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As an electrical engineer or hobbyist, you may sometimes encounter overheating issues with your PCBs. When components heat up during operation, this can cause the PCB substrate to soften, warp, or lose its mechanical strength if temperatures exceed the glass transition point.
The result? Degraded performance and premature failure of your boards.
This is where high TG PCBs come in. With a glass transition temperature above 170°C, these boards retain their rigid structure even in hot operating environments.So if you’re dealing with lead-free soldering, high-power densities, or ambient operating temperatures above 130°C, a high TG PCB is likely your solution for reliable thermal management.
To know more, then read along with ELEPCB!
What is a High TG PCB?
First things first – what exactly is a high TG printed circuit board? A high TG or high glass transition temperature PCB is one designed to withstand temperatures above 170°C. The glass transition temperature (TG) refers to the point where the insulating substrate material transitions from a rigid, glassy state to a softer, rubbery state as it heats up.
Exceeding this temperature causes the board to lose its mechanical strength and desired electrical properties. A higher TG value indicates the PCB can operate reliably at higher temperatures before softening occurs.
Why Glass Transition Temperature Matters
The TG directly affects the stability and performance of a PCB. If your application generates significant heat, or experiences high external temperatures, choosing a board with a high enough TG is critical.
Once the operating temperature goes above the glass transition point, you can expect:
- Warping or deforming of the substrate
- Decline in mechanical rigidity
- Electrical failure
Types of PCBs by TG Rating
There are three main PCB classifications based on glass transition temperature:
- Standard FR-4 PCB: 130-150°C
- Medium TG PCB:150°C
- High TG PCB: ≥170°C
For demanding environments, high TG boards with a rating of 180°C or more are commonly used. Now that you know the key TG thresholds, let’s look at why high TG PCB materials are so advantageous.
Characteristics of High TG PCB Materials
There are several important traits that set high TG materials apart from conventional options:
Thermal and Mechanical Properties
High TG resins have enhanced resistance to heat, as well as improved mechanical performance at elevated temperatures. The materials retain their stiff, glassy properties at higher temperatures.
This results in greater stability and reduced risk of warping, expanding, or deforming under heat. It also prevents electrical failures induced by material softening.
1 Dimensional Stability
With high TG materials, PCB substrates better maintain their dimensions even when temperatures rise. This stability is essential for boards containing dense, finely-spaced traces.
2 Reliability of Plated Through Holes
High TG resins allow plated through holes (PTHs) to retain their integrity at higher operating temperatures. This is especially important for boards with small, high-density PTHs.
3 Thermal Stress Resistance
The materials are designed to withstand repeated, cyclical heating without cumulative damage. This makes them well-suited to environments where temperature fluctuations are commonplace.
4 Low Coefficient of Thermal Expansion
Many high-TG resins boast low Z-axis CTE values. This minimizes expansion and contraction of boards along the thickness direction as temperature varies.
In summary, high TG PCB materials offer enhanced performance and longevity in demanding thermal conditions compared to standard glass epoxy (FR-4) substrates. Their exceptional stability and reliability under heat make them an ideal choice for certain applications.
So let’s take a look at what kind of properties high tg pcb marterial specifically has and what are the advantages?
Why Choose High TG PCB Materials?
Now that you know the benefits of high TG boards, here are some of the top reasons to choose these materials:
Reliability in High-Temperature Environments
The superior thermal properties of high TG materials translate to greater reliability. By minimizing material degradation, you safeguard performance and extend the operating life of PCBs in hot environments.
Managing Heat Dissipation in Dense PCBs
HDI boards with fine features require materials that can cope with internally generated heat. High TG resins maintain stability even when heat builds up in compact multi-layer PCBs.
Dimensional Stability for Lead-Free Soldering
The Resilient Advantage of High TG PCBs
For HTG PCBs, toughness was reflected not only in the physical respect but also in its adaptability to extreme temperature changes. By selecting high-performance resins as binders, together with specially treated copper foils and reinforcing fiber cloths, HTG PCBs reduce the stress concentration during thermal expansion and contraction, avoiding cracks and thus effectively improving fatigue strength.
For applications pushing the boundaries of temperature tolerance, high TG PCB materials deliver marked improvements in thermal performance, longevity, and resilience.
How to Use High TG PCBs?
What is TG Value and How to
Choose the Right TG Value for a Pcb?
The Basic Concept of TG Value
In material science, TG stands for Glass Transition Temperature and is the temperature range beyond which amorphous polymers change from the hard glassy state to the flexible, highly elastic state.
In other words, this temperature is the point where, from its solid state, a material starts to get rubbery and moldable, specifically for substrate materials like FR-4, where the epoxy binder stays hard below TG and exhibits rubbery flexibility beyond.
Note that crossing the TG is not an instantaneous change but a softening process, often gradual; and provided the resin breakdown point is not reached, it will return to its original hardness upon cooling.
The higher the TG value of any board, the better the heat resistance. For high-temperature producing processes like lead-free soldering and surface tinning, high TG materials will highlight their irreplaceable value.
How to Choose a right TG Value?
Whereas the standard TG sheets are set above 130°C, High TG surmounts through over 170°C, and between them, the Medium TG stays roughly at around 150°C.
High-TG boards have superior properties that are conducive to their finding extensive usage in the high-end multilayer circuit board above at least 10 layers, automotive electronics, packaging technology, active and passive embedded components, precision industrial control equipment, and network communication gear.
- The increase in the value of TG is indicative of a significant improvement in the heat stability of the board, its resistance to moisture, and its resistance to chemicals.
- On the other hand, high TG material has higher strength and is more brittle than conventional material; this may reduce the speed of the PCB production process, especially in the drilling phase.
- The best option for medium to high TG grades is preferred when designs tend to be dense, with the vias very much close to each other. Such materials allow tighter vias since standard TG supports minimum spacing at 12 mils, while medium TG can be as close as 10 mils.
- High TG is hard, but the use of a fresh drill bit avoids pulling damage during drilling, thus preventing the so-called “wick” phenomenon.
That is to say, the higher the value of TG, the better the heat resistance and shape stability of the sheet. However, all the hardened properties of a high TG plate require higher processing temperatures at the same time, and the finished boards also become hard and brittle, affecting indirectly the quality of drilling and electrical performance in subsequent processes; considering costs, material selection shall be made to precisely meet the needs.
When Should You Use a High TG PCB?
For more modest thermal requirements, standard FR-4 or medium TG boards may suffice. But when conditions get extreme, high TG PCBs shine.
You gain the most benefit from a high TG board when:
- The operating temperature will exceed 130°C. Standard FR-4 materials soften soon above this point.
- The thermal load is within 25°C of the TG rating. This small safety margin prevents exceeding the glass transition point.
- Lead-free soldering is required. The higher melting point demands a substrate that stays rigid at 180-250°C.
- HDI PCBs with densely packed traces generate substantial internal heat during operation.
- The application involves high power density resulting in elevated temperatures.
Applications of High TG PCBs
Thanks to their exceptional stability and reliability under heat, high TG printed circuit boards play a vital role in many industries:
Aerospace and Aviation
Avionics equipment faces temperature swings from -55°C to 125°C. High TG boards withstand these conditions in flight control systems, engine controls, and navigation electronics.
Automotive
Underhood electronics in cars contend with ambient temperatures approaching 150°C plus, self-heating. High TG PCBs last longer in engine control modules, ABS, sensors, and infotainment systems.
Military and Defense
Mission-critical systems in the defense sector require unfailing performance despite shock, vibration, moisture, dust, and high temperatures. Rugged high TG boards deliver.
Medical
High TG materials withstand repeated sterilization up to 150°C in medical electronics like imaging systems, monitoring devices, and diagnostic equipment.
Telecommunications
Base stations and networking hardware endure ambient temperatures up to 85°C. High TG PCBs maintain signal integrity in these hot environments.
Industrial
Process control and automation systems must survive hot factory conditions. High TG boards support reliable operation in manufacturing facilities.
When You Need a High TG PCB
High operating temperatures arise in many fields, making high TG PCBs a versatile solution in sectors from transportation to medicine to telecom and beyond.
Here are a few key indicators that a high TG board would be beneficial:
- Your device or system operates at 130°C or higher. Exceeding standard FR-4 limits.
- The PCB experiences thermal loads less than 25°C below Tg. Too close to the glass transition point.
- You require RoHS compliance for lead-free soldering at elevated temperatures.
- Your product has dense multilayer PCBs where heat is concentrated internally.
- High-power components on the board produce localized heating.
In scenarios like these, a high TG PCB helps prevent early failures and ensures stable performance in hot environments.
High TG Materials Used in PCB Manufacturing
Many material suppliers offer high TG resins designed to excel in PCB fabrication.
Some popular options include:
Material Supplier | Material Name | TG(℃) |
|---|---|---|
Isola Materials | FR370HR | 180 |
Isola Materials | P95 | 260 |
Isola Materials | I-Speed | 180 |
Isola Materials | I-Tera MT40 | 200 |
Isola Materials | Tachyon 100G | 192 |
Rogers Materials | RO4350B | 280 |
Rogers Materials | RO4003C | 280 |
Rogers Materials | N4380-13 | 210 |
Nelco Materials | N4000-13SI | 210 |
Nelco Materials | N4800-20 | 180 |
Panasonic Materials | R-1755V | 180 |
Panasonic Materials | 170 | |
Ventec Materials | VT-47 | 180 |
This list highlights some excellent high TG resin systems ranging from 180°C up to 280°C. Many additional options exist to suit specific thermal, electrical, and mechanical requirements. An experienced PCB manufacturer can help recommend the optimal material choice.
Conclusion
In conclusion, high TG PCBs enable stable performance in hot environments where standard boards falter. Consider using them if you’re pushing the boundaries of temperature tolerance in your application. With their exceptional heat resistance, high TG boards prevent failures induced by material softening.
FAQs
A1: Lead-free solders melt at around 180-250°C, much higher than the 130-150°C for tin-lead solders. High TG PCBs are required to withstand these temperatures.
A2: Yes, high TG PCBs work fine with standard tin-lead solders. Their higher thermal resistance still provides benefits.
A3: Polyimide and cyanate ester are two robust high TG resin systems commonly used for aerospace and defense PCBs.
A4: Ceramic substrates have even higher heat tolerance but lack the flexibility of resin-based high TG boards.
A5: No, extremely high temperatures exceeding the TG will eventually cause warping. But high TG boards raise this failure threshold significantly.
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