Multilayer PCB soft as rigid as a multilayer PCB, multilayer lamination technology, can be made into a multi-layer flexible PCB. The easiest multilayer soft-sided PCB PCB is covered with two layers of copper on both sides to form a shield of three soft PCB. This is equivalent to three soft PCB coaxial wire or shield wire on the electrical characteristics. The most common structure is a four-layer PCB multilayer flexible structure with metallized holes to achieve the interconnection between layers, the middle floor general is the power and ground planes.
Advantages multilayer PCB soft base film is lightweight and has excellent electrical characteristics, such as low dielectric constant. Multilayer flexible PCB board made of polyimide film to the substrate than the weight of rigid epoxy glass cloth multi-layer PCB board about 1/3 lighter, but it lost its single-sided, double-sided flexible PCB fine The flexible, most of these products are not required to be flexible.
Multilayer PCB soft can be further divided into the following types:
1) is formed on a flexible insulating substrate a multilayer PCB, which is defined as the finished product can flex: This structure is usually one or both sides of the microstrip many flexible PCB bonded to both surfaces of the end, but its center and bonding together the end portions, so as to have a high degree of flexibility. In order to have the desired electrical characteristics, such as characteristic impedance performance and rigid PCB interconnect it matches, each wire layer of the multilayer flexible PCB components, the design must be in ground contact surface of the signal line. In order to have a high degree of flexibility, the layer may be a thin wire, a suitable coating, such as polyimide, instead of a thick layer of laminated cover layer. Z metallized holes so that the surface between the flexible wiring layer may achieve the desired interconnection. This multi-layer flexible PCB best suited for applications requiring flexibility, high reliability and high density designs.
2) constituting the multilayer PCB in the flexible insulating substrate, the end of which the finished product can be predetermined deflection: These soft multi-layer flexible PCB is an insulating material, such as a polyimide film, a laminate made of plywood. After lamination losing inherent flexibility. When the design requirements to maximize the use of the insulating film properties, such as low dielectric constant, the thickness of the homogeneous medium, light weight and capable of continuously processing characteristics, on the use of such a flexible PCB. For example, a polyimide film with a multilayer PCB insulating material about epoxy glass cloth weight is lighter than the third rigid PCB.
3) constituting the multilayer PCB in the flexible insulating base material, the finished product must be shaped, rather than continuous flexing: These soft multi-layer PCB is formed of a soft insulating material. Although it uses a soft material, but due to restrictions of the electrical design, as for the required conductor resistance, require a thick conductor, or for the desired impedance or capacitance, between the request signal layer and the ground layer has a thickness The insulating spacer, therefore, it is applied when the finished product has been formed. The term "formable" is defined as: a multi-layer flexible PCB member has the ability to make a desired shape, and in the application can not be deflected. Application avionics unit internal wiring. In this case, the requirements of the stripline conductor or three-dimensional design of low resistance, capacitive coupling or circuit noise and minimal interconnection end portion can be smoothly curved in a 90 °. Multilayer PCB soft polyimide film material implements this routing tasks. Because high temperature polyimide film, there are flexible, and good overall electrical and mechanical characteristics. To achieve this all the interconnecting member section, wherein the alignment portion is further divided into a plurality of multi-layer flexible circuit member, and together with the adhesive tape to form a printed wiring bundle.
