PCB Material List - Rogers TMM series high frequency PCB material processing reference

ROGERS has launched a unique solution, low-dielectric constant thermal change rate high-frequency PCB - TMM microwave PCB material series. TMM thermosetting microwave PCB material is a ceramic filled thermosetting polymer, specially designed for stripline and microstrip line applications that require high through-hole reliability.

Rogers TMM microwave microwave PCB material can mature using traditional cemented carbide tools for forming processing. Using proper methods and tools, it can have a useful life of more than 250 linear inches during machining. For materials with low dielectric constant, the lifetime is slightly lower. This article discusses the factors that affect tool wear and edge quality. The reference table provides various tool sizes and Rogers TMM grades recommended molding conditions and life estimates of various tools.

The Rogers TMM microwave PCB material is composed of hydrocarbon polymers that are highly filled with ceramic fillers. This provides Rogers TMM microwave PCB material with low thermal expansion and a variety of dielectric constants.

Due to the abrasiveness of ceramic fillers, preventive measures are required during molding. Avoid excessively high surface speeds (>400SFM) to prevent excessive tool wear and reduced edge quality.

The following machining recommendations are based on tests done on Excellon EX drilling/milling machines. Several cemented carbide tools have been evaluated within a certain range.

Surface speed and cutting load

The surface speed is defined as the peripheral cutting speed of the tool. The following formula can be used to calculate the spindle speed under the specified tool diameter and surface speed.

Spindle speed=12*surface speed (feet/min)/unit*tool diameter

Cutting load is defined as the distance the tool travels per revolution. The following formula can be used to calculate the feed under the specified cutting load and spindle speed.

Feed amount = cutting load * spindle speed

Recommended Rogers TMM milling conditions and tool life

Based on quality control considerations such as copper foil burrs, negative groove widths, rough sidewalls and final tool life, the final tool life provides a good quantitative basis for comparing tool shapes and milling conditions. However, due to the need for edge quality, the useful tool life value will be significantly reduced. Useful tool life estimates are generally only 50% to 60% of the final tool life. For demanding applications, tools need to be replaced more frequently.

Factors affecting tool life:

Various factors can affect the useful life value of the tool when machining Rogers TMM monolithic or laminate. They include Rogers TMM grade, surface speed, tool shape, cutting load, tool size and stack thickness.

Rogers TMM grade:

Rogers TMM materials with lower dielectric constants contain more high-viscosity fillers. Therefore, the tool life when machining Rogers TMM3 is shorter than when machining Rogers TMM10. Under proper processing conditions and using the correct tool, the useful life of Rogers TMM3 is approximately 120 linear inches, while Rogers TMM10 can exceed 250 linear inches.

Tool surface speed:

The effect of surface speed on the final tool life. The Rogers TMM3 is processed by tools of various geometric shapes. The final tool life decreases with the increase of surface speed. The spindle speed ranges from 15KRPM to 25KRPM (3/32 inch)

Tool geometry:

Among the tools of various geometric shapes to be evaluated. For practical considerations, this study only includes tools from three suppliers. However, tools with similar geometries should have similar test results from other suppliers.

Generally speaking, a tool with a larger number of blades has an excellent tool life. The geometry of Precision Carbide R1U, R1D and MegaTool RCS tools provide the best final tool life. These tools are usually used for milling traditional PWB materials, such as FR4. Tools commonly used for milling the geometry of PTFE laminates, such as the Presicion Carbide EM2 tool, have a short final tool life due to its relatively small cross-sectional area.

Feed (cutting load)

The effect of cutting load on the final tool life of various shapes of tools is shown in Table 2. When the cutting load increases, the final tool life decreases. However, too small cutting loads (<0.001 inch/revolution) should be avoided, which will cause obvious copper burrs.

Tool size

Due to the increase in tool cross-sectional area, larger tools generally have better final tool life at a given surface speed. Therefore, smaller tools usually need to be replaced more frequently.

Stack thickness

The final tool life also decreases as the thickness of the stack increases. This is due to the increased radial pressure on the tool. As the thickness of the stack increases, the tools should be replaced more frequently.

TMM microwave PCB material series are ceramic-filled thermosetting resin polymer materials, which are mainly used in high-reliability microstrip lines and strip lines. The TMM series substrate multilayer board has a low TCEr (dielectric constant change with temperature), a thermal expansion coefficient matching copper, and the most stable dielectric constant in the industry. These characteristics make TMM materials an ideal choice for many applications.

In order to meet the needs of TMM materials in stripline applications, we evaluated the following adhesive sheets available in the market.

DuPont FEP model C20 (adhesive on both sides)

Rogers 3001 CTFE film

Dupont FEP Model A

However, the above bonding sheets are all materials with low dielectric constant, which will reduce the dielectric constant of the entire microstrip line structure. This effect of the adhesive sheet will vary based on the circuit design, material type and thickness. So it needs to be evaluated according to each practical application.

Two materials, TMM-3 and TMM-10, were selected and evaluated with all the above adhesive sheets respectively. Before pressing, the copper foil of all TMM sheets will be etched away and baked at 110°C/1 hour. The TMM sheet does not need to be etched with sodium metal to activate the surface of the medium like the glass cloth reinforced PTFE sheet. Used in the evaluation is a 2mil thick adhesive sheet, which is pressed together with a 6-inch X 6-inch flat press. Before pressing, heat the flat press to 300°C (PEF as the bonding sheet) and 220︒C (3001 as the bonding sheet), and then put the laminated multi-layer board into the press for pressing. Maintain a pressure of 200PSI throughout the process and keep it at the above temperature for 20 minutes. The samples were layered into three groups, and the peeling test was done after treatment under different conditions.

Product processing conditions:

1. Condition A: No processing will be done.

2. Thermal shock: bleaching tin at 288°C /10 seconds

3. Temperature/Humidity: Place in a 17PSI pressure cooker for 2 hours

The test results show that FEP C20 pressed samples have the best test results in all test environments and conditions. Rogers 3001 performs well after pressing and after thermal shock, but it is not recommended to be used in environments with temperature and humidity requirements in. However, FEP-A has insufficient binding force under all test conditions, so it is not recommended to use it.

Note:

1. When drilling the TMM multilayer board, the drill pin wears out very quickly, which may cause excessive drilling dirt on the soft fluoropolymer bonding layer. The number of holes of the drill pin needs to be determined according to the thickness of the substrate, the design requirements, and the quality of the observation hole wall.

2. Although TMM material does not require sodium etching before electroplating through holes, it is necessary to use sodium etching after TMM and FEP C20 or 3001 are pressed together. Because if this treatment is not done, the bonding force between the bonding sheet layer and the chemical copper is poor, thus forming a risk point on the hole wall.

3. The high-frequency plates of all hydrocarbon resin systems including R04000 or TMM, exposed to an aerobic environment for a long time, may cause changes in the electrical properties of the materials. These changes will intensify as the temperature increases. Whether these changes occur and whether they will affect the performance of the final product depends on various complex factors, such as circuit design, performance tolerances, working conditions, and the unique use environment of various products. Although Rogers has been committed to developing improved antioxidants to reduce the oxidation of RO4000 and TMM. Rogers always advises circuit design engineers/end users to determine whether the material is suitable for the entire life cycle of the product by testing performance and indicators in each application.