over Filled Via) holes, that is, resin plug holes plated to fill the holes of the process, also known as VIPPO holes or holes in the disc.The main advantages of this process include facilitating the design of stacked holes and pads on the addition of holes, improve electrical performance, help heat dissipation and can effectively save space.However, the design of POFV holes also needs to pay attention to the impact of the following aspects, as shown in Figure 1-3 for the POFV holes may cause soldering problems schematic.

 Fig. 1-3 Cold Tearing (Tin Shrinkage Fracture) of POFV Hole

Weld Reliability:

Improperly designed POFV holes can lead to cold tearing problems, which can affect the reliability of welded joints.In addition, if the POFV holes are filled unevenly or with defects, this may also lead to problems during the welding process, such as false welds and fake welds.

Electrical Performance:

The quality of filling and plating of POFV holes has a significant impact on electrical performance.Uneven filling or incomplete plating may result in poor electrical connections or signal transmission problems.Therefore, the filling and plating quality of POFV holes need to be strictly controlled during the manufacturing process.

Heat dissipation performance:

Although POFV holes help dissipate heat, they may also be affected by improper design or poor thermal conductivity of the filler material.When selecting filler materials and designing POFV holes, their thermal performance needs to be considered.

In summary, the design of the hole-in-disk and POFV holes has an important impact on the performance and reliability of the printed circuit board.Strict control of the process and quality standards is required during the manufacturing process to ensure that the design of these holes meets the requirements of actual applications and has good reliability and performance.At the same time, designers and manufacturing engineers should pay close attention to the potential problems that these holes may bring, and take appropriate preventive measures to reduce the risk.