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PCB Tech

PCB Tech

PCB Tech

PCB Tech

PCB moves toward high-density and refinement, four types of products receive the most attention
2021-10-07
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Author:Downs

At present, PCB products have begun to move from the traditional to higher density HDI/BUM boards, IC packaging base (carrier) boards, embedded component boards and rigid-flex boards. PCB will eventually go to the "printed circuit board". "Limit", in the end, will inevitably lead to a "qualitative change" from "electrical transmission signals" to "optical transmission signals", and printed optical circuit boards will replace printed circuit boards.

    Due to the rapid development of miniaturization, high performance, multi-function and high-frequency (speed) signal transmission of electronic products, the PCB must quickly move from the traditional PCB industry to products characterized by high density and refinement. develop. PCB products have begun, partly or fully, towards high-density interconnect build-up board (HDI/BUM) boards, package base (carrier) boards, integrated (embedded) component printed boards (ICPCB) and rigid-flexible printing Board (G-FPCB). In the next period of time, these four PCB products will surely become the four highlights of the PCB industry. In the future, more advanced printed optical circuit boards that use "optical signals" for transmission and calculation will replace the current ones that use "electrical signals." The printed circuit board for transmission and calculation.

    HDI/BUM board with core board production value accounted for 95%

    HDI/BUM boards are a type of PCB with higher density than conventional printed boards, and can be divided into two categories: HDI/BUM boards with "core board" and without "core board".

pcb board

    The HDI/BUM board with a "core board" is a PCB formed by a number of higher-density interconnection "layers" on one or both sides of a "conventional printed board". In fact, HDI/BUM boards with core boards are a structural form of "transition" from "conventional printed boards" to higher-density PCBs to meet the requirements of very high-density mounting. At the same time, regardless of equipment, process technology and management, it is also the best way to better adapt to the transition from the original PCB industry to very high-density PCB products. If the existing PCB production equipment, testing and technology can be improved slightly, development and production can be carried out, with low investment, low cost, and good continuity and scalability of management and production, so it is greatly improved. Accepted by most PCB manufacturers, therefore, HDI/BUM boards with core boards account for about 95% of the current output value of HDI/BUM boards.

    HDI/BUM board with core board, its high-density improvement is significant and prominent, such as the use of 4+12+4 HDI/BUM board with 200×300cm2 compared to 400×450 cm2 with 46 layers of buried/blind vias. The board has higher capacity, better electrical performance and reliability and service life.

    At present, most HDI/BUM boards without a "core board" use conductive adhesive technology, and their use range is limited, so the proportion is very small.

    IC packaging substrate is the most important to solve the CTE matching problem

    IC packaging substrates are developed on the basis of HDI/BUM boards by continuing to "deepen (high-density)", or the IC packaging substrates are HDI/BUM boards with higher density. In fact, the primary problem of IC packaging substrates is the matching (compatibility) with the CTE (coefficient of thermal expansion) of the packaged components (components) to be packaged, followed by the problem of high density.

    In essence, PCB is to provide interconnection and mechanical (physical) support for element (group) components. In today's electronic packaging market, there are mainly three types of packaging: (1) organic substrate packaging; (2) ceramic substrate packaging; (3) ideal size and speed (ie chip-level) packaging, such as crystal Wafer Level Package (WLP) and Direct Die Attach (DDA). Obviously, conventional PCBs do not have these advanced packaging (low CTE occasions) capabilities. Therefore, the PCB industry must develop technologies and products capable of these advanced packaging substrate materials.

    The CTE matching (compatibility) problem between the package substrate and the package element (assembly). When the CTE of the two do not match or differ greatly, the internal stress generated after soldering and packaging will threaten the reliability and life of electronic products. Therefore, the problem of CTE matching (compatibility) between the package substrate and the packaged components (assembly) is demanding that the CTE difference between the two becomes smaller and smaller as the mounting density increases and the area of the solder joints shrinks.

    The IC package substrate is mainly reflected in:

    1. The CTE of the substrate material is smaller or matched, that is, the CTE of this type of IC substrate should be significantly reduced, and be close to (compatible) the CTE of the chip pin to ensure reliability;

    2. It is directly used for the packaging of bare chip (KGD), so higher density of IC substrate is required;

    3. The thickness of the package substrate is thin and the size is small, most of which are less than 70mm×70mm;

    4. Most use thin low CTE substrates, such as PI materials, ultra-thin glass fiber cloth and carbon fiber CCL materials.

    Integrated component PCB while embedding active and passive components is the way out

    With the development and progress of high-density electronic products, high-frequency signal transmission and high-speed digitization, the number of chip I/Os and the number of passive components have increased rapidly, which has increasingly severely affected the reliability and transmission of electronic products. The way out for signal integrity is to integrate (embedded) component printed boards.

    Development steps: integration (embedded) passive components (mainly capacitors, resistors and inductors, etc.)-→ integrated (embedded) active components (IC components)

    1. Embed passive components

    The number of passive components is increasing rapidly. The number of passive components will increase rapidly with the increase of IC component integration (or the number of I/Os), high-frequency signal transmission and high-speed digitization (Assembled active components/passive components are from 1:10—→ 1:20—→1:30—→1:50): Passive components occupy more and more board area (30%→40%→50%→70%), which affects high density; the number of solder points of passive components Increasingly, it affects the reliability of the connection, because the solder joint is one of the main faults of electronic products. The number ratio of various elements (groups) of conventional assembly is shown in the table.

    The increase of passive components will inevitably bring about problems. The increase of passive components has caused more and more solder joints, and the reliability of soldering has become lower and lower. Solder joints have always been the largest failure rate of electronic products; the electromagnetic interference generated by the loop formed by passive components has become more and more serious; The increase of source components increases the board size (area), etc., which adversely affects high-frequency and high-speed digital transmission performance.

    The use of embedded passive components can eliminate these effects and significantly improve the integrity and reliability of the transmitted signal.

    The embedded passive components can be divided into: embedded single passive components; embedded "integrated" (combined capacitors, resistors, etc.) passive components.

    2. Embedded active components.

    While embedding passive components, but also embedding active components (various IC components), is under development and trial, which is the road of future development.

    The growth rate of rigid-flexible printed boards will accelerate in the future

    In 2006, the output value of flexible (including rigid-flexible) printed boards accounted for 17% of the total output value of PCBs, and it will increase at a faster rate in the future. By 2010, it is expected to reach 25%-30%.

    Rigid-flex printed boards have many advantages, but the most important ones are: improved reliability in high-density connections (replacement of mechanical connectors, etc.); conducive to miniaturization; installation flexibility (bending or folding) and implementation Three-dimensional (3D) assembly; simplified installation process and maintenance; convenient post-processing, etc., all of which have obvious advantages. Therefore, it will develop with the development of miniaturization, high performance, and multifunction of electronic products.