At present, most Halogen Free PCB material are mainly phosphorus-based and phosphorus-nitrogen-based materials. When the phosphorus-containing resin is burned, it is decomposed by heat to generate metaphosphoric acid, which is extremely dehydrated, so that a carbonized film is formed on the surface of the polymer resin, and the burning surface of the resin is isolated from the air, so that the fire is extinguished and the flame retardant effect is achieved. Polymer resins containing phosphorus and nitrogen compounds produce incombustible gas when burning, which helps the resin system to be flame retardant.

1.Etching

Because of the poor fluidity of halogen-free epoxy resin and the poor interpenetrating ability of copper foil interface, the peeling strength of copper foil of Halogen Free PCB is poor. Compared with conventional materials, halogen-free materials increase the pressing pressure in the pressing process in order to enhance the binding force between copper foil and resin, which leads to the deeper depth of part of copper embedded in the resin, which easily leads to the phenomenon of etching uncleanness in the etching process (the copper is exposed in the stars). In order to solve this problem, it is often improved by increasing the amount of wire width on the working negative and properly adjusting the etching rate.

2. Lamination

The content of nitrogen and phosphorus is higher than that of halogen in conventional halogen-based flame retardant materials, which leads to the increase of polymerization degree and molecular weight of polymer. Therefore, the molecular chain movement of halogen-free epoxy resin after heating is slower than that of conventional materials, which shows that the fluidity of halogen-free materials will be lower than that of conventional epoxy resin under the same conditions.

3. Drilling electroplating

Halogen Free PCB material have higher Young's modulus, which increases the rigidity and brittleness of materials, because of the use of P and N series functional groups to increase the molecular weight and the rigidity of molecular bonds. At the same time, the TG point of halogen Free PCB material is higher than that of conventional materials of the same type. Therefore, it is necessary to properly increase the rotation speed of the drill and reduce the feed speed of the drill to ensure the roughness of the hole wall when mechanical drilling is carried out. In the process of horizontal deslagging, it is necessary to prolong the expansion reaction time, increase the roughness of the hole wall and improve the bonding force between electroplated copper and the hole wall according to the characteristics of halogen-free materials.

4. Laser drilling

Comparing halogen-free materials with conventional materials under the same technological conditions of laser drilling, it is found that the hole wall roughness and verticality of halogen-free materials after drilling are not as good as those of conventional materials, which can be more prominent after electroplating. Therefore, it is necessary to appropriately increase the pulse energy and quantity of laser drilling of Halogen Free PCB material.

5. Solder resist fabrication

Halogen-free solder resist ink has a high solid content of curing agent (take Company C as an example: conventional halogen-free material is 15% and 30%), so its viscosity is high and fluidity is low. In printing, it is necessary to increase the pressure of scraper and adjust the mesh number of screen. Under certain conditions, a certain amount of diluting solvent can be used for dilution to increase the fluidity of ink.

6. Impedance fabrication

At low frequency (less than or equal to 1.5GHZ), the dielectric constants of the two materials are less affected by thermal shock and decrease to some extent. When the test frequency reaches a certain value (1.8GHZ), the two materials are obviously different under the influence of thermal shock. The dielectric constant of halogen-free materials decreases obviously and fluctuates slightly after thermal shock, while the dielectric constant of conventional materials increases greatly with the increase of thermal shock times.
Therefore, halogen-free materials can avoid the influence of multiple thermal shocks on the dielectric constant of the materials in the PCB process, which is beneficial to the control of characteristics or differential impedance. Halogen Free PCB material have higher dielectric constant, and the dielectric thickness after lamination is thicker than that of conventional materials, so the impedance value will be increased to a certain extent when impedance control, especially the control of characteristics and differential impedance. When designing the wire width, appropriate compensation is needed.