High Temperature PCB Design is the necessity of High-Temperature Electronics that pose Design and Reliability challenges. High Temperature PCB ( High Tg PCB ) is a good choice for electrical equipment of the high temperature environment. Electrical equipment will be better performance, use High-Temperature PCB in high-temperature state. Many industries are calling for electronics that can operate reliably in harsh environments, including extremely high temperatures. Because of the RoHS compliance, Lead-free soldering technologies also asking for High Temperature Printed Circuit Boards to sustain with the large heat applied during soldering and components assembly.

Why High Temperature Printed Circuit Boards Needed?

Traditionally, engineers had to rely on active or passive cooling methods when designing electronics that must function outside of normal temperature ranges. But in some applications, cooling may not be possible, or it may be more appealing for the electronics to operate hot to improve system reliability or reduce cost.

In the past, high-temperature electronics designers were compelled to use standard-temperature components well above their rated specification due to the unavailability of high-temperature ICs. Fortunately, recent IC technology has produced devices that can operate reliably at very high temperature, more than 150 degree Centigrade.

With the availability of high-temperature components, electronics engineers eliminating the cooling methods in their system design, to reduce the size and cost of the design. But now the regular PCB itself is a potential source of failure. at high temperature working environments. Now it’s the time to upgrade the PCB technology to sustain in high-temperature operating conditions without any cooling techniques.

What is High Temperature PCB?

High Temperature PCB is also called as “High Tg PCB“. Tg means Glass Transition Temperature. The glass transition temperature (Tg) is an important normative dimension for the base material that determines the temperature at which the resin matrix converts from a glassy, brittle condition into a soft, elastic one. Commercially available PCBs have Tg of 170C. When the glass transition temperature (Tg) is over 170°C, it is referred to as a high Tg material. High Tg PCB will provide better performance for high-temperature applications.

The base materials of PCB, under the conditions of high temperature, will easily soften, deform, or melt, and has the mechanical and electrical features sharply declined. If the temperature exceeds designated Tg value, the board will changed from glassy state to rubbery state and then the function of board will be affected. The Tg value of the base material sets here an upper boundary, at which the resin matrix decomposes and a subsequent delamination occurs in multilayer PCBs.

High Tg materials have the following properties:

  • High glass flow temperature value (Tg)
  • High temperature durability
  • Long delamination durability
  • Low Z axis expansion (CTE)

Generally, the differences between common FR-4 material and high Tg FR-4 material include: under the heat conditions, especially heating after moisture absorption, high Tg materials have better mechanical strength, dimension stability, adhesiveness, moisture absorption, thermal decomposition, and thermal expansion than that of common PCB base materials.

High Temperature PCB Selection Tips

The Tg is thus NOT the value of the maximum operational temperature, but rather that which the material can endure for only a very short time. A guideline for a continuous thermal load is the maximum safe operating temperature is approximately 25°C below the Tg.

If working temperature of your product is higher than normal (130-140C), then have to use high Tg material which is > 170C. If working temperature is higher than 170/180C, such as 200C, 280C, or even higher, then you’d better use Ceramic board which can go through -55 to 900C.

Typical Applications for High Temperature PCB Design

  • High-Temperature Electronics Testing Boards
  • Oil and Gas industries
  • Aerospace and Avionics
  • Military/Defence and Space Applications
  • Industrial electronics
  • Automobile electronics
  • LED Luminaries