Shengyi ST115G is a halogen-free, high-thermal-conductivity copper-clad laminate for PCB designs that need more through-board heat spreading than ordinary glass-epoxy material while retaining electrical insulation. The official datasheet positions it for PCB heat-dissipation solutions, automotive electronics, LED headlamps, intelligent terminals and SSDs.
Its value cannot be reduced to “1.6 W/m·K FR-4.” Shengyi publishes two thermal-conductivity results under different ASTM methods, and neither number alone predicts component junction temperature or finished-board thermal resistance. At QFPCB, we review the complete copper pattern, stackup, vias, board thickness, heat source, interface and cooling path before confirming an ST115G construction.
What Is Shengyi ST115G?
ST115G is the copper-clad laminate; ST115GB is its matching bonding prepreg. Shengyi describes the system as a high-thermal-conductivity multilayer material with halogen-free construction, high CTI, low Z-axis expansion and lead-free-process compatibility.
The material uses inorganic filler to improve thermal behavior. That filler also changes fabrication: the official processing guide describes greater hardness, lower drilling efficiency, more difficult desmear and higher router wear. Selecting ST115G therefore changes both thermal design and manufacturing planning.
ST115G Datasheet Values and Test Conditions
The following table uses Shengyi document CN-TDS-2009-04-ST115G-ST115GB. Values are typical references, not specification limits. Shengyi states that most results use a 1.0mm specimen, while Tg uses a specimen at least 0.50mm thick.
| Property | Typical value | Condition | Unit | Method |
|---|---|---|---|---|
| Thermal conductivity | 1.6 / 2.0 | Condition A | W/(m·K) | ASTM D5470 / ASTM E1461 |
| Tg | 170 / 175 | DSC / DMA | °C | IPC-TM-650 2.4.25C / 2.4.24.4 |
| Td | 410 | TGA, 5% weight loss | °C | IPC-TM-650 2.4.24.6 |
| T288 / thermal stress | >30 / >30 | TMA / 288°C solder dip | min | IPC-TM-650 2.4.24.1 / 2.4.13.1 |
| Z-axis CTE | 37 / 166 / 2.2 | Before Tg / after Tg / 50-260°C | ppm/°C / % | IPC-TM-650 2.4.24 |
| Dk / Df | 5.10 / 0.0104 | 1GHz, C-24/23/50 | – | IPC-TM-650 2.5.5.9 |
| Arc / dielectric breakdown | 200 / >45 | D-48/50 + D-0.5/23 | s / kV | IPC-TM-650 2.5.1 / 2.5.6 |
| Peel strength | 1.05 | 1oz copper, 288°C/10s | N/mm | IPC-TM-650 2.4.8 |
| Water absorption | 0.11 | E-1/105 + D-24/23 | % | IPC-TM-650 2.6.2.1 |
| Flammability / CTI | V-0 / PLC 0 | Published conditions | rating | UL 94 / IEC 60112 |
Why ST115G Has Two Thermal-Conductivity Values
Shengyi reports 1.6 W/(m·K) by ASTM D5470 and 2.0 W/(m·K) by ASTM E1461. These methods do not create two interchangeable specifications. Test configuration, heat flow and data reduction differ, so a supplier comparison must use the same method, specimen and condition.
Laminate conductivity is also not the thermal resistance from a component junction to ambient. Copper planes, thermal vias, dielectric distance, board area, solder joints, thermal interface material, enclosure and airflow form the real path. Use the official numbers as material inputs, then validate the assembled thermal design.
ST115G Versus Standard FR-4 and Metal-Core PCB
ST115G offers a glass-reinforced multilayer route when ordinary FR-4 does not spread heat adequately. It supports multilayer interconnects and insulation without requiring a metal base, but it should not be marketed as equivalent to aluminum, copper-base, ceramic or DBC constructions.
A metal-core PCB can provide a different heat path through a thin dielectric into a metal base. ST115G may be preferable when multilayer routing, plated holes or electrical isolation across a conventional laminated structure matter. The correct comparison is thermal resistance of the complete build, not a single conductivity number.
High CTI, Halogen-Free Status and Electrical Limits
The datasheet reports CTI PLC 0 under IEC 60112 and V-0 under UL 94. These are useful inputs for tracking resistance and flammability decisions, but they do not automatically establish creepage distance, working voltage, pollution degree or end-product certification.
Halogen-free status must remain tied to the exact ST115G/ST115GB system and customer compliance documentation. Do not infer that every solder mask, ink, adhesive or assembly material in the finished PCB is halogen-free because the laminate is described that way.
ST115GB Prepreg, Pressing and Storage
ST115GB is offered in filler-rich prepreg constructions that differ from familiar general-purpose FR-4 glass styles. The official sheet lists the following reference options.
| Glass style | Resin content | Cured thickness | Standard roll size |
|---|---|---|---|
| 1080 | 85% | 138µm | 1.260m × 150m |
| 106 | 90% | 105µm | 1.260m × 150m |
| 1027 | 88% | 72µm | 1.260m × 150m |
| 1027 | 90% | 86µm | 1.260m × 150m |
The TDS reference cycle uses a 2.5-3.5°C/min heat-up rate from 80°C to 140°C and more than 90 minutes above 190°C. The detailed processing guide gives construction-dependent guidance: 2.5-4.0°C/min for inner copper at least 3oz, 2.0-3.0°C/min for inner copper up to 2oz, 300-420psi high pressure and cure above 90 minutes at 180-200°C. QFPCB sets the production cycle from the actual fill area, prepreg quantity and copper distribution.
Sealed prepreg storage is three months below 23°C and 50% RH, or six months below 5°C. The processing guide requires at least eight hours of normalization before opening cold storage and recommends using opened sheet prepreg within three days or retesting it.
Drilling, Desmear and Routing Risks
ST115G is harder and more filler-rich than standard FR-4. Shengyi recommends reducing drill infeed by approximately 5-10% from high-Tg FR-4 settings, observing hit-count limits and using coated drills; diamond-coated tools are preferred in the guide. These are starting recommendations, not a universal production recipe.
The inorganic filler makes resin removal more difficult, so desmear needs additional attention. Shengyi recommends ultrasonic rinsing and notes that a 150°C, four-hour post-drill bake may strengthen the desmear result. Routing-tool wear is also higher, and feed may need reduction. The material is not suitable for punching or V-cut-style shearing as a substitute for routed profile processing.
Multilayer, HDI and Impedance Stackup Review
For multilayer PCB manufacturing, QFPCB reviews heat flow together with resin filling, copper balance, layer registration, hole structure and warpage. ST115G is not in our current general FR-4 capability baseline, so the exact grade, laminate thickness, ST115GB construction and present availability require quotation-stage confirmation.
An HDI PCB may be evaluated when the project-specific ST115G construction is approved, but filler, thin dielectric selection, laser-via behavior, copper filling and sequential lamination require engineering review. The datasheet does not certify an Any-Layer HDI stackup.
QFPCB can provide stackup impedance simulation and technical review for multilayer, hybrid and approved HDI projects, including Any-Layer HDI when the conventional-material structure passes review. Because the published Dk is a 1GHz typical value, an impedance-control PCB still requires pressed dielectric thickness, glass/resin construction, copper and trace geometry.
PCB engineer Alan has more than 10 years of PCB CAM engineering experience. Send your ST115G stackup and thermal constraints to [email protected]. This support does not imply an unreviewed tolerance, named software, test coverage or first-pass guarantee.
When ST115G Is the Wrong Material Choice
Do not specify ST115G only because “higher thermal conductivity is better.” A thermally mild board may not justify its material and tooling implications. A board whose limiting resistance is the component package, thermal interface, enclosure or airflow may gain little from changing laminate alone.
Likewise, ST115G is not automatically the right choice for low-loss channels, a metal-backed heat path, extreme electrical isolation or customer-approved automotive material lists. Compare the actual requirement with alternatives such as Shengyi S1000H and keep substitutions under written design-owner approval.
Files Needed for an ST115G PCB Quote
- Gerber, ODB++ or IPC-2581 data and NC drill files
- Layer order, finished thickness and copper weight by layer
- Exact ST115G laminate and ST115GB prepreg construction
- Heat-source locations, loss estimates and thermal acceptance criteria
- Copper areas, thermal vias, exposed pads and interface requirements
- Finished-hole sizes, via types, aspect ratios and HDI layer pairs
- Impedance table, reference layers and requested tolerance
- Lead-free assembly profile, reflow count and rework exposure
- Halogen-free, CTI, flammability, traceability and certificate requirements
- Permitted substitutions, prototype quantity and production quantity
These inputs let QFPCB separate laminate data from finished-board performance. They also prevent a quotation from assuming that a supplier conductivity value guarantees junction temperature, that every ST115GB construction is stocked or that ordinary FR-4 drill parameters can be reused unchanged.
Frequently Asked Questions
What is the thermal conductivity of Shengyi ST115G?
Shengyi publishes typical values of 1.6 W/(m·K) by ASTM D5470 and 2.0 W/(m·K) by ASTM E1461. Always keep the test method with the number. Neither result directly specifies finished-PCB thermal resistance, which also depends on copper, vias, thickness, interfaces, cooling and the complete assembly.
What are the Tg and Td values of ST115G?
The official typical Tg values are 170°C by DSC and 175°C by DMA, while Td is 410°C at 5% weight loss by TGA. These measurements answer different questions. They do not define a continuous operating temperature or approve a particular reflow profile without board-level review.
Is ST115G halogen-free and high CTI?
Yes. Shengyi describes ST115G as halogen-free and reports CTI PLC 0 under IEC 60112. The finished PCB still needs compliance review because solder mask, inks, adhesives and assembly materials may have separate declarations. CTI also does not replace creepage, clearance and end-product safety requirements.
Is ST115G the same as a metal-core PCB material?
No. ST115G is a thermally conductive glass-reinforced laminate used in laminated PCB structures. A metal-core board adds an aluminum or copper base and a different dielectric heat path. Compare complete thermal resistance, routing, plated-hole needs, isolation, mechanics and manufacturing constraints rather than conductivity alone.
Can ST115G be used for HDI or Any-Layer HDI?
It may be evaluated for a reviewed rigid HDI construction, but approval is project-specific. Filler content, laser-via behavior, thin dielectric selection, copper filling and sequential lamination matter. Neither the TDS nor the material name qualifies an Any-Layer HDI stackup or guarantees its reliability.
Why does ST115G require different drilling parameters?
Its inorganic filler makes the laminate harder and increases tool wear. Shengyi recommends reducing infeed about 5-10% from high-Tg FR-4 starting settings, controlling drill hit count and using coated drills. Final speed, feed, stack height and tool life must be optimized for the actual construction.
What is the difference between ST115G and ST115GB?
ST115G identifies the copper-clad laminate, while ST115GB is the bonding prepreg. The prepreg is listed in 1080, 106 and 1027 constructions with different resin contents and cured thicknesses. A multilayer drawing should distinguish laminate cores from bonding layers and define substitution approval.
Is ST115G suitable for lead-free assembly?
Yes. Shengyi positions ST115G for lead-free processing and publishes T288 above 30 minutes plus thermal-stress performance above 30 minutes at 288°C. These are typical material results, not approval of every board or reflow cycle. Confirm moisture handling, board mass, copper balance and assembly exposure.
Request an ST115G Material and Thermal Stackup Review
Send QFPCB your fabrication files, ST115G/ST115GB callout, copper, vias, impedance table, heat-source map, assembly profile and quantity. We will review material availability, heat-flow assumptions and manufacturing inputs before quotation. Do not freeze the stackup from conductivity alone.
Official sources: Shengyi ST115G/ST115GB datasheet, document CN-TDS-2009-04-ST115G-ST115GB, and Shengyi processing guidelines, document CN-PG-1912-01-ST115G-ST115GB.
