, especially those with more than 20 layers, play a crucial role in many fields due to their excellent electrical performance, powerful wiring capabilities, and high-density integration characteristics. Whether it is a 5G base station in the communication field, a high-end image diagnostic instrument in medical equipment, a auto drive system system in automotive electronics, or an aircraft control module in aerospace, it can not be separated from the support of high multilayer boards.
1, Analysis of processing difficulties
(1) Difficulties in the production of inner circuit
With the increasingly diverse functions of electronic products, the requirements for the inner layer circuits of high multi-layer boards are becoming more stringent. The line not only needs to meet the requirements of high-speed signal transmission, but may also involve thick copper design to carry high currents or high-frequency characteristics to adapt to specific frequency bands. For example, in some high-end server motherboards, the inner layer circuitry needs to ensure stable transmission of a large amount of high-speed data signals, which places extremely high demands on the rationality of inner layer wiring and precise control of graphic size. At the same time, when the number of inner signal lines is large, the line width and spacing are reduced to 4mil or even smaller, and the board layers are multiple while the core board is thin, wrinkling is prone to occur during the production process, which undoubtedly greatly increases the cost and difficulty of inner circuit production.
(2) Difficulty in alignment accuracy between inner layers
The increase in the number of layers makes the alignment accuracy between the inner layers of high multi-layer boards a challenging issue. The temperature and humidity changes in the workshop environment can cause the film to expand and contract, and the core board will also experience similar size changes during the production process. These dual factors combine to make it even more difficult to control the alignment accuracy between the inner layers. Even extremely small alignment deviations, after being stacked in multiple layers, may cause wiring connection errors, seriously affecting the performance of the circuit board.
(3) The pressing process is complex and challenging
The stacking operation of multiple core boards and semi cured sheets in the compression process is full of risks. On the one hand, delamination is prone to occur, where the core board and PP are not fully bonded, resulting in interlayer separation; Skateboarding problems also occur from time to time, causing relative displacement between layers; In addition, if the problem of residual bubbles is not handled properly, it can form voids inside the board, affecting signal transmission and the mechanical strength of the board. Moreover, the increase in the number of layers makes it difficult to maintain consistent control over expansion and contraction, as well as size factor compensation. The thinning of the interlayer insulation layer also increases the risk of interlayer reliability testing failure.
(4) Drilling processing faces numerous obstacles
High Tg or other special plates are often used for multi-layer boards. Due to the differences in hardness and toughness of different materials during drilling, the roughness of the drilled holes varies greatly, which greatly increases the difficulty of removing the adhesive residue inside the holes. In high-density multilayer boards, the hole density is high and the drill bit frequently enters and exits, which not only reduces production efficiency but also easily leads to tool breakage. In addition, if the edges of different network vias are too close, it can also cause CAF effect problems, seriously threatening the long-term reliability of the circuit board.
2, Exploration of coping strategies
(1) Carefully selected materials
To cope with the challenges of processing high multi-layer boards, the first step is to start with material selection. With the development of electronic components towards high performance and multifunctionality, the performance requirements for electronic circuit materials have also skyrocketed. Copper clad laminate materials with low dielectric constant and dielectric loss, low coefficient of thermal expansion (CTE), low water absorption, and good comprehensive performance are preferred. High quality copper-clad laminates are the cornerstone of ensuring pcb quality, and their quality directly affects the performance and reliability of the product. For example, some well-known pcb manufacturers strictly select A-grade boards from brands such as Shengyi and Jiantao when producing high multilayer boards. Although these boards have relatively high costs, they provide a solid guarantee for the high reliability of the products.
(2) Inter layer alignment control
Size compensation and control: Through long-term production practice and accumulated data and historical experience, precise compensation of the graphic dimensions of each layer of the high-rise board is carried out to ensure the consistency of the expansion and contraction of each layer of the core board. This requires enterprises to establish a comprehensive production data management system, monitor and analyze various parameters in the production process in real time, and continuously optimize size compensation plans.
Advanced positioning method: Adopting high-precision and highly reliable interlayer positioning methods before pressing, such as four groove positioning, hot melt and rivet combination technology. These advanced positioning methods can effectively improve interlayer alignment accuracy and reduce line connection problems caused by positioning deviations.
Compression process and equipment maintenance: Reasonably set the compression process program and strengthen the daily maintenance of the press. Regularly check the key performance indicators of the press, such as pressure uniformity and temperature control accuracy, to ensure the stability and reliability of the pressing process, thereby ensuring the quality of the pressing.
(3) Optimization of compression process
Selection of positioning method: Based on different product structures, flexibly choose the appropriate interlayer positioning method before pressing. For example, for products that require extremely high interlayer alignment accuracy, four slot positioning technology can be given priority consideration; For some products with complex structures that require consideration of multiple factors, a positioning method combining hot melt and rivets can be used.
Equipment and material matching: Select high-performance matching presses, which usually have excellent machining accuracy, reliability, and low failure rate. At the same time, with high hardness and flat imported steel plates, as well as high-quality PP sheets from Shengyi and supporting professional equipment, it provides hardware guarantees for the quality of compression, effectively avoiding process defects such as delamination, sliding plates, and residual steam drums.
(4) Drilling process innovation
Parameter optimization: In view of the problem of excessive thickness of the board and copper layer caused by the stacking of various layers in the high multi-layer board, which leads to severe wear of the drill bit, it is necessary to adjust the drilling parameters appropriately. For example, reducing the number of holes, falling speed, and rotational speed reasonably can reduce the wear of the drill bit and lower the risk of tool breakage.
Technological upgrade: With the increasingly fine line shape of printed circuit graphics and the continuous reduction of micro hole spacing, traditional mechanical drilling methods are gradually unable to meet the requirements. Laser imaging technology, as an emerging drilling process, has the advantages of high precision, fast speed, and minimal damage to the board. It can effectively solve many problems in drilling high multi-layer boards and has gradually become the mainstream process technology in HDI plate making.