Discussion on Manufacturing Technology of Microwave Printed Board (2)

3 Selection of Microwave Printed Boards

The choice of microwave printed board substrate should first consider its dielectric properties, but at the same time must also consider the surface copper foil type and thickness, environmental adaptability, processability and other factors, of course, there are costs.

3.1 Copper foil type and thickness selection

At present, the most commonly used copper foil thickness is 35μm and 18μm. The thinner the copper foil, the easier it is to obtain high picture precision, so a high-precision microwave pattern should use copper foil no larger than 18 μm. If a 35 [mu]m copper foil is used, excessively high pattern accuracy deteriorates the processability, and the defective product rate inevitably increases.
Studies have shown that copper foil types also have an effect on the accuracy of the graphics. Current copper foil types include rolled copper foil and electrolytic copper foil. Rolled copper foils are more suitable for producing high-precision patterns than electrolytic copper foils. Therefore, when ordering materials, you may consider selecting a rolled-up copper foil substrate board.

3.2 Environmental Adaptability Selection

Existing microwave substrates have no problem with the standard ambient temperature range of -55°C to +125°C. However, two considerations should also be considered. One is whether or not the pores affect the choice of substrate. For microwave plates that require through-hole metallization, the larger the coefficient of thermal expansion of the Z-axis of the substrate, the higher the thermal expansion coefficient of the substrate. The greater the possibility of fracture, so under the premise of meeting the dielectric properties, Z should choose the substrate with a small thermal expansion coefficient (see Table 1 to Table 4); Second, the impact of humidity on the choice of substrate, substrate The resin itself has low water absorption, but after adding the reinforcing material, its overall water absorption increases, and it will affect the dielectric properties when used in a high-humidity environment. Therefore, the material with small water absorption should be selected when selecting the material (see the table A to Table 4), or take structural measures to protect.

3.3 Machinability selection

As design requirements continue to increase, some microwave printed board substrates have aluminum backings. The appearance of such aluminum-lined substrates brings additional pressure on the manufacturing process, the graphic production process is complicated, the shape processing is complicated, and the production cycle is lengthened. Therefore, if possible, the aluminum-lined substrate is not used as much as possible. The substrate of the board.

As the ROGERS company's TMM series of microwave printed board substrate, is composed of ceramic powder filled thermosetting resin. Among them, the TMM10 substrate filled with more ceramic powder, the performance of the more brittle, to the graphics manufacturing and shape processing process is very difficult, easy to defect or the formation of internal cracks, the relatively low yield. At present, the method of laser cutting is used for the profile processing of the TMM10 plate, which has high cost, low efficiency and long production period. Therefore, where possible, consideration may be given to selecting RT/Duroid series substrate boards that ROGERS meets the corresponding dielectric properties.