PCB Laminate is an essential component as it holds the different layers of a PCB together. Traditionally, a PCB has multiple layers of substrate, copper, solder mask, and silkscreen. These layers are sandwiched between the laminate sheets that are then heated and pressurized to create the final piece of uniform thickness; the process is called lamination.

There is various material available for lamination like FR-4, Polyimide, Teflon etc. It is essential to choose the appropriate material for lamination as it forms the base for the PCB. The selection of appropriate material is a technical process as it requires due consideration of the thermal, electrical, chemical and mechanical properties of the material.

Do consider the following points while selecting application-centric PCB laminate material:

Mechanical Properties:

• High Peel Strength for lesser chances of de-lamination. The peel strength is the bonding force between the lamination and the copper layers.
• High Flexural Strength to avoid any cracks or breaks. Flexural strength is the ability of the material to withstand physical stress without causing any cracks or damage to the material.
• Delayed De-Lamination Time for higher durability. The delamination time defines the duration, a PCB laminate can withstand exposure to high temperatures before it starts to unravel. 

Thermal Properties:

• Optimal Glass Transition Temperature (Tg). The glass transition temperature defines the sensitive temperature range of the substrate, exposure to which can cause the substrate to harden or soften.
• Lower Thermal Expansion to avoid any changes in the dimension or other stress on the PCB. This is possible if the substrate has higher CTE i.e. Coefficient of Thermal Expansion. CTE is the expansion rate of a PCB.
• Higher Thermal Conductivity (k) to allow adequate heat distribution. It is directly linked to the heat transfer capability of the board. A lower k may result in uneven distribution of heat across the board which might result in overheating of certain layers.
• Higher Decomposition Temperature (Td). If exposed to a higher temperature, the substrate starts to decompose, which needs to be avoided in any case. It is essential to ensure that the Td of the material is higher than that of the board.

Chemical Properties:

• Non-Flammable Material. When exposed to heat, if the material is combustible, there are chances of the circuit board catching fire. 
• Moisture Absorption Value of Substrate ranging from 0.01% to 0.20%. The moisture absorption value directly affects the substrate’s thermal and electrical properties. It also increases the rate of delamination, making it water-resistant.

Electrical Properties:

• Dielectric Constant (Er) ranging between 3.5 to 5.5 Er. The electrical resistance and signal integrity of the substrate defines the Er. The dielectric constant and dielectric loss tangent of the material needs to be maintained at a stable range to avoid electric shocks.
• Dielectric Loss Tangent ranging between 0.02 to 0.001 to not let the material lose its strength. Though, one must be very careful of the Loss tangent in the case of analogue signals. 
• Higher Electrical Strength ranging between 800V/mil to 1500V/mil to withstand any electrical breakdown.
• Also, one must ensure the optimal Volume Resistivity (p) and Surface Resistivity (pS) of the substrate.

The above-mentioned properties play a crucial role in defining the efficiency of your circuit board. The safety and smooth functioning of your electric device is major concern, and one must never ignore that. Only seek a trusted name like Gelco when it comes to electric solutions like these.