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How to choose PCB board correctly for PCB processing?
PCBA Tech
How to choose PCB board correctly for PCB processing?

How to choose PCB board correctly for PCB processing?

2021-10-30
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Author:Downs

The life and performance of circuit board processing depend on the choice of PCB board. In order to choose the correct PCB board, it is necessary to understand the materials used for different circuit board categories. Understanding the electrical and physical characteristics of different PCB boards helps to help circuit board processing and selection of boards.

When a large amount of current needs to be handled, the spacing and width of the circuit board are also important. The structural strength of the circuit board is determined by the substrate and laminate. The choice of materials for these two layers depends on the type of circuit board.

Circuit board processing PCB board composition and its significance

The PCB board consists of four layers, namely substrate, laminate, solder mask and screen printing. The substrate and laminate together define the basic electrical, mechanical, and thermal circuit board properties.

Substrate

Glass fiber FR4 is the most common material used for PCB substrates. Here, FR stands for flame retardant. It is suitable due to its rigidity and thickness. For flexible PCBs, use Kapton or equivalent plastics.

pcb board

The thickness of the PCB board depends on its application or purpose. For example, most Sparkfun products have a thickness of 1.6mm, while Arduino Pro products have a thickness of 0.8mm. PCBs made of cheaper materials such as epoxy resin lack durability.

Substrates are found in low-cost consumer electronics products. These have low thermal stability, which causes them to easily lose lamination. When the soldering iron is fixed on the board for a long time, the substrate can also cause smoke, which makes them easy to identify.

The non-conductive layer of dielectric material is selected based on the dielectric constant.

The substrate must meet certain required properties, such as the glass transition temperature (Tg). Tg is the point at which heat causes the material to deform or soften. A variety of materials can be used for the substrate, such as aluminum or insulated metal substrate (IMS) FR-1 to FR-6, polytetrafluoroethylene (PTFE), CEM-1 to CEM-5, G-10 and G-11, RF-35, polyimide, alumina and flexible substrates such as Pyralux and Kapton.

"In general, IMSes can minimize thermal resistance and conduct heat more efficiently. These substrates are mechanically stronger than thick-film ceramic and direct-bonded copper structures commonly used in many applications."

Laminate

This provides properties such as coefficient of thermal expansion, tensile and shear strength, and Tg. Common dielectrics used for laminates are CEM-1 and CEM-3, FR-1, FR-4, polytetrafluoroethylene (Teflon), FR-2 to FR-6, CEM-1 to CEM-5 and G-10.

The copper foil is the next layer laminated to the board. For double-sided PCBs, copper is applied to both sides of the substrate. The thickness of copper varies according to the application. For example, compared to low-power applications, high-power applications have a larger thickness.

Solder mask

This is the layer on top of the copper foil. It can be used as an insulating material for copper traces to prevent accidental contact with other conductive metals. It helps to solder in the right place.

It is a protective layer that prevents external contamination and provides the required isolation between surface components such as pads, copper wires, and drilled holes.

Silk screen

Screen printing is used to cover the solder mask layer, which is used to add letters, numbers and symbols on the PCB for ease of assembly and a better understanding of the circuit board through indicators.

Choose PCB board according to PCB type

Circuit boards can be classified in the following ways:

Component position: single-sided, double-sided and embedded

Stacking: single-layer and multi-layer

Design: based on modules, customized and special

Flexibility: rigid, flexible and rigid-flexible

Strength: electrical strength and mechanical strength

Electrical functions: high frequency, high power, high density and microwave

The board type can be used to select the most suitable board material for the design.

A single-sided PCB only includes a thin copper-plated substrate. Place a protective solder mask on the copper layer. The screen-printed coating can be applied on the top to mark the elements of the board.

The substrate of a double-sided PCB includes a metal conductive layer and components attached to both sides (top and bottom).

Multi-layer PCBs increase the density and complexity of PCB design by adding additional layers beyond those seen in double-sided PCB configurations. These allow extremely thick and highly compound designs. The additional layer used is the power layer, which provides power to the circuit and reduces the level of electromagnetic interference (EMI).

Rigid PCBs use strong rigid substrate materials (such as fiberglass) to prevent the circuit board from twisting. The motherboard in a computer is the best example of a non-flexible PCB.

The substrate of the flexible PCB is flexible plastic. It can be rotated and displaced during use without damaging the circuit on the PCB. It can restore heavy wiring in advanced gears where weight and space are critical, such as satellites.

Rigid-flex board consists of a rigid circuit board attached to a flexible circuit board. These boards can meet composite design requirements as needed.

Safety precautions for toxic materials in circuit board processing

The fumes in the solder may contain lead, which is toxic. Solder is used to make electrical connections on the PCB, so the soldering operation must be carried out in a closed environment. The smoke discharged into the atmosphere must be clean. One solution to replace wires and solder is to use water-soluble conductive molding plastics.

Precautions for choosing PCB materials for heat dissipation

The two factors that affect the PCB are power and heat. Therefore, it is important to determine each threshold. This can be done by evaluating the thermal conductivity of the PCB through the length of the material.

PCB materials with low thermal conductivity generate heat, which can be a huge disadvantage for heat-intensive applications.

PCB material selection for circuit board processing

There are two types of PCBs, single-sided and double-sided, some of which are copper-clad, while others use aluminum in the military and aerospace, automotive and medical industries. For these specific areas, the materials used should have the best performance.

The reasons for choosing PCB materials are their light weight, good quality or the ability to withstand high power. Since the material level is related to the performance level, it is important to determine which functions need to be compared with each other when selecting PCB materials.

Most of the flexible board is composed of Kapton, which is a polyimide film with heat resistance, dimensional consistency and dielectric constant of only 3.6. Kapton has three Pyralux versions: FR, non-flame retardant (NFR) and glue-free, high performance (AP).

Quality is important for the construction of any type of circuit board for household electronic equipment or industrial equipment. Components such as PCBs should provide excellent performance over the expected lifetime. Electronic equipment, microwave ovens and other household appliances rely on PCB technology to keep them working.

PCB board processing for LED lighting selection

The LED PCB board heats up during operation. Therefore, the LED chip is mounted on a base made of metals such as aluminum, copper or alloy mixtures and coated with a highly reflective surface to achieve optimal heat management and increase light output. This keeps the heat generating components cool and improves their heat dissipation capacity. This can improve the performance and life of the LED.

Therefore, choose a metal core PCB (MC-PCB) for LED applications. Including a thin layer of thermally conductive dielectric material, its heat transfer efficiency is much higher than the traditional rigid PCB. FR-4 material includes a layer of hot-dip aluminum, which can effectively dissipate heat. In view of the fact that MC-PCB materials are developed for higher power.