**Sequential Lamination Method: The Generation and Technical Requirements of Buried/Blind Vias**
From the early 20th century to the beginning of the 21st century, advancements in electronic housing technology have been rapid, and electronic assembly techniques have seen significant improvements. In order for the printed circuit board (PCB) industry to keep pace with these developments, it must evolve in parallel to meet customer demands. With the increasing trend for smaller, lighter, and thinner electronic products, the PCB industry has seen the emergence of flexible boards, rigid-flex boards, and buried/blind-hole multilayer PCBs, among other innovations. However, the investment required for PCB production equipment is substantial, particularly for the machinery used to produce multilayer PCBs with buried/blind vias, such as laser drilling machines and pulse plating equipment. For small and medium-sized enterprises (SMEs), especially those that do not mass-produce buried/blind-via multilayer PCBs, such significant capital investment in equipment is often not feasible. Therefore, utilizing existing equipment to manufacture buried/blind-via multilayer PCBs holds significant value. This approach not only allows companies to expand their product offerings but also enables them to meet the needs of specific customer segments. This article discusses some of the challenges faced in this production process.
1. **CAD Wiring**
Using the traditional lamination method, followed by stepwise lamination based on the specific needs, this process is referred to as sequential lamination. It is important to note that this approach has certain technological limitations, specifically that interconnections cannot be made arbitrarily. Therefore, these limitations should be carefully considered when performing CAD wiring. First, it is advisable to use more buried vias; second, minimize the use of blind vias. If blind vias are necessary, the number of interconnections should not exceed half of the total layers. This will help reduce the number of laminations and simplify the processing complexity.
2. **Inner Layer Production**
When manufacturing multi-layer PCBs with buried or blind holes, some of the inner layers may have metallized holes, while others may not. These must be clearly identified and differentiated during production. The inner layer drilling program files should correspond to the inner core board labels, and this information must be clearly specified in the process documentation. The anti-corrosion treatment for the inner layers can be achieved using dry film or pattern electroplating, depending on the manufacturer’s practices and the process proficiency.
3. **Lamination**
After processing the inner layers, which may be darkened or browned, they can be pre-stacked and laminated. Attention should be paid to the following factors during this process: first, ensure the lamination sequence is correct; second, verify that the inner layers are correctly aligned during lamination; third, confirm that the resin in the interlayer prepreg is sufficient to fill the holes. When preparing the production specifications, it is essential to select the appropriate semi-cured prepreg type and quantity. Finally, ensure the copper foil thickness is suitable, as when blind vias are used, the patterns on both sides may not form simultaneously, leading to varying plating times.
4. **Outer Layer Graphic Production**
The process for producing outer layer graphics is similar to that for regular double-sided or multi-layer PCBs. However, it is important to note that due to the presence of blind holes, the copper foil thickness on the top and bottom layers may differ, which complicates the etching process. Compensation should be applied during photomask drawing to account for these differences. Additionally, due to varying copper foil thickness, there may be differences in stress, which can lead to warping of the finished board. The warping is more noticeable when there are multiple interconnected blind holes. To mitigate this, consider using core boards with different thicknesses in the stack-up design to balance the stresses and prevent warping in the final product.
From the early 20th century to the beginning of the 21st century, advancements in electronic housing technology have been rapid, and electronic assembly techniques have seen significant improvements. In order for the printed circuit board (PCB) industry to keep pace with these developments, it must evolve in parallel to meet customer demands. With the increasing trend for smaller, lighter, and thinner electronic products, the PCB industry has seen the emergence of flexible boards, rigid-flex boards, and buried/blind-hole multilayer PCBs, among other innovations. However, the investment required for PCB production equipment is substantial, particularly for the machinery used to produce multilayer PCBs with buried/blind vias, such as laser drilling machines and pulse plating equipment. For small and medium-sized enterprises (SMEs), especially those that do not mass-produce buried/blind-via multilayer PCBs, such significant capital investment in equipment is often not feasible. Therefore, utilizing existing equipment to manufacture buried/blind-via multilayer PCBs holds significant value. This approach not only allows companies to expand their product offerings but also enables them to meet the needs of specific customer segments. This article discusses some of the challenges faced in this production process.
1. **CAD Wiring**
Using the traditional lamination method, followed by stepwise lamination based on the specific needs, this process is referred to as sequential lamination. It is important to note that this approach has certain technological limitations, specifically that interconnections cannot be made arbitrarily. Therefore, these limitations should be carefully considered when performing CAD wiring. First, it is advisable to use more buried vias; second, minimize the use of blind vias. If blind vias are necessary, the number of interconnections should not exceed half of the total layers. This will help reduce the number of laminations and simplify the processing complexity.
2. **Inner Layer Production**
When manufacturing multi-layer PCBs with buried or blind holes, some of the inner layers may have metallized holes, while others may not. These must be clearly identified and differentiated during production. The inner layer drilling program files should correspond to the inner core board labels, and this information must be clearly specified in the process documentation. The anti-corrosion treatment for the inner layers can be achieved using dry film or pattern electroplating, depending on the manufacturer’s practices and the process proficiency.
3. **Lamination**
After processing the inner layers, which may be darkened or browned, they can be pre-stacked and laminated. Attention should be paid to the following factors during this process: first, ensure the lamination sequence is correct; second, verify that the inner layers are correctly aligned during lamination; third, confirm that the resin in the interlayer prepreg is sufficient to fill the holes. When preparing the production specifications, it is essential to select the appropriate semi-cured prepreg type and quantity. Finally, ensure the copper foil thickness is suitable, as when blind vias are used, the patterns on both sides may not form simultaneously, leading to varying plating times.
4. **Outer Layer Graphic Production**
The process for producing outer layer graphics is similar to that for regular double-sided or multi-layer PCBs. However, it is important to note that due to the presence of blind holes, the copper foil thickness on the top and bottom layers may differ, which complicates the etching process. Compensation should be applied during photomask drawing to account for these differences. Additionally, due to varying copper foil thickness, there may be differences in stress, which can lead to warping of the finished board. The warping is more noticeable when there are multiple interconnected blind holes. To mitigate this, consider using core boards with different thicknesses in the stack-up design to balance the stresses and prevent warping in the final product.
