Challenges in PCB Prototyping for High Multi-Layer Boards

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Multi-layer PCBs serve as the “core strength” in fields such as communications, medical, industrial control, security, automotive, power, aviation, military, and computer peripherals. As the product functions increase and the circuitry becomes denser, the production difficulty also rises.

Currently, the domestic PCB manufacturers capable of mass-producing high multi-layer boards are often foreign enterprises, with only a few domestic companies possessing the capability for mass production.

Producing high multi-layer boards not only requires significant investment in technology and equipment but also experienced production technicians. At the same time, introducing customer certification for high multi-layer boards involves strict and complicated procedures, resulting in a high entry barrier for this industry and a long cycle for industrial production.

Specifically, the main processing difficulties encountered in the production of high-layer PCBs are as follows:

Challenges in Inner Layer Circuit Production

Multi-layer board circuits have various special requirements such as high speed, thick copper, high frequency, and high Tg values, leading to increasingly stringent requirements for inner layer wiring and graphic dimensions. For example, in ARM development boards, there are many impedance signal lines in the inner layer, which increases the difficulty of ensuring impedance integrity during production.

The inner layer signal lines are numerous, with widths and spacing generally around 4 mils or smaller. The production of multi-layer boards with many layers and thin cores is prone to wrinkling, which increases the production cost of the inner layers.

Challenges in Inner Layer Alignment

As the number of layers in multi-layer boards increases, the alignment requirements for inner layers also become more stringent. The film is affected by the workshop’s environmental temperature and humidity, leading to expansion and contraction, which makes it more difficult to control the alignment accuracy between inner layers.

Challenges in the Lamination Process

The stacking of multiple cores and PP (prepreg) can easily lead to delamination, sliding, and air pockets during the lamination process. With more layers, controlling the expansion and contraction and compensating for dimensional coefficients becomes inconsistent; if the interlayer insulation is thin, it can easily lead to failures in interlayer reliability testing.

Challenges in Drilling Production

Multi-layer boards made of high Tg or other special materials have different roughness for drilled holes, which complicates the removal of adhesive residues within the holes. High-density multi-layer boards have a high hole density, low production efficiency, and are prone to drill breakage. When the hole edges are too close between different networks, it can lead to CAF effect issues.

Therefore, to ensure the high reliability of the final product, multi-layer board manufacturers need to control the production process accordingly.

Material Selection

Currently, the development of high performance and multifunctional electronic components requires electronic circuit materials to have low dielectric constant and dielectric loss, as well as low CTE, low water absorption, and better high-performance copper clad laminate materials to meet the processing and reliability requirements of high-layer boards.

The quality of the copper clad laminate directly affects the quality of the PCB, making the selection and judgment of the board materials particularly important. To enhance the high reliability of HDI, Huaqiu strictly selects Shengyi/JianTao A-grade materials. Although the cost is dozens of yuan more per square meter than niche materials, it is a fundamental guarantee for the high reliability of Huaqiu’s HDI.

Control of Interlayer Alignment Accuracy

The accuracy of size compensation for inner layer cores and production size control requires collecting data over time during production and historical experience to accurately compensate for the graphic dimensions of each layer of high-layer boards, ensuring the consistency of expansion and contraction of each layer of core boards. Choosing high precision and reliable interlayer positioning methods before lamination, such as four-slot positioning (Pin LAM), thermal melting combined with riveting, is essential. Setting an appropriate lamination process and routine maintenance of the laminating machine are key to ensuring lamination quality.

Lamination Process

Currently, the main interlayer positioning methods before lamination include: four-slot positioning (Pin LAM), thermal melting, riveting, and a combination of thermal melting and riveting, with different positioning methods used for different product structures. The lamination equipment uses high-performance matching laminators to meet the interlayer alignment accuracy and reliability requirements of high-layer boards.

Huaqiu has invested in introducing lamination machines manufactured by the renowned Japanese company (MEIKI) and other supporting equipment to form a lamination line for high-precision multi-layer PCB lamination at this stage. MEIKI has excellent processing accuracy and reliability with low failure rates. Coupled with high hardness, flat imported steel plates (one of the core accessories for lamination), and high-quality PP sheets from Shengyi (bonding sheets), along with specialized supporting equipment, it effectively avoids process defects and enhances lamination quality. Ultimately achieving the customer’s quality requirements: high reliability + high stability.

Drilling Process

Due to the thickness of the board and copper layers caused by stacking, drill bits wear out severely and are prone to breakage, necessitating a reduction in the number of holes, drop speed, and rotation speed. With the rapid development of microelectronics technology and the widespread application of large-scale integrated circuits, the manufacturing of printed circuit boards is evolving towards layering and multifunctionality. This leads to finer printed circuit patterns and reduced spacing of micro-holes.

Therefore, during processing, the previously used mechanical methods can no longer meet the requirements. Laser imaging technology has greatly simplified the process flow and has become the mainstream process technology in HDI manufacturing. The Mitsubishi laser drilling machine possesses superior processing capabilities, and its introduction can effectively improve Huaqiu’s productivity, achieving unmatched traceability efficiency, stable processing quality, and high processing positioning accuracy.

Meizhou Circuit Industry Association

Source:——Weiwenxin “Printed Circuit World”、PCBworld

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