Experience PCB Perfection with VIPPO: Elevate Your Board Design!
VIPPO stands for Via in Pad Plated Over. As signal speeds, performance requirements and routing densities continue to increase. the use of advanced PCB technology has become increasingly important. And as a result, many of the BGA footprint areas within PCB designs utilized as via-in-pad plated over (VIPPO) structures. or known as Plated Filled Through Vias (POFV) structures. This VIPPO structure is a better pad structure than the more traditional dogbone type. allowing for a wider alignment space between layers, shorter signal path lengths. and reduced capacitance and inductance, two parasitic effects that improve high-speed performance.
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What is VIP(VIA IN PAD)?
VIP stands for “Via in Pad.” It is a technique used in printed circuit board (PCB) design. where a via (a conductive hole) placed directly on a pad of a surface mount component. typically a ball grid array (BGA) or a quad flat no-leads (QFN) package. The purpose of VIPPO is to improve the routing density and reduce the footprint of the PCB.
In traditional PCB design, vias placed outside the component pads. to avoid any interference with soldering or component placement. However, as electronic devices become smaller and more compact. there is a need to maximize space utilization. By placing vias within the component pad. the PCB designer can achieve higher routing density and optimize the use of available space.
Advantages of VIPPO
VIP & VIPPO has some advantages, such as reducing the number of layers required in the PCB. simplifying the routing process, and improving signal integrity by reducing impedance discontinuities. It also helps in achieving better thermal management. by directly connecting the component pad to internal copper planes.
However, there are also some challenges associated with VIP & VIPPO. Placing vias in the pad increases the risk of solder wicking. where solder can flow into the via during the reflow soldering process, leading to potential defects. To mitigate this risk, designers use techniques. such as via filling or via plugging. where the via filled with a non-conductive material. or via tenting, where the via covered with solder mask to prevent solder from flowing in.
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Different Categories of Via in Pad’s
Filled/Plugged Vias:
Vias filled or plugged with a non-conductive material. such as epoxy or solder mask to prevent solder from flowing into the via during the assembly process. This helps to avoid solder wicking issues and ensures reliable solder joints.
Tenting Vias:
In this category, the vias covered with solder mask, which means they are not filled or plugged. The solder mask acts as a protective layer to prevent solder from entering the via. Tenting vias typically used when a non-conductive via filling material is not required. or when cost considerations are important.
Copper-Filled Vias:
These vias filled with conductive material, usually copper. to provide a low-resistance connection between the top and bottom layers of the PCB. Copper-filled vias are commonly used for high-speed signal transmission. or for thermal management purposes.
Stacked Vias:
As we know, Stacked vias are a type of VIP & VIPPO where multiple vias stacked on top of each other. connecting multiple layers of the PCB. So, Stacked vias used when there is a need for routing. between multiple layers while minimizing the space required on the PCB.
Microvias:
Microvias are small-diameter vias used for high-density PCB designs. They are typically less than 150 microns in diameter. and used to route traces between layers in multilayer PCBs. Microvias allow for increased routing density. and are commonly used in modern electronic devices.
These are some of the commonly recognized categories of Via in Pad (VIP) techniques. The choice of which category to use depends on the specific requirements of the PCB design. such as signal integrity, thermal management, routing density, and manufacturing considerations.
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Functions of Via Plugging
Via plugging, also known as via filling, involves filling or plugging the vias with a non-conductive material. to prevent solder from flowing into the via during the assembly process. Here are some functions and benefits of via plugging:
Prevention of Solder Wicking:
One of the main functions of via plugging is to prevent solder from wicking. or flowing into the vias during the soldering process. Solder wicking can lead to unreliable solder joints, shorts, or open circuits. By filling or plugging the vias, the non-conductive material blocks the flow of solder. ensuring that it remains on the component pads and does not enter the via.
Improved Solder Joint Quality:
Via plugging helps to achieve better solder joint quality by minimizing the risk of voids. insufficient solder, or solder bridges. By eliminating the possibility of solder entering the vias. the soldering process can be more controlled. resulting in more consistent and reliable solder joints.
Enhanced Electrical Performance:
Plugging vias can improve the electrical performance of the PCB. By eliminating the presence of conductive material within the vias. the risk of signal interference or impedance variations due to via stubs reduced. This can result in better signal integrity, reduced signal reflections. and improved high-frequency performance.
Thermal Management:
Via plugging can also aid in thermal management within the PCB. By filling the vias with a non-conductive material. heat transfer between different layers of the PCB minimized. This helps to prevent heat from conducted through the vias and enables more effective heat dissipation. through other designated pathways, such as copper planes or thermal vias.
Improved Manufacturing Yield:
Via plugging can contribute to a higher manufacturing yield. by reducing the occurrence of solder-related defects. By ensuring that solder remains on the component pads . and does not enter the vias, the risk of rework or repair. due to soldering issues minimized, resulting in improved overall production efficiency and yield.
It’s important to note that via plugging adds an additional manufacturing step and may incur extra costs. The choice of whether to use via plugging depends on the specific requirements of the PCB design. the level of solder joint reliability needed. and the manufacturing capabilities and processes available.
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Via Plugging Design Experiment
Aspect Ratio:
When using a mechanical drill to create a standard through-hole. it is important to remember that the minimum acceptable drill size. in depends on the thickness of the board. For example, PCB manufacturers require their drill sizes to have an aspect ratio of no more than 10:1. This means that for a 62 mil thick board, the minimum mechanical drill size you should use is 6 mils or 0.006 inches. If you need smaller holes than this, you should consider using microvias with an aspect ratio of 1:1.
Signal Integrity:
Even though the via is short, it is still a measurable length of conductor. which can cause problems with stringent signal integrity requirements. For example, a via connecting the top two layers of a ten-layer board. That would have eight layers of unnecessary metal that could cause interference.
Ring:
The size of the through-hole pads is important. and you need to make sure that you retain a large enough ring after drilling. Mechanical drills can wobble a bit when drilling. and if there are not enough rings, the vias damaged by drill breakage.
Routing Density:
In the case of dense areas of a wiring board, the designer must be careful not to block wiring paths. or ground plane return paths with overvias. This is where the use of blind vias and microvias is critical when planning BGA escapes. so that every pin routed, but important routing paths. and planes are not blocked by the underside of the part.
- Staggered rather than stacked vias chosen because stacked vias require filling and flattening. This process is time-consuming and requires additional expense.
- Implement controlled depths for blind and buried holes.
- Keep the aspect ratio of high-speed vias to a minimum to avoid signal reflection. This provides better electrical performance and signal integrity. low noise and crosstalk, and reduced EMI/RFI.
- Use smaller via holes, especially on HDI boards. to minimize stray capacitance and inductance.
- Through holes in the pads filled unless they exist within the heat sink pads.
- The pad layout where the BGA will mounted can use both blind and through holes. provided they filled and flattened. If they are not flattened, the solder joints compromised.
- Through holes added to the thermal pads underneath the QFNs. to help the solder flow to the conductive planes. These through holes provide a safe solder joint for the thermal pads. and therefore stop the solder from floating the package during assembly. This can affect the quality of the solder joint for QFN contacts.
- Assembly shops can compensate for the lack of through-holes in the thermal pads. by adding a window-glass shaped opening in the solder paste stencil above the pads. which mitigates solder buildup and outgassing.
- Check alignment and via holes for minimum clearance from wiring/indentation edges.
- Check the location of the vias in the case of BGA packages.
- In the design, each via hole separated from