Why PCB HTG Material Isn’t Always Better, Beyond 180°C, Guide to PCB Tg

When pursuing high-performance and reliability in PCBs, high-Tg materials (Glass Transition Temperature) are often the go-to choice. But is you understanding still stuck in the “higher Tg is always better” mindset? While materials like ISOLA P96 with Tg 260°C and VT90 with Tg >250°C exist, as a former lamination and materials engineer at TRIPOD, I offer a counterintuitive perspective: blindly pursuing high Tg carries unforeseen risks.

PCB HTG Material

1. What Exactly is Tg?

Tg, or Glass Transition Temperature, is the critical point at which a PCB’s substrate (like the resin) transitions from a rigid, glassy state to a soft, rubbery one. When operating temperatures exceed the Tg, the material’s mechanical strength drops significantly, and its coefficient of thermal expansion can change abruptly, potentially compromising long-term reliability. Thus, Tg is a key indicator of a material’s heat resistance.

2. Two Primary Methods for Testing Tg

DSC (Differential Scanning Calorimetry): Measures the change in heat flow as the material is heated to determine Tg. It offers high precision and is ideal for R&D and detailed analysis.

TMA (Thermomechanical Analysis): Determines Tg by monitoring the material’s dimensional changes under heat. This method more directly reflects the board’s thermal expansion behavior in the Z-axis (thickness direction) and is more commonly used in the PCB industry.

3. The Unspoken Risks: Why I Don’t Blindly Recommend High-Tg (PCB HTG Material)

Based on my experience handling customer complaints at TRIPOD, approximately 80% of PCB delamination cases were linked to high-Tg materials that had been stored for over six months before undergoing SMT reflow soldering. The core risks are:

Moisture Absorption Risk: The resin systems in high-Tg materials are often more polar, making them hygroscopic (prone to absorbing moisture from the air). If not properly baked before reflow, the trapped moisture vaporizes instantly during soldering, creating immense internal pressure that causes delamination or “popcorning.”

Cost-Performance Balance: Most applications do not require extreme Tg.

For cost-sensitive products (like consumer electronics) with generous via spacing, Tg130 FR-4 is common. However, to achieve this low cost, fillers are often added, which can reduce resin flow and increase the risk of ICD (Inner Copper Dissociation).

For durable goods and automotive electronics, we most frequently recommend Mid-Tg (around 150°C) materials. They offer the best balance of heat resistance, moisture performance, and cost, satisfying most demanding applications with a wider process window and higher overall reliability.

4. Our Professional Recommendation: Control Where It Matters Most

Selecting the right laminate is an exercise in balance, but its performance is only fully realized through precision manufacturing. At SQPCB, we’ve made significant investments to ensure exactly that.

Our production lines are equipped with automated LDI for inner-layer and solder mask imaging, as well as automated inkjet legend printing. This eliminates the variability of traditional film-based exposure—preventing shrinkage, misalignment, and manual handling errors. The result is higher first-pass yield, significantly reduced scratches, foreign object contamination, and rework, while ensuring superior solder mask gloss and definition.

Furthermore, we maintain in-house lamination, HASL, and ENIG surface treatment lines. This vertical integration gives us direct control over quality and turnaround time, insulating your projects from supply chain delays and external processing inconsistencies.

Let us help you navigate the trade-offs:
• SQPCB Instant Quote Platform: https://www.sqpcb.com
• Contact Our Engineering Team: https://www.sqpcb.com/contact

Our engineering team leverages this controlled manufacturing ecosystem to recommend materials that best fit your product’s application, budget, and lifecycle needs—mitigating risks and ensuring reliable outcomes.

5. FAQ: PCB Tg Answered

Q1: Is a high-Tg PCB board always “better” than a standard-Tg PCB board?
A: Not necessarily. “Better” depends on the application. While high-Tg offers superior stability at elevated temperatures, it also comes with higher processing difficulty, moisture absorption risk, and cost. For applications not subjected to high temperatures, Mid-Tg materials are often more economical and reliable.

Q2: What Tg should I choose for a board that undergoes double-sided reflow?
A: Double-sided reflow demands good heat resistance. Generally, a Tg of 150°C or above is recommended. The final choice should consider peak temperature, board design (e.g., heavy copper, thick cores), and other factors.

Q3: How can I prevent delamination in high-Tg boards that have been stored for a long time?
A: The key is moisture management. Strictly follow the material’s MSDS (Material Safety Data Sheet) and implement a pre-bake cycle before SMT to drive out absorbed moisture.

Q4: Is high-Tg material mandatory for automotive electronics?
A: Automotive requirements vary. While under-hood applications near the engine might require Tg150 or higher, many infotainment and body control modules are perfectly suited for Mid-Tg (Tg150) materials, which are often preferred for their robust processability.

Q5: What’s the difference between Tg and Td (Decomposition Temperature)?
A: Tg is the temperature at which the material softens. Td is the temperature at which the resin begins to decompose chemically and irreversibly. For lead-free soldering, Td is a critical metric for long-term reliability, as it defines the material’s ultimate thermal endurance limit.