Introduction to the Manufacturing Process of Build-up Multilayer Boards (Part 1)

1. What is a build-up multi-layer board (BUM-PCB)?

Build up Multilayer PCB (BUM) refers to the insulation substrate, or the traditional double-sided or multi-layer board, which is coated with an insulating medium and then electroless copper plating and copper electroplating are used to form wires. And the connection holes are superimposed many times to accumulate and form the required number of multilayer printed boards. As early as the 1970s, BUM technology had been reported in the literature, but it was not until the early 1990s that the Japanese (Yasu) branch of IBM developed a photosensitive resin coating on the core board, and the photoinduced method was used to form the interconnection of the vias. It was only after the new method of manufacturing high-density circuit boards by the additive method that the new technology of wiring was successfully used in Thinkpad notebook computers. This new technology was first published in 1991. , called Surface Laminar Circuit, SLC (Surface Laminated Circuit Board), because this technology has created an unprecedented High Density Interconnect, HDI (High Density Interconnect) new ideas, Japanese electronics manufacturers have developed, and since then the BUM era in the history of PCB started.

BUM adapts to the requirements of electronic products to be lighter, smaller, thinner and shorter, and can meet the needs of new generation electronic packaging technologies (such as BGA, CSP, MCM, FCP, etc.), so it has developed very rapidly throughout the 1990s , mainly used in portable electronic products, such as laptop computers, mobile phones, digital cameras and MCM packaging substrates. In 1998, the world BUM microplate market was 1.1 billion U.S. dollars, and in 1999 it reached nearly 2 billion U.S. dollars. 90% of the market is concentrated in Japan, and in 2000 the market was close to 3 billion U.S. dollars. Domestic experts once predicted that the world BUM board has entered a development period; at present and in the next few years, the technological change and market competition in the PCB industry will revolve around the BUM board as the center and its surrounding industries (materials, equipment and testing, etc.) .

Corresponding to the Japanese first proposed BUM (Multilayer Multilayer Board), European and American countries later proposed HDI (high density interconnect). In fact, the two terms express almost the same conceptual connotation. According to IPC data, the definition of HDI includes the following: non-mechanical drilling diameter is less than 0.15mm (6mil), and most of them are blind holes (buried holes), and the ring diameter of annular ring, pad or land is less than 0.25mm (6mil), the holes that meet this condition are called micmovia; PCBs with microvias have a contact density of 130 points/inch2 or more, and the wiring density (set the channel width as 50mil) at 117 inches/inch2 The above is called HDI PCB, and its line width/line spacing (L/S) is 3mil /3mil or less. It can be seen that the most essential feature of build-up multi-layer boards is high-density interconnection (HDI).