(1) The PIM value is affected by the current density and is related to the designed circuit. The smaller the current density, the better the PIM performance.

　　(2) The rougher the surface of the copper foil, the worse the PIM performance. On the contrary, the smoother the surface of the copper foil, the better the PIM performance.

　　(3) The surface treatment of solder mask oil and chemical tin can optimize the PIM, which is about 4-6dBc. However, the thickness of chemical tin has almost no effect on the PIM value, and the PIM performance of chemical nickel gold is poor.

　　(4) Material structure, try to avoid impedance discontinuity, keep consistent impedance characteristics as much as possible, and choose low PIM materials (such as PTFE or PI materials).

　　(5) The influence of dielectric layer thickness on PIM needs further verification.

　　(6) The smaller the copper thickness, the better the intermodulation performance. This is because the thicker the copper thickness, the worse the etching effect, and the etching burrs will affect the intermodulation performance.

　　(7) The burr/etch factor of the line etching, the etching factor control is ≧3.0, the smaller the burr, the better the PIM performance. Micro-etching process is recommended for the pre-treatment of solder mask.

　　(8) Surface ink thickness, the thicker the ink, the better the PIM performance.

　　(9) The surface of the coating is oxidized, the conductivity is not good, and the thickness of the coating is not enough.

　　 (10) contains magnetic materials such as iron, cobalt, nickel, etc.

　　(11) Temperature coefficient of dielectric constant (TCDk, used to measure the change of Dk with temperature), the lower the better.

　　(12) The wire length from 254mm-76.2mm is the common specification for material loss performance, the wire length is 254mm, 127mm, 76.2mm. The longer the line, the worse the intermodulation value.

　　(13) The line width is reduced from 2.0mm in diameter to 0.25mm, and the influence of the difference of standing waves on the intermodulation can be investigated. The line width is narrowed, the impedance increases, and the reflected energy also increases. The superposition of the reflected energy and the incident energy causes the energy to converge, leading to the temperature rise of the line under test. The intermodulation value is inversely proportional to the temperature, and the narrowing of the line width causes the temperature to rise, and the intermodulation becomes worse.

　　 (14) The PCB level should introduce grounding on both sides of the microstrip line of the RF board. Don't just choose a line without choosing the top ground. The test results show that the top ground will improve some PIM.

　　(15) If capacitors are needed for the microstrip line in the board, try to use a small Q value, and the frequency selection effect should be slightly better.