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Printed Circuit Board(PCB) Glass Transition Temperature(Tg)

Posted:03:32 PM September 23, 2022 writer: NextPCB

What is PCB Tg?

The printed circuit board(PCB) glass transition temperature(Tg) of a polymer system is the temperature at which the material changes from a relatively stiff, "glassy" state to a more pliable or softened state. This thermodynamic material change is reversible as long as the polymer system has not degraded. In other words, when the material gets heat above Tg and then cooled to Tg, it returns to a stiffer state with basically the same properties as before.

The vast majority of base materials have an organic content. At the very least, PCB base binders, hydrocarbons, have relatively lower temperature stability than the inorganic constituents of composite materials.

Many years of efforts by chemists improved the thermal properties of polymers good to use as binders. However, these properties still remained far from the thermal stability of reinforcing glass fibers, ceramic fillers, and metal foil.

Good to use in widespread lead-free technologies, at first glance, a slightly increased soldering temperature, in fact, turned out to be significantly exceeded the temperature stability of the polymers of the printed circuit board binders.

The Most Important Properties of PCB Tg Material

The most important property of dielectric printed circuit board substrates is their thermal expansion in the transverse direction, i.e. across the reinforcing fibers - along the Z axis. This becomes especially true for HDI boards, which distinguish by the use of thin plated holes in thick board bases.

The difference in thermal expansion of the base and the metal in the holes could lead to a significant decrease in the reliability of the interconnectors.

However, if the material has been heated to a temperature much higher than Tg, then irreversible changes in its properties may occur. The temperature at which this occurs varies with the type of material and is relevant to the degradation of the polymer.

PCB Tg Class

High Tg PCB

We always implicitly mean that higher values ​​of Tg are always better. But it is not always the case. While it is true that higher Tg values ​​will delay the onset of intense thermal expansion for a given polymer system, the overall expansion may still differ from material to material. A material with a lower Tg may exhibit less net expansion than a material with a higher Tg.

High Tg Ratting

Quality Grade: Standard IPC II

As electronic devices become more diversified, printed wiring board materials are required to have higher heat resistance.

There are glass transition temperature (Tg), thermal decomposition temperature (Td), and relative temperature index (RTI) as indices for evaluating this heat resistance, but PCb Tg (= glass transition temperature).

Tg is the temperature at which the physical properties of thermosetting resins such as phenol and epoxy change from glassy to rubbery when heated. When the temperature reaches around this temperature, physical properties such as:

  • the mechanical strength and
  • dielectric constant of the resin change greatly

So printed wiring board materials are required to have a high Tg point.

PCB High Tg Material

  • FR4, High-TG, Halogen Free, Rogers, Aluminum Base
  • Measurement method of glass transition temperature (Tg)

There are two methods for measuring Tg: (1) Dynamic viscoelasticity measuring device (DMA), (2) thermo mechanical analyzer (TMA), and (3) differential scanning calorimeter (DSC). In general, in order to know the mechanical properties of a material, a uniform, unidirectional load such as tension, bending, or compression is applied. On the other hand, DMA is characterized by giving vibration

Application of High Tg PCB

High power lights: led street light, led flood light, led high bay light, led work light.

Special lighting: traffic lights, led gardening lights for plant growth; UV printer led lights, medical UV lights, beauty UV lights.

Median Tg PCB Material

This is a test method in which a reference material whose thermal expansion increases linearly at a constant rate within the measurement temperature range and a sample are simultaneously heated at a constant rate.

Black G-10 CS-3525

Resistance characteristics of printed wiring board materials required by the industry (class B ÿ middle-end applications) and the development trajectory of Rishorite high heat resistance printed wiring board materials is black.


This is a black G-10 material developed using our original curing system, based on resin blends of materials classified as G-10 by ANSI standards. Black G-10 achieves a Tg of 160°C, whereas the Tg of general G-10 material is about 120°C. At that time, the industry had begun to use direct bonding

G-10, developed in 1975, was the pioneering material for RISHOLITE high heat-resistant printed wiring board materials.

Mediam Tg Ratting

FR-1, FR-4, CEM-3, etc. are terms that are often common when referring to printed circuit boards. These terms describe the type of printed circuit board and are determined by the base material and resin good to use for the printed circuit board.

This article describes the types and classifications of printed circuit boards.

PCB Middle Tg Material

Substrates typically come by their:

  • insulating properties
  • material composition
  • and flame resistance
  • Similarly, common raw materials include bakelite
  • glass cloth, and various plastic boards

PCB board manufacturers generally press copper foil with an insulating prepreg made of glass cloth and epoxy resin to create a copper foil board.

Rigid substrates use non-flexible insulators as the base material and are called rigid substrates from the word "rigid," which means hard.

Flexible substrates, on the other hand, use a flexible insulator as the base material. In most cases, the term printed circuit board simply refers to a rigid circuit board.

Rigid substrates are classified according to the base material and resin good to use. Generally, "paper base material" and "glass cloth base material" are good to use as the base material, and "phenol resin" and "epoxy resin" are good to use as the resin.

Application of Median Tg PCB

  • Single-sided substrates are a common application for paper phenolic substrates
  • White goods, stereos, radio cassette players, home phones, game consoles, keyboards, etc.

It is good to use for silver through-hole substrates in which through-holes cannot be formed by copper plating, but silver paste is filled into the holes to form through-holes.

Low Tg PCB Material

A symbol representing base material

  • P → Paper base
  • G → Glass fabric base

Symbol representing resin

  • P → Phenolic resin
  • E → Epoxy resin
  • I → Polyimide resin
  • T → Bismaleimide/Triazine/Epoxide

Low Tg Ratting

The term T g of a polymer system has several meanings. They include:

Thermal expansion and its change during the transition through Tg ; are the degrees of hardness of the polymer system before and after Tg . Negative measurement differences of these values, or negative Tg when Tgl is greater than Tg2, also indicate a complete cure. However, great care must be taken when using these methods to evaluate the degree of cure.

Not all polymers will perform the same in sequential tests like this one. The degree of cure for some modern polymer systems is not always easy to assess using these methods. In addition, sample preparation methods, in particular their heat treatment before testing, can also affect the results of the analysis of the degree of cure of the binder.

Common FR-4 Tg

Fr-4 Tg 130

TG130 indicates a temperature range where FR-4 would be caused, which is 130 degrees Celsius. It will gradually become softer. TG 130 will return to its original qualities once it has cooled.

It is the most widely used FR-4 material and offers the best insulation qualities, arc resistance, low water absorption, and manufacturer familiarity.

Fr-4 Tg 140

The primary temperature foundation for printed circuit boards is Fr4-Tg140. We mean that once you choose to operate it at a temperature above 140 degrees, the basic material of your printed circuit boards will become unstable.

FR-4 Tg 150

Once you choose to operate at a temperature above 150 degrees, the basic material of printed circuit boards will become unstable. You'll be able to determine your temperature's operational limit by keeping 150 in mind as the Tg value. As long as you keep your temperature below 150 degrees, the PCB foundation will continue to be mechanically stable.

Fr-4 Tg 155

It goes without saying that a typical PCB FR4-Tg is between 130 and 140 degrees, a medium Tg is above 150 to 160 degrees, and a high Tg is above 170 degrees. High FR4-Tg will be more heat- and moisture- resistant mechanically and chemically. The better the material resists temperature, the higher the Tg value, hence high Tg is becoming more and more common, especially in lead-free processes.

Fr-4 Tg 170

Printed circuit board solid materials transform into a rubber-like material at a high temperature for glass transition known as Fr4 Tg. Fr4 Tg170 has excellent heat resistance and anti-CAF characteristics. These characteristics will make your product more durable.

Fr-4 Tg 180

High temperature resistance, long-term delamination endurance (materials ageing for safety reasons), and low thermal expansion are all properties of Fr-4 Tg 180.

What is PCB Thermal Decomposition (Td) Temperature?

All materials change their physical dimensions in response to changes in temperature. The coefficients of expansion of glass fiber reinforced material differ along the respective axes due to the direction of the reinforcement. In length and width, the laminate or PCB occupies the X, Y plane, while the Z axis is perpendicular to that plane.

The rate at which the material expands is much slower at temperatures below Tg than at temperatures above that value. Thermomechanical analysis (TMA) measures dimensional changes as a function of temperature. Extrapolation of the linear sections of the curve towards the point at which they intersect gives an estimate of the value of Tg.

The slopes of the linear sections of this curve above and below T g represent the relative rates of thermal expansion, or as they are commonly called, temperature coefficients of expansion (TEC). The CTE values ​​are very important as they affect the reliability of the board.

This extension is much larger in the transversal direction. In the reinforcement direction, it restrains by a glass cloth having a relatively low CTE. Therefore, less thermal expansion along the Z-axis will mean a greater degree of reliability and less stress exerted by this expansion on the plating of the holes.

New Materials in PCB Tg

The general trend shows a continued decrease in the dielectric constant (Dk) and dissipation factor (Df). for the production of printed circuit boards with low losses. The acceptance of new materials into production influences both by their ease of manufacture and their overall cost.

Providing higher computing performance, but more expensive materials are not in demand on the market. Moreover, less functional materials, but produced in large volumes similar to FR-4.

Price-sensitive thermoset alternatives to PTFE have been rapidly developing in the manufacture of materials with low Dk and Df. However, in some cases, materials with a higher dielectric constant have proven to perform better in structural applications where capacitance needs to form.

Another new material proposed is a heat-conducting dielectric. This material allows much better heat dissipation from the more powerful processors of modern computers.

PCB Tg Coefficient Of Thermal Expansion(CTE)

The coefficient of thermal expansion depends on the composition of the components of the base material and their relative concentrations. The polymer system has a higher coefficient of thermal expansion compared to fiberglass or other inorganic materials good to use for reinforcement.

When controlling z-expansion, the key factors to consider are the type of polymer system, its glass transition temperature, and the proportion of polymer in the base material. To lower the CTE coefficient of the material, other fillers can be good to use in addition to the glass cloth.

We compare the thermal expansion coefficients of several commercially available base materials. Values ​​given may vary significantly depending on the exact resin content of the material or PCB under test.

In multilayer printed circuit boards, the copper content of the sample will also have a noticeable effect. The expansion of copper in the z-axis is very low compared to the polymer system.

CTE Values in PCB Tg

Attention is drawn to the general change in the CTE values ​​as T g increases. The higher Tg delays the onset of the rapid expansion that occurs after reaching the glass transition temperature. It is also noteworthy that filled materials show lower levels of z-axis expansion compared to similar unfilled materials.

Time-to-delamination tests have gained considerable attention as lead-free technologies have become widespread. It is important not to to focus one characteristic or type of measurement when specifying a material for lead-free soldering technology.

First, the correlation between the time to delamination and the suitability of a given material for lead-free assembly is not always clear.

Long gaps in T260 or T288 alone do not guarantee a high degree of reliability in connection with lead-free soldering. Conversely, some materials with sufficient, but not necessarily large T260 or T288 spacings show excellent performance for lead-free soldering applications.

It is important to consider this characteristic, as the time to delamination. It should not be the only one when determining suitable materials for lead-free soldering. Successful application in lead-free technology requires a balance of several material properties.


Unlike domestic manufacturers of base materials abroad, there is an intensive search for improving the quality characteristics of base materials for printed circuit boards. This is not only due to the increasing use of lead-free soldering technologies. It is equally important that the sealing of interconnects by reducing the diameter of the holes leads to high loads on the metallization due to the intensive expansion of the dielectric bases.

In order to reduce the CTE of printed circuit board bases in the transversal direction, intensive development and production of polymer systems with high glass transition temperatures are underway in order to shift the increase in CTE to higher temperatures.

The need to use lead-free soldering technologies associated with higher temperatures has made it important to characterize the resistance of materials to thermal degradation.

The requirements for the completeness of polymerization of the binder, its testing, and post-polymerization methods by using the thermal stabilization operation have become more significant.

Tag: Tg
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