PCB Base Materials


June 2, 2020

Selecting the surface finish and getting the design optimised are important steps in ensuring that your product performs well, but is that the end of the process? No, you also have to ensure that the material specified is available within the factory and that the factory is UL approved to support such materials.

LHD knows that there are many options concerning base materials and with our technical knowledge we can help guide and assist you in terms of material selection and material specifications.

Rigid material

How should material be specified?

Our recommendation is not to specify one specific brand or type of material wherever possible, as this can ultimately limit the supply chain options in terms of who can support the project. The reason for this is that whilst there are many well known brands of material widely in use within our factory base, there are occasions where some factories have several material brands or preferences which achieve the required material specification. Availability and indeed price can then become factor as to which brand will be used.

This does not mean that you cannot specify known materials, far from it. If you have experience of a material which you know works for your product, then it can simply be referenced with a comment stating “or equivalent” and LHD’s technicians and procurement teams can review and offer you an alternative that will meet the functional needs without compromising performance.

Every well-known manufacturer of material will have their product categorized in accordance with IPC 4101 (specification for base materials for rigid and multilayer printed boards) with the aim of this specification being to identify and categorise performance characteristics. Using this categorisation approach is ideal as it defines the characteristics of the base material, in detail, and allowing the factory to follow the IPC-4101-xxx categorisation enables them to select wisely thus ensuring performance is nothing less than expected.

If you you wold like more information on IPC 4101 or material specification methods, then please contact LHD Technology who will be happy to help.

Key factors in specifying material characteristics

When considering the performance characteristics of the base material, consideration should be given to both the mechanical properties (specifically in relation to how the material shall perform during heat cycling / soldering operations) and also the electrical properties associated with the material. These are typically regarded as the most common factors for selection of standard products. This comment is based upon all material being considered able to meet UL flammability rating V”0.

Key material characteristics

“CTE – Z axis(Co-efficient of thermal expansion): This is a measure of how much the base material will expand when heated. Measured as PPM/degree C (both before and after Tg) and also in % over a temperature range.

Td (Decomposition temperature): This is the temperature at which material weight changes by 5%. This parameter determines the thermal survivability of the material.

Tg (Glass transition temperature): The temperature at which the material stops acting like a rigid material and begins to behave like a plastic / softer.

T260 (Time to delamination): This is the time it take for the base material to delaminate when subjected to a temperature of 260 degrees C.

T288 (Time to delamination): This is the time it take for the base material to delaminate when subjected to a temperature of 288 degrees C.

Dk (Dielectric constant): The ratio of the capacitance using that material as a dielectric, compared to a similar capacitor which has a vacuum as its dielectric.

CTI (Comparative tracking Index): A measure of the electrical breakdown properties of an insulating material. It is used for electrical safety assessment of electrical apparatus.




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