Copper laminates are very frequently used clads (of copper spread) over the resin composite materials for the PCB manufacturing industry. The copper is a good conductor that provides conductivity and resin is a composite insulator material which is hard and stiff. This is also called a base material for PCBs manufacturing. The base material can be either a rigid or flexible in nature. The very fundamental purpose of a copper laminate in an electronics product is to mechanically support and electrically interconnect the pins i.e., provide firm base to hold the electronic components and simultaneously electrically join them.
The most widely used resins in the electronics industry are polyimide, cyanate ester, polyester, phenolic and epoxies. The epoxy, phenolic and polyimide have more than 90 percent consumption in PCB market. The resin material selection accounts for thermal, chemical, mechanical and electrical characteristics. The dominant characteristics of raw resin material determine the best suitable application of the PCB.
Following are the popular copper laminate types used for PCB manufacturing:
Polyimide: It is used for high temperature PCB applications and provides more rework cycles for soldering and desoldering of components. It’s Tg, glass transition temperature, is 220°C so provides very good performance over high temperatures.
FR-4: FR-4 is a fiberglass resin based base material. It is a strong, fire retardant, hard to cut and hard to bend material. It’s Tg is around 160°C. There are various versions of the FR-4 material. It is used in single, double and multilayer PCBs of digital, analog, mixed-signal and power supply applications.
Phenolic: Phenolic base material is used in low cost applications available with the FR-2, CEM-1 or CEM-3 brand names. It is most widely used in single layer PCB of small household gadgets and appliances. It is slightly brittle but hard to bend.
Arlon: Arlon materials have different variants and their typical applications do starts beyond the application of FR-4 materials. It is a base material as well as the prepreg material for the multilayer PCBs. Their major applications are military, avionics, wireless, semiconductor test and communications systems.
Other copper clads laminates used are Tetrafunctional epoxy, Thermount and cyanate ester etc.
For electrically interconnecting the components the laminates can be made of nickel, stainless steel, aluminum, beryllium and copper. However, the most widely used material for lamination purposes is copper. The aluminum found commercial applications recently and is appreciated in low cost home appliances. The conductive cladding layer is very thin and is over one or both sides of the resin composite material. The thickness of the cladding material is determined that how much material is deposited in terms of weight. Common weights of the copper layer are 3/8, ½, 1 and 2 ounce per square inches correspondingly their thicknesses are 12, 18, 35 and 70µm respectively.
Fig. 1:- PCB laminated basic structure
Fig. 2:- PCB copper clad sheet for copper laminates
Fig. 2:- Multilayer PCB manufacturing using rigid and flexible copper laminates
For multilayer PCBs the multiple different layers are manufactured and then stacked as per deign. The two conductive layers are separated by prepreg materials and then pressed, to make tem stiff and stick together, under specified controlled temperature and pressure.