How Do You Use Blind Vias?

A vertical interconnect access (Via) is an important component of a printed circuit board (PCB). The design technology involves a plated through hole in the board for the purpose of routing a trace vertically between two layers. The vias are drilled with a laser or using a mechanical device and then plated so that electrical energy can move between layers.

Blind via are a type of vias drilled in multi layered PCBs. This guide will provide in depth information regarding the design and use of blind vias in PCB.

Blind Vias: An Overview

Blind vias are drilled in PCBs to connect the exterior layer to the interior layer. Manufactures mechanical drill or laser drill blind vias beginning from the top or the bottom of the PCB. The blind vias don’t go through the entire board and can be seen from one of the sides of the board.

The special design of blind vias results in enhanced signal integrity. Moreover, the blind vias design provides greater flexibility regarding more routing options as compared to the through hole design.

The blind vias design results in less space since the hole does not traverse through the board. PCBs with blind vias make more efficient use of the limited space.

What Are the Different Types of Blind Vias?

Blind vias are most used in high density interconnect (HDI) boards. The most common types of blind vias are explained in the following sections.

Laser Drilled Blind Vias

Manufacturers can use an Excimer laser or CO2 laser for drilling blind vias. Laser drilled blind vias are built after the lamination of the board layers. The blind vias are created before coating the surface layer.

A laser is used for removing the copper from the surface layer as well as the insulating substance between the two layers.

Controlled Depth Drilled Blind Vias

Manufacturers create the controlled depth drilled blind vias using the through hole approach with the exception that the hole is drilled halfway through the hole. A pad is placed on the second layer which makes it easy to penetrate the layer.

During the manufacturing of the controlled depth drilled blind vias, manufacturers place components underneath the percolated hole that forms a contact. The percolated hole is then coated with copper while also plating the through hole blind vias with copper.

Photo Defined Blind Via PCB

Photo defined blind via PCB is manufactured by coating the core of the board with a photo reactive resin. The core of the PCB with a photo defined blind via has laminated traces with submerged signal layers and planes.

Before making a hole, the photosensitive sheet is covered with patterns to protect the points where the drills will be made. Moreover, the residues on the board are exposed to wavelength rays to harden them.

Once the holes are drilled, the photo defined blind via PCB is immersed in a solution to remove debris. Afterward, copper plating of the holes and the surface is done to create the surface layer of the board for electrical and thermal connections.

Sequential Lamination Blind Via

Sequential lamination blind VIA PCB involves a unique manufacturing process whereby a thin laminate sheet is passed through multiple processes. The first layer of the blind consists of solid copper material. The second layer is formed by drilling, coating, and sketching the laminate of the board.

During the manufacturing of the sequential layer, the lamination of the subassembly is also done using different layers. The product is finally processed to create a multilayered board.

How Blind Vias Impact the PCB Design?

Blind vias are necessary for PCBs with multiple layers. The vias are necessary to create a high component density in boards with different layers. Moreover, the blind vias also help improve the trace density since the vias can be passed in various directions within the multiple layers. The design of blind vias allows various traces to be connected.

The transmission of signals and power between multiple layers is strong in blind vias PCB. Here are some of the uses of blind vias in the design of the circuit board.

Thermal Regulation

Blind vias boards can conduct heat from the inside and outside layers. The heat dissipation qualities make the board suitable for a diverse range of activities.

Signal Routing

A blind via helps in boosting signal routing in circuit boards. The PCB design makes them suitable for use in high speed communication devices. They are particularly useful in dense boards that can withstand extreme temperatures.

Escape Routing

Blind vias are also used for escape routing. The special design of the vias allows fanout routing on medium and small size surface mounts.

Power Routing

Power routing is also possible with blind vias. They are used in the situation where the ground net requires high current output.

Selecting Blind Via PCB Design: Things to Consider

You need to consider certain factors when selecting via design. Here are some of the factors that you should consider when selecting a blind vias PCB solution for your project:

Blind Vias Size

One of the foremost considerations when selecting blind Vias PCBs is the size of the vias. The most common size of blinds is 10 mil. Micro blind vias are also available that have a size of just 4 mils. The thickness of the board required should determine the right size for the project.

Blind Vias Tolerance

Blind vias tolerance is another important consideration when selecting a PCB solution. You must select blind Vias with a high hole size tolerance. The via tolerance should support the appropriate technology. Consider asking the blind vias PCB provider about the stack that will support the technology.

IPC Guidelines

IPC guidelines must be followed when selecting blind vias PCB. The guidelines differ for Class 2, 3, 3Ds, and military grade technologies. The stipulations of the guidelines regarding the distance between the vias must be strictly followed.

Annular Ring

The annular ring refers to the area left after drilling through each layer pad. You should follow the annular ring requirements for the specific class of the PCB. The annular rings of the blind vias PCB should have enough area to maintain a strong connection to the trace on each layer.

Filling of Blind Vias

Blind vias must be covered using the right chemical. The fillings covering the layers must not have any type of defect. The vias can be filled with nonconductive or conductive paste. Whichever method is used, there must not be any entrapments of the chemicals within the holes.

Blind vias should be filled with electroplating substances of a particular specification depending on the project requirements. A conductive paste is recommended for filling the blind vias if the project requires the movement of heat from the upper to the lower side of the circuit board.

Blind Vias Sealing

Blind vias must be covered with capped plating. The mechanical processes and sequential buildup during the manufacturing of the product can disturb the plating which will cause performance issues. You must make sure that the blind vias are filled with resin before the plating process.

Application of Blind Via PCB

Blind vias PCB has various applications in different industries. PCBs with blind vias construction minimize the circuit board layers when creating the ball grid getaway channel.

With blind vias, the gateway channels on the internal layers can be increased without increasing the circuit board aspect ratio. The board aspect ratio and the drill size determine the smallest size of the blind vias hole.

Circuit board BGA parts feature different pitches. A board with a 4.0 mm radius has between 0.8 and 1.27 mm pitches.

An aspect ratio of the blind vias can be calculated by dividing the PCB thickness by the drill hole diameter. Drilling blind vias will minimize the aspect ratio due to the need for a less supported layer.

Building with Blind Vias PCB

Blind vias PCB are constructed of multiple layers with holes made using the drilling method. The construction of blind vias facilitates a strong connection between multiple layers of the board. You must contact the manufacturer to know the technical details of the blind vias PCB.

Adding blind vias requires meticulous planning. Trying to add blind vias on the go will create spacing issues. You may have to abandon the circuit board and start afresh, which can be a waste of precious resources.

Blind vias of PCB start from one of the two sides of the board. The vias must be drilled evenly between the layers. The blind vias mustn't percolate the entire circuit board. Moreover, the blind vias must also not begin or end in the middle of the PCB.

The ratio between the blind vias hole height and diameter (H/d) must always be less than one. The ideal H/d value is 0.8. In addition, dielectric gaps are required for large blind vias PCBs.

Blind vias need to be drilled with precision within the main cores. The vias must reach the middle of the layer and be stacked between the layers.

During the building of the blind vias, holes are coated before combing the layers of the PCB. This generally requires extra lamination processes as compared to through hole vias. The additional processes result in more time and resources required to build blind vias circuit boards. The cost of manufacturing blind vias is also higher since more production processes are required. But the extra efficiency of the blind vias more than makes up for the high cost.

 The Use of Blind Vias in High Speed Digital Circuits

The applications of large and super large circuits within a circuit require the development of multiple layers. Blind vias are ideally suited for complex circuit board designs. Circuit boards with blind vias construction can meet the need for high speed and low volume integrated chips with a large volume of pins.

Unlike through board chips, the electric connections in blind vias PCB don’t circulate from the top to bottom. The result is increased transmission quality makes blind vias chips ideal for use in high performance applications.

With blind vias, the redundant stubs are minimum that increases the efficiency of the chips. The blind vias balance the cost and performance of chips due to high quality performance. The diameters of the hole result in improved impedance continuity that results in enhanced efficiency of the chips.

Performance Parameters that Affect the Use of Blind Vias

Blind vias allow efficient signal connection between interconnection lines from one layer to another. The blind vias are efficient electric conductors connecting and routing different layers.

Blind vias don’t circulate electricity throughout the circuit board. The made of blind vias allow efficient connection between the surface plane routing and internal PCB layers. The particular construction of the blind vias makes them an ideal solution in situations where signal integrity is important. The design of the digital systems must be optimized, and the quality of the signals improved through efficient design planning.

The electrical model of the blind vias in high speed circuits reflects the parasitic capacities. Moreover, the inductance of the blind via also affects the circuit performance.

Equivalent Electrical Model of Blind Vias

High speed blind vias have specific capacitance for the ground. The capacitance of blind vias is equal to the anti pad diameter, the thickness of PCB, substrate material’s dielectric constant, and the diameter of the pads.

Blind vias capacitance in high speed circuits slows down the circuit speed that prevents signals to rise beyond a tolerable level. The signals and the capacitance of blind vias are related to the impedance of the transmission level of Z0.

The inductance of blind vias is generated when signals pass through the vias at high speed. The inductance in the blind vias is greater than the capacitance of the vias. The inductance of the vias is equivalent to the length and diameter of the blind vias.

The equivalent impedance of the blind vias is also an important consideration. The electric performance of blind vias varies based on the design parameters. The pad and anti pad quality, length, and diameter impact the impedance discontinuity in the case of high speed circuits that affect the signal integrity.

The effective bandwidth of blind vias can be used to assess the performance of the signals when the attenuation insertion loss degree is not more than  3dB. In addition, simulation of TDR can help in the analysis of the reflection due to the impedance discontinuity.

An example can help understand the efficiency of the use of blind vias as compared to the through hole vias.

Examples of the Use of Blind Vias PCB

Blind vias can be applied when a signal line is necessary to circulate from one layer to another. Suppose that the radius of the blind vias is set to 0.1 mm while the length is set to 0.81 mm.

Through hole via connection radius is set at 0.1 mm and the length at 0.6 mm.

The simulation results show that the return loss of blind vias is up to 7 dB when the frequency range is between 40 GHz and 80 GHz. In comparison, the return loss of the through hole PCB design is greater up to 10 dB.

With blind vias, the parameter insertion loss is maximum with the frequency range of 76 GHz. The insertion loss with through hole vias is the largest with a lower frequency of 52 GHz.

Another important consideration is the operation bandwidth. With blind vias, the loss when the operation bandwidth is 22 GHz will be less than  3 dB. In contrast, the operation bandwidth of the through hole will be 15 GHz with an insertion loss of  2 dB. This shows that the blind vias operate with greater integrity with reduced loss.

The change category of the impedance of blind vias is generally between 46 and 52 while it is between 42 and 53 for through hole vias. It shows that better transmission line continuity of blind vias is better than the through hole vias.

The transmission quality and signal line connection between the layers is better for blind vias PCB. The parameter of the return loss throughout the hole, in contrast, lies within the range of 40 and 80 GHz, and the return loss is between 4 dB and 8 dB. The parameter return loss of blind vias is much lower, especially when the frequency range is high.

The parameter insertion loss of blind vias is much less than compared to the buried vias. The operation frequency is also lower resulting in improved performance. The operation bandwidth and the signal loss ratio are much greater with the use of blind vias PCB.

The characteristics of TDR of blind vias are also superior to the through hole design. The blind vias provide improved impedance continuity and transmission line quality resulting in more stable operations as compared to through hole design.

Relationship Between Blind Via Parameters and Signal Strength

An important consideration with the use of blind vias construction is the parameters of the hole. The depth, diameter, and platting of the hole impact the performance. A simulation example can help in understanding the influence of blind vias construction and signal strength.

Suppose that the radius of the blind vias is set at 0.1 mm with a variance between 0.1 mm and 0.175 mm. The simulation results show that the change in impedance of blind via is between 6 and 13.5 categories. The simulation also shows that the discontinuity impedance increases the insertion range loss. The largest attenuation with blind vias is recorded at 1.7 dB when the signal frequency is between 20 and 60 GHz.

The change of impedance is between 10 and 17 when the blind vias radius changes from 4 to 7 mil. The largest attenuation is 1.6 dB when the signal is between 20 GHz and 60 GHz. The initial value of the construction of the blind via is 0.2 mm and it lies between 0.2 and 0.28 mm.

As per the simulation results, the change in impedance with blind vias is between 6.5 and 10.5 when the radius changes from 0.2 mm to 0.28 m. The largest attenuation with blind vias is by 2 dB at this point. The change of impedance is between 10.5 and 15.5 at this range of radius. The impedance discontinuity increase results in higher insertion loss. Moreover, the attenuation loss increases by 3.2 dB with the given parameter.

Let’s suppose that the parameters of the blind vas are unchanged and the anti pad initial value is set at 0.3 mm which fluctuates between 0.3 mm and 0.375 mm. The simulation results show that at this point the size of the impedance of the blind via reduces to 5.5 in this category. The impedance discontinuity and the insertion loss decrease. The largest attenuation is recorded at 3.2 dB. As the size of the blind vias anti pad changes between 0.3 mm and 0.375 mm, the impedance will decrease from 10 to 7.5 with the largest attenuation reported at 3 dB.

The use of 8 layer blind vias PCB shows improved efficiency when the parameters are the same. The improved efficiency is possible due to a more efficient design of the blind vias. PCBs with blind vias design are efficient in heat dissipation making them ideal for use in high speed designs.

The characteristics of blind vias design make them the perfect choice for use in complex boards with multiple layers. The blind vias circuit board is more efficient in terms of signal retention and impedance as compared to the through hole design.

Blind vias PCB have lower insertion loss and improved impedance discontinuity as compared to the alternative. The low insertion loss and improved impedance discontinuity allow blind vias circuits to be used in complex environments. The blind vias PCB have wider operation bandwidth making them ideal for high speed communication.

The diameter and size of the hole are important determinants of the quality of the circuit boards. The signal strength is high and the loss is minimum with blind vias circuits. The attenuation of signal loss is also minimal due to the higher diameter and pad size of blind vias circuits. The increase in the diameter results in reduced signal insertion loss while the impedance discontinuity increases. 

Use of Blind Via Products

Blind via PCB products can be used in a number of different situations. Here are some of the situations where blind vias PCBs are the ideal solutions:

Greater Insulation Requirements

Blind vias are ideal for use when there is a need for high insulation. Electrical components are high speed 5G devices that can benefit from blind vias design.

The design of blind vias makes them ideal for situations where high heat dissipation is required. The dielectric factor (DF) of blind vias PCB products is low. This means that the design allows more energy without excessive heat ups.

The DF of blind vias PCBs is less than 0.0023. The extremely low dissipation makes them excellent for use in extreme operations.

High Speed Connections

Blind vias are perfect for IT components that require high speed connections. 5G devices can benefit from the use of blind vias PCB.

PCBs with blind vias design have smaller widths with minimum capacitance resulting in lower degradation of the signals even at high speeds. The signal discontinuity is minimum with blind vias PCBs with lower signal reflection.

The inductive signal discontinuity results in high power integrity that makes them perfect for use in high speed networks with a speed of more than 5GB/s.

High Quality Data Transmission

The low dielectric constants (Dk) results in improved signal loss dissipation. In other words, the loss of signals during data transfer is reduced as a result of a low DK. The Dk value of blind vias is about 3.7, resulting in high electrical conductivity and minimum signal loss.

The construction of the blind vias PCB makes them perfect for a wide range of applications. The dielectric loss is low which leads to reduced transmission loss. This makes blind vias PCBs suitable for use in a wide range of applications.

Performance at Extreme Temperatures

Blind vias are also best suited for use in extreme temperature operations. The particular design of the circuit boards results in minimum damage during operations. The integrity of the data is preserved at high speed data transmission.

Due to the low dielectric constant, the loss with blind vias is low. The low transmission loss property makes it suitable for use in a lot of different situations:

High Laminate Resiliency

Blind vias PCB are ideal when there is a need for high laminate resiliency. The circuit boards with the blind vias design have high endurance in extreme conditions. The high endurance makes the laminate withstand stressful environments with less damage incurred.

The connection between the blind vias layers is strong. The high laminate resiliency means that there is a greater bond between the layers. The result is that the PCB component can be used in different situations where there is high electrical or mechanical stress.

Reliable Performance

Blind vias PCB products are recommended when there is a need for meeting strict quality requirements. The product can be used in situations where the laminate has to comply with specific thresholds.

The product meets the requirements of reliable quality standards. The laminate material can be installed in different situations where reliable performance is required.

High Signal Integrity

PCBs with blind vias construction can be used in situations where high signal integrity is required. Printed boards with the design can work with minimum loss in signals. The special construction of the boards allows multiple routing options since the inner layer doesn’t run throughout the boards. This results in minimum signal degradation even at high speeds and temperatures.

Circuit boards with blind vias design can be used in sensitive electronics that require precise signal strength. The boards are ideal for the manufacture of medical and military devices that require high quality build to withstand varied conditions.

The high conductivity of the blind vias PCB makes them efficient in absorbing heat buildup. Less heat build up means the efficient flow of data.

Long Lasting Performance

PCBs made of blind vias are also ideal for making durable electronic components. The lamination allows efficient operation with low damage to the internal components. The damage is minimized since the connected components aren’t exposed to high heat.

Blind vias design allows heat to be dissipated without damaging the critical components. This ensures efficient operation with minimum interference. The product can operate in extreme conditions and continue to operate for a long time.

Blind vias lamination results in minimum mechanical and electrical disturbances. As a result, the product continues to operate efficiently and maintain optimum performance for a long time.

Assessing Requirements When Selecting a Supplier

You should thoroughly assess your requirements about the use of blind vias. Make sure that you ask the supplier about the use of blind vias. Know about the parameters such as hole diameter, depth, impedance, and other characteristics of the construction of the blind via. Knowing what to look for based on the use of the blind vias will help you select the right product.

Here are some other considerations that need to be accounted for when buying blind vias. You must make sure that the product is up to mark and meets your requirements.

Cost and Delivery

Set budgets are important for any firm. You must make sure that the prospective blind vias PCB provider will supply you with the product at the right cost. You must ask the supplier about the exact cost. Enquire about hidden costs that will affect the final quote.

You must also establish a clear line of communication regarding the delivery of the blind vias. You must make sure that the manufacturer will deliver the blind vias in the required quantity and quality.

Ask the supplier if the quoted figure for blind vias PCBs includes the shipping cost. You should ask whether the delivery will be made in single or multiple batches. Ask the supplier whether speeding up the delivery process will increase the cost.

Purpose of Blind Vias

Make sure that blind vias can be used for their intended purpose. Ask the supplier of the blind vias whether the product can be used in a specific project. You should inform them about the specific operational characteristics to figure out if blind vias PCBs are suitable.

Quality assurance is important to ensure that the blind vias can be used for the intended purpose. You should ask the supplier whether the blind vias adhere to the quality standards.

Consider sending a survey to the suppliers to find out if the blind vias PCB solution will meet the operational requirements. You should purchase from vendors that provide the best assurance about the use of the blind vias.

The blind vias PCB solution provider must provide quality assurance about the intended use of the product. You should make sure that the blind vias solution provider has the required quality product. The product must meet all types of quality standards including ISO 9001 2015 series that relate to the quality systems models.

Conclusion

The attenuation of the signal insertion decreases with the increase in the anti pad size of blind vias. Moreover, the impedance discontinuity also decreases with the increase in the anti pad size. The simulation example shows that the effective operation bandwidth becomes 20 GHz when the insertion loss is no more than 3 dB and the radius of the blind vias is less than 0.23 mm.

Changes in the impedance of the blind vias in a controlled environment are recorded to be within 10 percent. The radius of the blind vias must be kept below 0.125 mm while the pad should be no larger than 0.25mm.  The blind vias antipode must also be kept at less than 0.275mm for optimal performance.

You must consider different factors when searching for blind vias PCB solutions. Supplier expertise and certifications are important to ensure that you get the best quality blind vias solution. Industry experience is also an essential consideration.

Blind vias PCB products can be used in different situations. You must make sure that the product meets strict quality standards. The blind vias meet strict quality requirements for use in high speed communication products. The PCB design involves the best quality layout, assembly, and fabrication.

Hemeixin PCB offers a range of solutions that meet quality specifications. We have worked with leading industries all over the world supplying them with the best quality and high value end to end products.

Check Hemeixin PCB to get more information about our products. You should get in touch with our customer service representative to get in depth information about the use of blind vias PCB solutions.