Printed Circuit Boards are at the center of technological advancement in electronics. We use PCBs widely in various electronic devices. Numerous components and connections within these PCBs allow the smooth flow of electrical signals. One such part is the blind via.
This article will take a deep dive into all the important details about PCB blind vias.
What is blind via in PCB
Imagine a drilled hole, into the layers of a Printed Circuit Board. This hole serves as a pathway to connect the multiple layers. An important caveat is that it does not extend through the entire board. They are only visible from one side. Contrary to through-hole vias, these ones penetrate the whole board.
What are the main types of blind via on PCB
There are four main types of blind vias used in PCB designs:
1.Photo-Defined PCB Blind Via: Created using a photolithography process, it is one of the more common types. The PCB substrate is cited with a photoresist— a type of photosensitive material. A photomask is then used to explore the desired via locations. The whole board is then exposed to UV light, which dissolves the unexposed areas, leaving behind the patterned areas of the blind vias.
2.Sequential Lamination PCB Blind Via: This is a stack of individually processed board layers. They are then laminated under high pressure and heat.
3.Controlled Depth PCB Blind Via: These are designed with a specific depth in mind. These vias are created by drilling partially through the PCB substrate to the desired depth and then platting the vias to achieve the required conductivity.
4.Laser Drilled PCB Blind Vias: A laser beam is used to ablate the material and make the via holes in the PCB substrate. This is the blind via of choice in High-Density Interconnect PCBs.
What are the advantages and disadvantages of PCB blind via
Blind vias offer numerous merits and demerits:
1. Space Efficiency: Allows a higher circuit density by connecting different layers. This results in smaller PCB footprints allowing you to build more compact electronic devices.
2. Improved Signal Integrity: By reducing the length of signal paths, blind vias minimize signal degradation and impedance.
3. Cost-Effectiveness: Unlike buried vias, PCB blind via require fewer drilling steps and are less expensive to fabricate.
1. Design Complexity: Specialized design tools and manufacturing processes are required to ensure accurate drilling and alignment of these vias.
2. Limited Layer Count: This limitation should be considered during the design phase to ensure the desired functionality can be achieved.
What are the applications of blind via PCB
PCB blind via finds applications in various electronic devices. Some typical applications include:
1.Consumer Electronics: Smartphones, tablets, laptops, and wearable devices are some of the familiar places where PCB blind via is used.
2.Telecommunications: The telecommunications industry relies on blind vias to achieve high-density interconnects in communication equipment, routers, switches, and network infrastructure devices.
3.Automotive Electronics: PCB Blind via plays a crucial role in automotive electronics. They are used in engine control units, infotainment systems, advanced driver-assistance systems (ADAS), and other electronic components.
4.Medical Devices: Medical devices require miniaturization and high-density circuitry. These vias help optimize space utilization and enhance the functionality and performance of medical devices.
5.Aerospace and Defense: In the aerospace and defense industries, blind vias are used to develop aircraft avionics, satellites, missile systems, and military-grade electronics.
What is the difference between blind via and buried via on PCB
PCB Blind via and buried via are both used to establish connections between layers in printed circuit boards, but there are critical differences between them:
2.Access: Buried vias as a result of their construction have access only to the internal plates of the board, while blind ones have access to more layers.
3.Design Complexity: Integrating blind vias requires more complex design considerations due to the need for accurate drilling and alignment. Buried vias also add complexity, but to a lesser extent since they are confined to the inner layers.
What are the steps of PCB blind via fabrication process
The fabrication process for PCB blind via involves several essential steps:
① Design Phase
You will first determine the location, size, and connectivity requirements of the blind vias during the PCB design phase.
Then, you will use precision drilling equipment to create blind via holes in the PCB substrate. At this stage, you must ensure accurate positioning and dimensions.
You will then apply a layer of copper to the drilled PCB blind via through copper plating.
In some cases, PCB blind via is filled with epoxy or non-conductive materials to enhance their structural integrity.
You can then etch away the exposed areas to define the circuit traces and blind vias.
Laminate the multiple layers of the PCB, including those with blind vias, using heat and pressure.
Apply a PCB solder mask for protection against solder bridges and environmental factors.
Apply a surface finish to the exposed copper surfaces. Common surface finish options include Hot Air Solder Leveling (HASL), Electroless Nickel Immersion Gold (ENIG), and Organic Solderability Preservative (OSP).
What are the hole size of blind and buried vias
The hole size depends on the requirements of the PCB design and manufacturing capabilities. Generally, through-hole vias have a larger hole size than the other two. The radius of PCB blind vias is often set to be 0.1mm and the length to be 0.81mm. This allows you to perform higher routing density in HDI PCBs.
How to plate PCB blind via
Plating blind via is another critical step in the PCB fabrication process to ensure proper electrical conductivity and connectivity. The plating process involves the following steps:
1.Cleaning: Thoroughly clean the drilled blind vias using chemical solutions to remove any contaminants that may affect the plating quality.
2.Activation: Apply an activation solution to the blind vias to promote adhesion between the copper surface and the subsequent plating layers. Activation solutions contain chemicals such as palladium or chloride salt.
3.Electroless Copper Deposition: Submerge the PCB into an electroless copper bath. In this step, a thin layer of copper is deposited on the exposed surfaces, including the walls of the blind vias.
4.Electroplating: After the electroless copper deposition, the PCB is transferred to an electroplating bath. Electrodeposition plates a thicker layer of copper onto the exposed surfaces, further enhancing conductivity and structural integrity.
5.Plating Thickness Control: You can achieve this by monitoring the plating time, current density, and other parameters to ensure uniformity and adherence to specific design requirements.
IPC-6012 surface and hole copper plating requirements
The IPC-6012 standard provides guidelines and requirements for PCBs’ surface and hole copper plating. It specifies criteria for the minimum plating thickness, uniformity, adhesion, and other factors that affect the quality and reliability of the PCB.
The standard outlines different classes or levels of plating requirements, such as:
●Class 1 for general electronic products
●Class 2 for dedicated service electronic products
●Class 3 for high-reliability electronic products.
The plating thickness requirements may vary depending on the class and specific application of the PCB.
As a PCB manufacturer, it is paramount to adhere to the IPC-6012 standard to ensure the quality and reliability of the finished PCBs.
Blind vias within standard PCBs and HDI PCBs layout
They both incorporate blind vias, albeit with different design considerations.
●Standard PCB: Standard boards typically consist of multiple layers with through-hole vias connecting all the layers. However, in specific cases where space constraints exist, or signal integrity is critical, blind vias may be utilized to establish connections between selected layers.
●HDI PCB: HDI PCBs are designed for high-density circuitry. These circuits typically require smaller components and finer trace widths. These boards extensively use blind vias and micro vias to achieve higher routing density and improve signal transmission.
PCB blind vias are the building block of modern electronics. They allow you to achieve compact designs, improved signal integrity, and efficient interlayer connections. Their applications range from consumer electronics to aerospace and medical devices.
Understanding them is essential for PCB designers and engineers to optimize space utilization and enhance the performance of electronic devices.
A PCB blind via is a drilled hole that connects one or more layers of a Printed Circuit Board. An important caveat is that it does not extend through the entire board. Unlike through-hole vias that penetrate the whole board, blind vias are only visible from one side.
● Photo-Defined PCB Blind Vias
● Sequential Lamination PCB Blind Vias
● Controlled Depth PCB Blind Vias
● Laser Drilled PCB Blind Vias
The process of incorporating blind vias in PCB fabrication involves several steps:
4.Filling and Planarization
5.Imaging and Etching
6.Lamination and Pressing
7.Soldermask and Silkscreen Printing