16+ Years Experience in PCB Manufacturing
What is Blind and Buried Vias PCB?
Plated through holes (PTH) are the vias from top to bottom layers. But blind vias are the vias from the outer layers (either the top or bottom layer) to the inner layers. When both sides of the vias are buried in the inner layer of the PCB, they are called buried vias. Thus, buried vias can’t be seen after the PCB is manufactured. We take the following 6-layer HDI PCB as an example: there are blind vias from layer 1 to layer 2, buried vias from layer 3 to layer 4, and plated through holes from layer 1 to layer 6. So blind and buried vias are commonly used in high-density PCBs, also called high-density interconnect PCBs.
So a printed circuit board with blind and buried vias are called Blind and Buried Vias PCB.
Get a free quote now!
Why Do Blind and Buried Vias Emerge in the PCB Manufacturing Industry?
Why do blind and buried vias emerge in PCB fabrication? This answer should start from a traditional multilayer printed circuit board. The structure of the standard multilayer PCB has outer layers and inner layers, to achieve the inner connection function between every circuit layer, you should use plated through via holes and make the vias metallization. But you know the size of the printed circuit is limited, so if you want to achieve more function and put more high-performance parts in the board in PCB assembly, you have to add more circuit lines to the board.
Except for making thinner circuit line width, the DIP plug-in via size zooms out from 1 mm to SMD 0.6 mm and further zooms out below 0.4 mm. But it still will occupy the surface area of PCB, so blind and buried vias emerges in a few high-tech PCB board manufacturer as the times require.
When Do Blind and Buried Vias Emerge in the PCB Manufacturing Industry?
When do blind and buried vias emerge in PCB fabrication? From the end of 20 century to the beginning of 21 century, the printed circuit board electronics industry has had rapid development in technology. In the meantime, electronic techniques improved rapidly. So to meet the customer’s requirements continuously, the printed circuit board industry must follow the development step of the circuit board electronics industry.
And every person will like more small and exquisite products, so electronic products constantly update. Along with the volume of electronic products becoming smaller, lighter, and thinner, print circuit boards are developed into flex PCB, rigid-flex PCB, blind via PCB and buried Via PCB, etc., to satisfy the requirement of electronic products.
What Makes Blind and Buried Vias Important?
Introduction to Buried Vias
Introduction to Blind Vias
What is the Difference Between Blind and Buried Vias?
Many Benefits of Blind and Buried Vias
1. The use of blind and buried vias is an effective way to increase the density of multi-layer boards, reduce the number of layers and the size of the boards, and significantly reduce the number of plated through holes.
2. Using blind and buried vias increases reliability, improves the characteristic impedance control, and reduces crosstalk, noise, or distortion.
How Blind and Buried Vias are Made?
The fabrication process of blind via PCB has three different methods, as below:
Mechanical specified the depth drilling:Produce the PCB production by traditional multilayer PCB process till finished the lamination. Use a drilling machine to set the z-axis depth to drill the desired depth. This method is relatively simple but has a few problems:
Step 1： the four inner layers (layers 3-6) are made in the way of a general 4-layer PCB with PTH, and blind layers 1-2 and 7-8 are produced as normal double-sided PCB;
Step 2： Laminate all the layers together: the inner 4-layer PCB and 2 pcs of 2-layer PCB, then we get eight layer PCB;
Step 3: Produce the 8-layer PCB as standard double-sided PCBs, drill the PTH holes, copper plating, solder mask, etc.
Step 1： laminate layers 3-6, produce the copper trace and PTH as standard 2-layer PCB;
Step 2： laminate layers 2-7, and laser drill layers 2-3,6-7, produce copper trace, and plate the vias;
Step 3： laminate layers 1-8 and laser drill layers 1-2,7-8, produce copper traces in the outer layers, and plate the vias.
Any layer lamination and drilling
This method is so popular that almost the global blind via and buried via PCB fabrication industry uses it now. A lot of big PCB manufacturers can do that.
This method is an expansion of sequential lamination/drilling mentioned above(the B method), but the difference is to add layer by layer from the inner to the outside of the board. Normally it begins from layer 2 of PCB in the middle and uses the blind holes by laser drilling to connect all the additional layers. These vias are stacked micro vias or staggered micro vias. Stacked via means the via is precisely on the top of the via from the other layer, but staggered via is not. This kind of PCB is called any layer PCB. There are three ways to do any layer drill below:
Use photosensitive resistance and the permanent media layer simultaneously, then aim at a specific location, make exposure and development with the negative film to expose the bottom copper pad and form a bowl-shaped blind hole, and then thoroughly add chemical copper and copper plating. Then the circuit of the outer layer and the blind via are etched out. Or you don’t need to make copper plating to complete the conduction, fill in copper paste or silver paste also has the same result. Of course, you can add the other layers in the same way in the PCB manufacturing process.
Plasma Etching:This is the done company’s patent, so they named its business name to the demonstrate method.
Laser Ablation:In the HDI PCB manufacturing processes, there are three categories: CO2 laser, which is more commonly used, and Excimer laser and Nd: YAG laser.
Laser Drilling Introduction
Laser drilling technology has advantages such as high accuracy, strong versatility, efficiency, low cost, remarkable comprehensive technical and economic benefits, etc. Now, this technology has become one of the key technology in the modern PCB manufacturing field. Before the laser appeared, only can use high hardness material punched holes in lower hardness material. That makes drilling holes in high-hardness diamonds become complicated things. After the laser appeared, this kind of drilling became quick and safe. But, the hole drilled by laser is conical, not cylindrical like mechanical drilling. This is very inconvenient in some places. Programmable control of graphic output through the galvanometer.
Laser drilling is the process that focuses the laser on becoming a high-intensity heat source to heat the material that should be drilled into holes, melting the material in the laser action area or vaporization, then evaporation, then becoming holes. Laser beams are highly concentrated in space and time, and using the lens to focus can reduce the spot diameter to the 5th power of 10 ~ the laser power density of the 15th power of 10 w/cm2. Such a high power density can laser drill holes in almost any material.
Laser drills, as a kind of blind via in HDI PCB, have their characteristic in PCB fabrication:
Blind Vias and Buried Vias Electroplating
A, Under normal circumstances, any layer of copper just can make one-time whole board electroplating + one-time Pattern Plating.
B, Under normal circumstances, after the lamination process, the board thickness greater >= 80MIL, the through hole board will need whole board electroplating + Pattern Plating, so when the blind via plating, the outer layer can’t make whole board electroplating in PCB manufacturing.
C, After meeting the conditions above, the electroplating of blind vias needs to make as below:
1, If the trace width of the outer layer is greater than 6 MIL, at the same time, the thickness of the PTH board is less than 80 MIL, then the outer layer can make whole board electroplating in the electroplating process of blind vias.
2, The trace width of the outer layer is greater than 6 MIL, but the thickness of the PTH board is greater than 80 MIL, the outer layer should film sticking in the surface to protect the outer layer in the electroplating process of blind vias.
3, The trace width of the outer layer is less than 6 MIL. At the same time, the thickness of the PTH board >= 80 MIL, the outer layer should film sticking in the surface to protect the outer layer in the electroplating process of blind vias.
Important Things in Blind and Buried vias Production
How to Confirm and Recognize Blind and Buried Vias from Gerber Files?
How Is a Multilayer PCB Built?
Concise process flow of the multi-layer PCB: cutting and grinding → drilling positioning holes →graphics of inner layers → etching in inner layers→ inspection → blackening → lamination → drilling → plated through hole→graphics of outer layers → gold plating, de-filming etching → secondary drilling → inspection → solder mask → silkscreen → punching → testing → inspection
Choosing a Printed Circuit Board Manufacturer
1. Viasion has a strong technical force, a high-quality technical management team, and advanced automatic production and testing equipment. That means we can provide a strong guarantee for product quality and delivery.
2. Viasion has many years of experience in market operation and sales service as well as a perfect management system and has won a good reputation among customers.
3. The price of our products is advantageous and our raw material supply channel is guaranteed. To pursue the high quality of our products, we have passed the ISO9001 certification and all our products can meet the requirements of RoHS and REACH standards.
Get an Instant Online Quote Today
Viasion Technology is your trusted partner & one-stop shop for PCB fabrication, components sourcing, PCB assembly and electronic manufacturing. With more than 16 years of experience, we have been supplying high-quality PCBs with competitive pricing for 1000+ customers worldwide. Our company is ISO9001:2015 Certified & UL Listed, and all our products are 100% E-tested and inspected by AOI & X-RAY to meet the highest industry standards. So please get an instant quote from our sales team now, and we will take care of the rest.
Frequently Asked Questions
Blind vias: When only one side of the vias is in the outer layer of the PCB, they are called blind vias.
Buried vias: When both sides of the vias are buried in the inner layer of the PCB, they are called buried vias.
Blind via and buried via are normally used in high tech electronic circuit boards, such as cellphone PCBs. We normally call this kind of blind buried via board with small drill holes and trace width as HDI PCBs.
Blind and buried vias can be created by the following three methods.
Mechanical drilling with fixed depth
Build up Process
Here we only talk about laser drill blind via holes. PCB blind via fabrication process as following: 1) finish all inner layers first; 2) laminate two out layers prepreg and copper sheet on the ready finished inner layers PCB board; 3) drill the blind via in PCB by laser. Please note accuracy is very important for the blind via in pad.
The benefits of using blind and buried are stated below:
Reducing the size and weight of the PCB
Reducing the number of the layers
Improving the electromagnetic compatibility
Increasing the characteristics of electronic products
Making the design work easier and faster
The miniaturization of the diameters of blind and buried vias places higher demands on the shape of these vias.
The miniaturization of the diameters of blind and buried vias brings many difficulties to the plating of these vias.