Microwave Tech - Certain materials in high-frequency laminates have different effects on the process

This article mainly discusses the type of circuit process route. High-speed PCB circuit designers tend to use high-frequency laminates with low insertion loss and satisfactory impedance control advantages, but these materials will affect the circuit process.

The circuit technology of the high-frequency laminate is more complicated.

This is mainly due to the different materials in the high-frequency laminates. Some materials and other materials in the high-frequency laminates have different effects on the process.

Another view is that these individual materials have a mixed structure, which means that dissimilar materials are joined to each other in the PCB.

Generally speaking, there are three types of high-frequency laminate materials: hydrocarbon natural resin overall system, PTFE overall system, and PTFE filler overall system.

In the overall system of these individual products, it is divided into substrates containing glass cloth and non-glass cloth. The overall system material of polytetrafluoroethylene filler depends on different filler components to obtain special specified electrical properties.

The bonding of all materials and fillers will affect the process of the PCB board. The main filler of the overall system material of hydrocarbon natural resin is ceramic powder. Variety of types of ceramic filler will change the properties of the material.

When choosing a filler, it is necessary to consider the electrical properties and thermal characteristics of the problem. Porcelain filler is often used to change the dielectric constant of the material and increase the degree of reinforcement. Many ceramic fillers can adjust the thermal expansion coefficient of the material to make it closer to the performance of copper.

Some ceramic fillers will more or less affect PCB drilling and processing. Under the use of ceramic filler hydrocarbon materials, the filler will affect the life of PCB etching lines and drilling tools. In addition, the type of PCB processing tools is also more critical.

For example, the recommended processing tool for the natural hydrocarbon resin RO4350B, which is high-frequency, reinforced with glass cloth, and filled with ceramic filler, is a carbon steel spiral planer or a diamond cutting tool.

The recommended form of processing is deemed appropriate and the method of etching copper foil is used. Some commonly used processing parameters are shown in Figure 1.

Figure 1: Common processing parameters of high-frequency laminates

These referral programs are generally used in PCB processing plants, and the material suppliers should provide PCB processing conditions.

Hydrocarbon materials without glass cloth and ceramic fillers are mainly used for economic activities. This material is fragile and easily broken during PCB processing. The routing of the PCB board is not the focus during the processing.

Because of the addition of ceramic fillers, materials with different dielectric constants have different wear parameters. Materials with low dielectric constant (dielectric constant less than 4) are less delicate, which reduces the lifetime of the tool.

In addition, the non-exquisite and special nature of the material will affect the quality of the edge of the line, such as burrs. Once again emphatically pointed out that all of a sudden, material suppliers should provide PCB processing plants with the best processing conditions.

The high-frequency substrate made of polytetrafluoroethylene and the hydrocarbon material of the ceramic filler have different concerns.

Polytetrafluoroethylene materials are relatively soft and are prone to stains and scratches during processing. This requires a different process to reduce such phenomena.

The use of slower surface speed processing that is deemed appropriate can reduce the heat consumption and the standard double-pass drilling pattern that occurs during processing. This two-way standard pattern spreads upwards in two directions, one is counterclockwise and the other is clockwise.

PTFE materials with ceramic fillers are easier to process than pure PTFE materials. Adding ceramic fillers increases the hardness of the material and increases the thermal conductivity.

The increase in thermal conductivity reduces the overheating of the substrate, and overheating is the cause of stains in the process. Sometimes glass cloth is added to this material, but the processing technology is similar.

Materials including glass cloth can increase the quality of edge cutting. Regardless of whether it is processing reinforced or non-reinforced PTFE materials, attention should be paid to reducing residues, and it is recommended to use the back plate to design the vacuum channel form when it is deemed appropriate during processing.

Mixed PCB materials become more and more widespread. The use of different materials to press the multilayer board has many advantages, but there are many process problems.

Different materials have different special properties in the plate shape, and there are process problems on the contact surface between the materials. Basically, the main problem is the transition from soft materials to hard materials, and the processing technology is more complicated.

Soft materials require ductility, while hard materials have advantages in cutting. Different materials are used in the circuit stack to generate local transition challenges due to the difference in thickness.

In short, the process parameters should be mainly inclined to the processing needs of soft materials, and the material supplier should provide the PCB processing factory with the help of optimizing the process