Microwave multilayer printed board; laminate; ceramic board,technology
Microwave printed board refers to a microwave electronic component produced by a conventional rigid printed board manufacturing method on a specific microwave substrate copper clad board.
The current high-speed signal transmission lines for printed boards can be divided into two categories: one is high-frequency signal transmission, which is related to the electromagnetic waves of radios, and transmits signals with sine waves, such as radar, radio and television, and communication (mobile phones, microwave communications). , optical fiber communication, etc.; the other is high-speed logic signal transmission, this type of products are transmitted by digital signals, and are related to the square wave transmission of electromagnetic waves. This type of products has been mainly applied in computers and computers, and has been applied to In home appliances and communications electronics.
In order to achieve high speed transmission, there are clear requirements for the electrical characteristics of the substrate material of the microwave printed board. In order to achieve low loss and low delay of the transmission signal, it is necessary to select a substrate material having a small dielectric constant and a dielectric loss tangent, and generally has a ceramic material, a fiberglass cloth, a polytetrafluoroethylene, and other thermosetting resins.
Among all the resins, polytetrafluoroethylene has the smallest dielectric constant (εr) and dielectric loss tangent (tan δ), and is resistant to high and low temperature and aging resistance. It is most suitable as a high-frequency substrate material and is currently the largest amount. Microwave printed board substrate material.
In this paper, based on the brief introduction of the manufacturing process of two kinds of ceramic powder filled microwave multilayer printed boards, the lamination manufacturing process technology is discussed in detail.
2 microwave multilayer printed board material
The microwave multilayer printed board laminate manufacturing process technology of the following two kinds of high frequency dielectric materials is mainly studied. The first type is ceramic powder filled, glass short fiber reinforced polytetrafluoroethylene (PTFE) high frequency dielectric material (RT/duroid 6002 sheet); the second is ceramic powder filled thermosetting resin copper clad sheet (RO4350 sheet).
2.1 Ceramic powder filled microwave multilayer printed board manufacturing process
The process flow is shown in Figure 1. The following two high-frequency dielectric plate lamination process technologies are introduced.
2.2 RT/duroid6002 lamination process 2.2.1 Bonding sheet 3001
In order to manufacture a microwave multilayer printed board using a high frequency dielectric sheet RT/duroid 6002, the supplier developed an adhesive sheet 3001 suitable for a low dielectric constant high frequency dielectric plate of RT/duroid. It is a thermoplastic chlorofluoro copolymer with a low dielectric constant and a low loss tangent in the microwave frequency range.
2.2.2 Lamination process 1) Layout
The RT/duroid 6002 sheet and the bonding sheet are alternately stacked. In order to ensure the accuracy of the overlap between the layers of the multilayer printed board, a four-slot locating pin is used for the arranging. The lamination temperature and time are controlled by placing the thermocouple probe into the non-pattern area of the inner layer of the plate to be pressed.
When the press is in a cold state (usually the press temperature is lower than 120 ° C), the above-disposed and mounted plate is placed in the center of the press, the press is closed, and the hydraulic system is adjusted to obtain the desired pressure in the area to be pressed. In general, an initial pressure of 100 psi is sufficient, and then the full pressure is raised to 200 psi to ensure proper flow of the bonded sheet.
The laminator was started and heated to 220 °C. Under normal circumstances, the maximum heating rate is controlled so that the temperature of the upper/lower furnace plates differs by 1 ° C to 5 ° C.
Normally, it is kept at 220 ° C for 15 minutes to bring the bonding sheet into a molten state, and has sufficient time to flow and wet the surface to be bonded. For thicker slab structures, the holding time can be extended to 30 minutes to 45 minutes.
5) Cold pressing
The heating system was turned off and the laminate was cooled while maintaining the pressure until the furnace temperature dropped to 120 °C. The pressure was released and the template containing the laminate was taken out of the laminator.
2.2.3 Problems and countermeasures
1) Bond failure
2) Spotted or blistering on the surface of the laminate
The reason is that the applied pressure is not uniform, the temperature is not properly controlled, and the inner layer of the inner layer is insufficiently cleaned and dried before lamination. The countermeasures are to use a clean template or other smooth materials, check the flatness or pressure. The laminate temperature profile was again tested using a thermocouple. Review the cleaning and drying procedures for the individual sheets to be pressed, while reviewing the storage conditions and time of the individual sheets during preparation and bonding.
The reason is that the temperature is too high or the pressure is uneven, and the temperature and pressure should be precisely controlled.
2.3 LA4350 lamination process
2.3.1 Prepreg RO4403
In order to achieve effective bonding, a prepreg RO4403 was selected for the RO4350 material.
2.3.2 Lamination process 1) Main process parameters Temperature: 175 ° C; Pressure: 40 kg / cm 2 ; Time: 2 hours;
Buffering method: 24 sheets of kraft paper for each of the upper and lower pads;
Mode of entry: use lower temperature (100 ° C) to enter the mold, 175 ° C to calculate the lamination time;
Pressure release method: adopt the sectional release pressure method.
After lamination under the above conditions, the interlayer bonding force can still meet the requirements, but the flatness of the laminate is poor. After several trials and with reference to the lamination characteristics of the prepreg RO4403 used, it was decided to laminate using the following process parameters.
2) Layout method
From bottom to top, stainless steel mold bottom plate/polyester sheet/4 RO4350 single piece/one prepreg RO4403/3 RO4350 single piece/2 prepreg RO4403/2 RO4350 single piece/1 prepreg RO4403/1 RO4350 Single piece / polyester sheet / stainless steel mold top cover.
24 sheets of cushioned kraft paper per side. The heating temperature was 175 °C. The pressure was 40 kg/cm2 (for a selected 30.48 cm x 25.4 cm (12 inch x 10 inch) mold, the pressure was 31 tons). The mold was introduced at room temperature and gradually heated. The holding pressure is 2 hours, and the pressure release mode is cooling and segmental release pressure.
During actual lamination, the temperature inside the platen is monitored and measured.
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