by Ava
October 8, 2022
PCB knowledge
(0)
06 mins

PCB laminate – the significant part for PCB

What is PCB laminate

PCB manufacturers use laminates to fabricate PCBs. PCB laminates are generally, number of layers that are bounded together thermally and also by applying pressure. PCB laminate is usually considered a binding force to hold layers of PCB together.

The laminates are created by processing fabric under pressure and at high temperatures with thermoset resin to generate a final product of consistent thickness. Different parameters like dielectric properties and flammability are affected by varying physical parameters of PCB laminate.

What is PCB laminate used for?

The building block of any PCB is “Laminate” . PCB laminate plays a pivotal role in determining the whole PCB performance. In order to fabricate multilayer PCBs, different materials are used by PCB manufacturers to manufacture different kinds of laminates, which will be then used to fabricate PCBs according to different environmental conditions in which that particular PCB has to operate.

These laminates describe the overall properties of PCB like the mechanical and electrical properties or thermal conductivity. Due to this reason, it is important to choose the perfect material for laminates, according to the environment in which PCB has to operate.

What are the properties of laminate?

Properties of PCB laminate are classified into the following four categories

Mechanical Properties

As there are possibilities that PCB might pass through severe stressful environmental conditions during its lifespan. So, PCB laminate must sustain that harsh environmental conditions in order to perform without any fault. Mechanical Properties are further categorized into the following types

Peel Strength: It is the strength between different layers of PCB laminate.
Flexural Strength: It represents the flexibility of laminate i-e the ability to bend without
breaking or having cracks.
Delamination Time: The time required for PCB laminate to delaminate under severe
environmental conditions. More delaminate time means higher durability.

Chemical Properties

Chemical properties of PCB laminate also plays important role in the durability ofPCB and are divided into the following categories.

Flame Resistance: This quality provides strength to resist the effects of flames when PCB is exposed to it.
Moisture Absorption: PCB laminate with more moisture absorption ability results in quick delamination of PCB.
Methyl Chlorine Resistance: If Methyl Chlorine resistance is high in PCB laminate then this means it has more chemical absorption ability.

Electrical Properties

Following types of electrical properties of PCB Laminate are important to consider

Dielectric Properties: Dielectric loss tangent and Dielectric Constant are important as if these factors are kept controlled within the correct range then it prevents electric shock.
Insulating Properties: It defines resistivity measures and prevents PCB from the sudden electric flow.
Electric Strength: This property provides strength against the electrical breakdown of the material.

Thermal Properties

Following are some properties of PCB laminate under this consideration

Glass Transition Temperature: If PCB laminate changes its texture and physical composition, i-e hard to soft or vice versa, with respect to temperature then this property is known as Glass Transition Temperature.
Thermal expansion: Properties related to contraction and expansion at different temperature ranges. Generally with low-temperature expansion laminates are chosen in order to reduce dimensional changes caused by thermal exposure.
Thermal Conductivity: it is related to the conductivity of heat through the laminate,generally with higher thermal conductivity laminates are chosen for PCBs.

What constituents is PCB laminate made of？

Following are the seven different constituents used to make PCB laminate

Support material: material used to provide support mechanically and also give electrical properties to laminate, for example, woven glass.
Coupling Agent: provides binding force among inorganic glass and organic resin. Stiffener: sometimes also known as Matrix, used as a binding force and also transferring the load. Usually provides tensile strength along with thermal stability.
Curing Agent: used to improve polymerization in the organic resin. It enhances impact an also compact strength and makes laminate tougher.
Flame Retardant: This material is used to enhance the thermal abilities of PCB Fillers: The main purpose of fillers is to reduce thermal expansion and dissipation by filling emptied spaces.
Accelerators: As the name suggests this material is used as a catalyst to enhance the reaction rate.

What are the main types of laminate material ?

Following are the main types of PCB laminate material.

FR-4: This type of PCB laminate is most frequently used for SMD assembly. This materialis flame-resistant and has more strength to weight ratio.
High Tg Epoxy: This type of laminate has an extreme level of chemical resistance and good thermal performance. PCBs made up of this material are good electrical insulator and are economical and offers fire resistance. Due to all these characteristics, such laminates are suitable for multi-layer PCBs.
BT Epoxy: Because of its superior mechanical, thermal, and electrical qualities, BT epoxy is frequently used. This laminate may be used to make lead-free PCBs. It is most commonly employed in multilayer PCBs. It has enough strength to keep its binding force even at high temperatures.
Polyimide: This type of laminate exhibits circuit trace bonding strength and severe

environmental resilience. Due to its exceptional chemical, thermal, and mechanical qualities, these are suitable for military equipment, automotive, and consumer electronics sectors.

Is laminate same as the core of PCB?

PCB laminate and PCB core might be similar in some cases or can be categorized as different. PCB core comprises of a single laminate layer or multiple layers of laminate which are stacked up, then pressed, cured thermally, and plated with copper on both sides. While PCB laminate can be considered as a binding force that bound all core materials together. In some cases, the dielectric constant may be different of both PCB core and PCB laminate.

How to choose PCB laminate for fabrication?

It is very important to select the right laminate type for PCB by taking into consideration about applications of PCB and under which conditions the PCB might be in operational mode in order to enhance PCB lifespan and improve the operational performance of PCB. The following factors should be kept in mind while selecting the perfect laminate for PCB.

Dielectric Constant
Thermal Conductivity
Transition Temperature
Coefficient of thermal expansion
Loss factor
Electrical performance

Which laminate is used for making flexible PCB?

Among all types of PCB laminates, Polyimide is the one that is used commonly for fabricating flexible PCBs. This is because of its chemical, thermal, electrical, and mechanical characteristics. The main reason behind using this material for fabricating flexible PCBs is because this offers extensive tensile strength due to which PCBs made of this material, are exceptionally flexible.

What is the difference between laminate and prepreg?

PCB laminate is over-cured sheets that are pre-impregnated with resin, while prepreg is a type of fiber-glass that is impregnated from resin and then vacuum bagged. PCB laminate is the conventional way to fabricate PCBs while prepreg is a relatively newer technology and best suited for fabricating high-density PCBs.

Both PCB laminates and prepreg have their own pros and cons, like, PCB laminates are cheaper but not stronger than prepregs. In short, laminates are used in the fabrication of low-density PCBs while prepregs are used to fabricate high-density PCBs.

Conclusion

PCBs are building blocks of electronic appliances, so it is important to know which type of material should be used to fabricate PCBs.

The procedure to follow while selecting a specific laminate for PCB is to check under which environmental conditions,PCB have to operate and after a thorough analysis specific material for laminate should be selected for fabrication of PCB.

PCB laminates also define the specifications of PCBA to be formed and has large impact on PCBA reliability and durability.