How to Choose PCB Assembly Material?

Different materials are there in the market to make printed circuit boards. The basic purpose of a PCB is to provide electricity to run electronics, besides, it helps insulate the copper layers. Though some PCB assembly materials are common like FR4, and Teflon, the nature and type of a PCB determines a suitable material for it. When choosing a material for circuit boards, you have to see their properties in terms of thermal, chemical, electrical, and mechanical properties. Let’s study these properties in detail and material types.

There are six basic components of the standard PCB board and these are:
• Prepreg
• Laminate
• Copper foil
• Soldermask
• Nomenclature
• Final finish

Copper-clad laminates are particularly composed of the prepreg sheets and these were laminated together with the pressure and heat. These were with copper foil sheets on either end and as the resin hardened, PCB resulted in laminating like a plastic composite provided with the copper foil sheets on both ends.

There is also a solder mask that specifically protects the PCB outer layers and these are required for the protection of the exposed copper holes and pads which are typically planned for soldering and mounting the components. For protecting the areas and providing a decent solder-able finish, this usually links with making usage of the metallic coatings including nickel and other finishes designed for the PCB manufacturer.

Electrical Properties of A PCB Material

A PCB material’s electrical properties include the Er relative permittivity or Dk dielectric constant, dielectric loss tangent, volume and surface resistivity, resistivity, and electric strength.
DK: It involves the signal strength and impedance that show how that material performs electrically. Generally, the PCBs Dk value ranges from 3.5 to 5.5, and this value may or may not change, depending on the PCB material. The high-frequency PCBs must have a stable Dk.
Tan δ, Dielectric Loss Tangent: It determines the power like if the loss tangent is less, the material will lose minimum power. In the case of PCB, the dielectric loss tangent of materials can be 0.02 to 0.001. The loss tangent is not so important in the case of digital circuitry.

PCB Material’s Volume Resistivity: Sometimes the dielectric material resists electricity or insulation and that quality is called the volume resistivity. If a PCB material comes up with high resistance, its electric charges would not be much. Weather conditions or temperature also affect the resistivity of a PCB material, like moisture, cold, heat, etc.

Dielectric Materials Surface Resistivity: If the surface of a dielectric material resists insulation or electricity, it is known as surface resistance. This property gets affected due to moisture and extreme cold or heat.

Electrical Strength of A Dielectric Material: It occurs along a PCBs Z-axis where the dielectric material resists the electric breakdown and we call it an electrical strength. Generally, the PCB materials come up with 800 V/mil to 1500 V/mil of electric strength.

Thermal Properties of A PCB Material

A PCB material’s thermal properties depend on the Tg, which is the glass transition temperature of that material, Td or decomposition temperature, CTE, coefficient of thermal expansion, and K, or thermal conductivity.

Tg: when the environment around a PC BOARD is too hot having a temperature above normal, the substrate gets soft. But, it goes back to its old state when taken away from heat, and this process is called the Tg or glass transition temperature.

Td: when a PCB substrate gets decomposed due to a high temperature, it loses some of its mass, and this temperature is known as decomposition temperature or Td. Unlike Tg, the deformation effects last forever. So, the PCB material should be compatible with the temperature of your environment. Generally, the temperature range, in this case, is from 200° C to 250° C.

CTE: It is the coefficient of thermal expansion, like the temperature at which a PCB material goes through expansion. You can measure it in ppm or parts per million. The CTE of a PCB substrate is higher than that of a copper layer, and it should be less across the axis. Generally, experts think of 70 ppm ideal in this case.

K, or thermal conductivity: It is the heat transfer property of a PCB, and the low K means that the heat transfer property of a material is less. Whereas, the high K value means the PCB material has a high heat transfer. You can measure it in w/m or watts per meter at K. The value of K in the case of a dielectric material ranges from 0.3 to 6W/MK., whereas this value is high for a copper layer.

PCB Materials Chemical Properties

These properties involve moisture absorption, flame-related specs, and methylene chloride resistance. Let’s look at these properties to understand them better.
Specifications of Flammability: electrical appliances or devices have certain components in plastic, which are vulnerable to fire. Plastics have specific flame-retardant properties known as flammability. PCB material has certain requirements in terms of flammability which means it cannot burn for more than 10 seconds in terms of flaming.
Materials Moisture Absorption: A dielectric material should be able to bear moisture when exposed to a liquid and that property is known as moisture absorption. Generally, most PCB materials have 0.01 to 0.02 percent moisture absorption, and it affects the thermal and electrical properties of a material.
What Is Methylene Chloride Resistance: This is another chemical property or resistance of a material being used for PCBs. Mostly the MCR of dielectric material is 0.01 to 0.02 percent.

PCB Materials Mechanical Properties

These properties are considered more for flex and rigid circuit boards. The mechanical properties involve peel strength, flexural strength, delamination time, and density. You can explore these properties in flex and rigid circuit boards.

HDI PCB Materials

The selection of dielectric material is hard because a wrong material sends wrong signals due to low-quality substrate and copper foil. The right material can help in having effective signals.

The PCB system involves several losses if its material is poor. Moreover, the copper conductors also cause a loss due to the electrons being away from a conductor’s center.
So, choose your material carefully for proper electric signals to make a device more functional. You should select a material that is suitable for high-frequency PCB regarding foil and substrate. A PCB’s substrate has different materials, including glass fibers and epoxy. The dielectric constant of a substrate should be low to help designers have a high-frequency PCB.

On the other hand, the foil that you apply to the copper should be of high quality. You must use copper with minimum resistance. In other words, the foil and substrate should be compatible, as incompatibility can result in a big loss. The foil should be smooth, moreover, it should be conductive because poor conductors can damage a circuit.

You must invest some money in PCB material to get an effective product. Some people use the FR4 just because of its low cost which is wrong, so don’t do that. Sometimes the PTFE has different defects, so choose it carefully. The material should be free from any manufacturing defects. Your printed circuit board can work for several years if you choose the right material, considering the above things. However, you should also be very clear regarding the application of a printed circuit board.

Conclusion

When choosing a material for circuit boards, you have to see their properties in terms of thermal, chemical, electrical, and mechanical properties. Let’s study these properties in detail and material types.
The selection of dielectric material is hard because a wrong material sends wrong signals due to low-quality substrate and copper foil. The right material can help in having effective signals.

The PCB system involves several losses if its material is poor. Moreover, the copper conductors also cause a loss due to the electrons being away from a conductor’s center. So, choose your material carefully for proper electric signals to make a device more functional. Your printed circuit board can work for several years if you choose the right material, considering the above things.

PNC Inc. has been a PC board manufacturer for the past 48 years and specializes in working side-by-side with visionary engineers and buyers in the High-Frequency RF/Microwave, Audio, Defense, and Medical industries (among others) to create solutions for ever-advancing printed circuit board concepts and designs.
Contact us at sales@pnconline.com to get more information related to the best PCB board material or pcb assembly.

Written by Sam Sangani

Sam Sangani is the President & CEO of PNC Inc., a Nutley, NJ based Printed Circuit Board manufacturer. Sam graduated from L. D. Engineering College with a BS Degree in Mechanical Engineering. He also continued his education and graduated from Steven’s Institute of Technology where he acquired a Master’s degree in Computer Science.

After completion of his BS, Sam worked as a QC Manager, for Xerox, Romania and London. He was responsible for the Quality Control of Cable and Wire Harness imports from Romania. After completing his Master’s Degree, he worked as a Senior Programmer with IBM, Tucson, Arizona. Sam was responsible for leading the Mainframe System Programming Team.

In 1997, Sam acquired PNC INC., a Nutley, NJ based PC Board fabrication Shop. From 1997-2013, Sam has made tremendous improvements and changes within PNC INC., as he added many new Products and Technologies in PNC’s portfolio. With his proven track record and leadership, PNC has never had an unprofitable year and has continued its growth yearly since 1997.

His current responsibilities are Strategic Planning, Corporate Management, New Business Ventures, Sales & Marketing, Trade Shows, Professional Services and leading productive teams to achieve peak potential. He has also utilized Lean Management techniques which have built a foundation for PNC’s high-paced growth. Sam also enjoys real-estate investing, web design & SEO, trading stocks, options, futures and Forex markets.