pcb prototype fabrication-Introduction of Copper Clad Laminate

What is Copper Clad Laminate?

Copper Clad Laminate, abbreviated to CCL, is a type of base material of PCBs. With glass fiber or wood pulp paper as reinforcing material, a CCL is a type of product through lamination with copper clad on either one side or both sides of reinforcing material after being soaked in resin.

How are CCLs Classified?

According to different classification standards, CCLs can be classified into various categories:

• Based on CCL mechanical rigidity, we have rigid CCL (FR-4, CEM-1, etc.) and flex CCL. Rigid PCBs depend on rigid CCLs while flex PCBs are on flex CCLs (flex-rigid PCBs are on both rigid CCLs and flex CCLs).
• Based on insulation material and structures, we have organic resin CCL (FR-4, CEM-3, etc.), metal-base CCL, ceramic-base CCL etc.
• Based on CCL thickness, we have standard thickness CCL and thin CCL. The former one requires at least 0.5mm thickness while the latter can be thinner than 0.5mm. Copper foil thickness is excluded from CCL thickness.
• Based on reinforcing material types, we have glass fiber cloth base CCL (FR-4, FR-5), paper base CCL (XPC), compound CCL (CEM-1, CEM-3).
• Based on applied insulation resin, we have epoxy resin CCL (FR-4, CEM-3) and Phenolic CCL (FR-1, XPC).

What Makes an Excellent CCL?

CCLs only perform well when catering to performance requirements in the following aspects:

• Appearance. Issues may be caused on copper foil due to unexpected elements in manufacturing process such as dent, scratch, resin point, wrinkle, pinhole, bubble etc. All those problems will definitely lead to low performance of CCL and then PCB. Therefore, an excellent CCL should be flat and smooth in appearance.
• Size. Since CCLs are base material of printed circuit boards, they have to conform to size requirements corresponding to PCBs. Parameters concerning the size of CCLs include length, width, diagonal deviation and warpage, each of which has to meet specific requirement.
• Electric performance. This is an essential mission for a PCB prototype fabrication so any aspect affecting its electric performance has to be carefully designed including dielectric constant (Dk), dielectric loss tangent (Df), volume resistance, surface resistance, insulation resistance, arc resistance, dielectric breakdown voltage, electric strength, Comparative Tracking Index (CTI) etc.
• Physical performance. Parameters concerning physical performance of a CCL include dimensional stability, peel strength (PS), bending strength, heat resistance (including thermal stress, Td, T260, T288, T300), punching quality etc.
• Chemical performance. Chemical performance of a CCL has to meet the requirements of flammability, chemical reagents resistance, Tg, Z-axis coefficient of thermal expansion (Z-CTE), dimensional stability etc.
• Environmental performance. It has to cater to the requirements in terms of water absorption etc.

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