2. Multilayer multilayer board manufacturing process
The main difference between BUM and the traditional PCB manufacturing process lies in the hole forming method. The key technologies of BUM mainly include the dielectric material used in the laminated insulating layer; the hole forming technology of microvia; and the hole metallization technology.
Layered insulating dielectric material
Due to the difference between the insulating layer material and the interconnection micro-hole processing method, dozens of different BUM manufacturing methods have appeared, but according to the difference of the laminated insulating dielectric materials used in various BUM manufacturing processes, it is representative and application comparison Mature processes can be divided into three types: resin coated copper foil (RCC) process, thermosetting resin (dry film or liquid) process, and photosensitive resin (dry film or liquid) process. These three processes are now in use. The latter two processes generally need to achieve metallization and circuitization through an additive process, which has high requirements for materials and corresponding technologies. The RCC process adopts the subtractive process to complete the wiring, does not require a large investment in equipment (the main investment is laser driller), and adapts to the traditional multilayer PCB manufacturing process, and the finished BUM board has good performance and reliability, so There are more and more manufacturers using RCC technology to make BUM boards, and the demand for RCC continues to increase. Taking the RCC process as an example, the more the number of buildups, the worse the flatness of the board surface. Due to this limitation, the buildup layer of BUM on the core board generally does not exceed 4 layers.
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