PCB substrate selection

The first considerations for selecting substrates are temperature (welding and working), electrical properties, interconnects (welding elements, connectors), structural strength and circuit density, etc., followed by material and processing costs. Please refer to the following figure for details:

▲ Substrate selection diagram (source: source “GJB 4057-2000 Printed Circuit Board Design Requirements for Military electronic Equipment”)

Noun explanation

FR-4

Fr-4 is a flame resistant material class code, which represents the meaning of the resin material after the combustion state must be able to self-extinguish a material specification, it is not a material name, but a material class.

Tg/ glass conversion temperature

Tg value refers to the temperature at which the material changes from the more rigid glass state to the more elastic and flexible rubber state. Note that material properties change above Tg.

CTI

CTI: Comparative Tracking Index, abbreviation of Comparative Tracking Index.

Meaning: it is the indicator of leakage resistance. In the state of applying voltage to the surface of the insulating material, make the electrolytic droplets fall on the surface of the molded product between the electrodes, and evaluate the voltage until no leakage damage.

CTI level: the CTI level ranges from 0 to 5. The smaller the number, the higher the leakage resistance.

PI

Polyimide (PI) is one of the organic polymer materials with the best comprehensive performance.Its high temperature resistance up to 400℃ above, long-term use temperature range of -200 ~ 300℃, part of no obvious melting point, high insulation performance, 103 hz dielectric constant 4.0, dielectric loss only 0.004 ~ 0.007, belonging to F to H.

CE

(1) CE cyanate resin is a new type of electronic material and insulating material, which is one of the important basic materials in the field of electronic appliances and microwave communication technology. It is an ideal resin matrix material for radome. Because of its good thermal stability and heat resistance, low linear expansion coefficient and other advantages, CE resin has become an excellent matrix material for the production of high frequency, high performance, high quality electronic printed circuit boards; In addition, CE resin is a good chip packaging material.

(2) CE resin can be used for the production of military, aviation, aerospace, navigation structural parts, such as wings, ship shells, etc., but also can be made into aerospace foam sandwich structural materials commonly used.

(3) CE resin has good compatibility, and epoxy resin, unsaturated polyester and other copolymerization can improve the heat resistance and mechanical properties of the material, can also be used to modify other resins, used as adhesives, coatings, composite foam plastics, artificial media materials, etc.

(4) CE is a good transmittance material with high transmittance and good transparency.

PTFE

Poly Tetra fluoroethylene (PTFE), commonly known as “non-stick coating” or “easy to clean material”. This material has the characteristics of acid and alkali resistance, resistance to various organic solvents and high temperature.

High temperature resistance: long-term use temperature of 200~260 degrees;

Low temperature resistance: still soft at -100 degrees;

Corrosion resistance: able to aqua regia and all organic solvents;

Weather resistance: the best aging life of plastics;

High lubrication: the lowest friction coefficient of plastics (0.04);

Nonviscous: having the smallest surface tension of a solid material without adhering to any substance;

Non-toxic: physically inert; Excellent electrical performance, is the ideal C class insulation material, a thick layer of newspaper can block 1500V high voltage; It’s smoother than ice.

Whether it is ordinary PCB design, or high-frequency, high-speed PCB design, the choice of substrate is an essential knowledge, we need to master. (Integrated PCB).