PCB Manufacturing

The Comprehensive Guide to VIPPO (Via-in-Pad Plated Over Filled Vias)

VIPPO via in pad

Vias play a critical role in designing PCBs, they are tiny holes lined with copper which provide interconnectivity between the components through different layers on a multi-layer board. They can be a PCB design engineer’s best friend i.e. they help in reducing the size or achieving Miniaturization of the PCB. Miniaturization is a key aspect of today’s technological innovations as we are constantly packing more components into smaller enclosures, specifically in products like smartphones, tablets, wearables, medical devices, and automotive components.

This means PCB manufacturers must constantly innovate by bringing in new technologies or updating older tech to help reduce the size of the PCBs. With increasing component density,  VIPPO (Via-in-Pad Plated Over Filled Vias) is a very complex but excellent technology for fitting all your components on a compact PCB.

What is  VIPPO (Via-in-Pad Plated Over Filled Vias)?

The full name of VIPPO is Via-in-Pad Plated Over Filled Vias, also called resin plug hole. It is a PCB manufacturing technology that uses electroplating filling technology on via in pad.

By placing vias directly underneath your components, we can decrease the fanout length, while also decreasing inductance and resistance in power delivery components and improving signal integrity for high-speed circuits. In the past, PCB designers mainly used this technology in fine pitch BGA to decrease fanout length. But since now with increasing component densities, they are used on all components and directly lead to space savings on a PCB which can be utilized to either place more components or for routing channels and impedance matching.

The caveat to using via-in-pad technology is that if we mount components on traditional via holes, they will lead to bad solder joints due to solder wicking into via holes. So vias need to be filled and planarized to create a flat surface and to ensure solder remains on the pad for proper attachment with the component.

VIPPO: Type VII filled via according to IPC 4761

What is a filled via?  When via holes are filled with conductive or non-conductive material they are called filled vias. The technology of filling vias has been around since the late 1980s to early 1990s, and with the advent of advanced manufacturing techniques like laser drilling and via-in-pad technology, filled vias have become even more predominant.

As per IPC 4761, there are 7 different classifications of the methods to achieve filled vias and each has its advantages and disadvantages. But for via-in-pad technology w.r.t optimal component mounting, the recommended method is – Type VII according to IPC 4761 – vias filled on the entire cross-section with a dielectric material and then covered with copper (Copper plated over the top of filled holes). It is also known as Vippo – via in pad and plated over or POFV – plated over for vias, they are similar terms and can be used interchangeably.

Vippo tech

Benefits of Vippo/ POFV

  • Suitable for HDI PCB: VIPPO is particularly useful in HDI PCB which uses fine pitch BGA (pitch ≤ 0.65mm) where VIA placement must be precise. This will contribute to not only area reduction but also the number of layers as designers have access to more routing channels. It is also common to see designs with BGA’s with large pin counts utilizing VIPPO and non-VIPPO vias on the same package to achieve better space utilization, with improved electrical, thermal, and mechanical performance.
  • Enhance Component Stability: Another benefit is that the planar surface created by VIPPO will lead to reliable component mounting and soldering. Filled Vias also provide better overall structural integrity than non-filled vias as it helps in reducing mechanical stress and warpage.
  • High Heat Dissipation, Signal Integrity and Power Delivery: They also provide better heat dissipation as the copper plating over the filled vias helps in providing a path so that heat is evenly distributed across the PCB. It was also mentioned earlier in this article about how VIPPO and reduced Fanout lengths directly lead to improved signal integrity and power delivery.

 

Disadvantages of Vippo/ POFV

  • High Cost: Vippo PCB offers significant benefits for PCB miniaturization and performance but there are certain issues that need to be addressed, this includes higher cost which comes with manufacturing complexity and quality control.
  • Difficulty of Filling Large Vias: Also, Vippo PCB is more effective for smaller vias as managing the quality of fill for larger vias becomes challenging.
  • Soldering Challenges: There can be soldering challenges also as, if the filling and planarization are not done properly, it can lead to poor solder joints.
  • Inspection Difficulty: It also affects Inspection, as it becomes more difficult to identify defects. XRAY and AOI tools will be required to identify defects like voids within the dielectric fill or incomplete copper plating.

 

The Basic Process of  VIPPO

The production process involves the steps below:

  1. Drilling hole in the pad 
  2. Plating Copper in holes 
  3. Resin plugging and curing 
  4. Polishing to remove excess material 
  5. Reduce copper thickness to prepare for plating 
  6. Degumming to clean residual contaminants 
  7. Plating vias and VIP surface

Vippo PCB

How to Avoid Issues in VIPPO

While communicating with your FAB house regarding the use of POFV PCB, it is important to provide explicit instructions to avoid potential issues. Here is how to do it:

Explicit Documentation

While communicating with your FAB house regarding POFV PCB usage, it is important to provide explicit instructions to avoid potential issues. The PCB fabrication notes should explicitly call out the drill holes designated for VIPPO tech. This helps avoid confusion and ensures that the fabrication process is followed correctly.

Though most of the ECAD tools have options to specify VIPPO drills, which will reflect in the drill data of Gerber files, it’s good practice to mention VIPPO in the fabrication note as fabrication houses often cross-reference fabrication notes and drill tables.

Ensure drill hole data does not overlap with any press-fit or through-hole components, as this can lead to mounting issues.

Check Manufacturing Capabilities

Please carefully check the manufacturer’s manufacturing capabilities below:

  • Maximum size of via that manufacturer can handle: The VIPPO tech process for large vias becomes challenging, so confirm with the manufacturer on maximum size of the via they can handle. Usually, POFV PCB can become challenging when drill diameter is > 12 mils.
  • Quality Issues: There might also be quality issues such as dimples on the surface of the plated via which can lead to soldering problems at the assembly house. Dimple size should ideally be less than 1 mil to avoid soldering problems at the assembly house.
  • Plugging efficiency: Plugging efficiency is over 75% to minimize the risk of voids which can trap chemicals and contaminants. Larger dimples are acceptable if plugging efficiency is high.
  • Copper Cap Thickness: The copper cap thickness, which is the thickness of Copper plated over the filled via, should be more than 1 mil, with an acceptable range starting from 0.4 mil. Maintaining this thickness can present the SES (Soldermask, Etch, Strip) process.

So verify early in your design process that Fab-houses can meet these requirements.

Large BGA Packages with Mixed VIPPO/ Non-VIPPO Design

Designers can also employ a mix of  VIPPO and non-VIPPO via structures in BGA’s with large pin counts on the same package. In areas of the package where increased routing density is required, VIPPO vias are employed for the signal pins. For ground and power pins where there may be thermal impact due to vias acting as heat sinks (leading to weak solder joints), non-VIPPO or Dog-bone structure vias are used.

 

Conclusion

It is obvious that VIPPO (Via-in-Pad Plated Over Filled Vias) technology plays a crucial role in PCB miniaturization by allowing vias to be placed directly under component pads. Designers must carefully consider the increased manufacturing complexity before leveraging the strengths of VIPPO in their designs to achieve better space utilization, and ultimately achieve Miniaturization.

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