PCB Board FR-4, 2 copper planes vs. Plastic PBT GF30

Compare PCB Board FR-4, 2 copper planes vs. Plastic PBT GF30 strength, stiffness, weight and thermal properties.

PCB Board FR-4, 2 copper planesComposite

Plastic PBT GF30Bulk polymer (molded or machined)

Mechanical	PCB Board FR-4, 2 copper planes	Plastic PBT GF30
Yield strength	not given (tensile used)	not given (tensile used)
Ultimate tensile strength	the bare laminate's246–385MPa1	stress at break140MPa2
Flexural strength	not sourced	210MPa2
Elongation at break	not sourced	strain at break3%2
Young's modulus (stiffness)	the bare laminate's21.9–25.8GPa1	9.8GPa2
Density	not sourced	1,530kg/m³2
Strength to weight	not sourced	91.5kN·m/kg
Stiffness to weight	not sourced	6.41MN·m/kg
Poisson's ratio	the bare laminate's0.171–0.1771	not sourced
Shear modulus	10.2GPa	not sourced
Bulk modulus	12.2GPa	not sourced
Speed of sound	not sourced	2,531m/s

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	PCB Board FR-4, 2 copper planes	Plastic PBT GF30
Thermal conductivity	not sourced	0.27W/m·K2
Thermal expansion	the bare laminate's13–14µm/m·K1	longitudinal25µm/m·K2
100 mm part over a 50 °C swing	67.5µm growth1.85x less	125µm growth
Specific heat	not sourced	1,050J/kg·K2
Heats up and cools (diffusivity)	not sourced	0.168mm²/s
Thermal shock resistance	not sourced	not sourced
Melting point	not sourced	DSC223°C2
Max service temperature	not sourced	HDT 1.8 MPa205°C2

Thermal conductivity against densityHigher and further left: spreads more heat for its weight

Thermal expansion against thermal conductivityLower and further right: warps less when heated

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Sources2 documents: Isola, BASF

PCB Board FR-4, 2 copper planes: A whole circuit board read as one orthotropic plate: the JEDEC high-K thermal test board (JESD51-7, "2s2p"), 0.062 in (1.575 mm) thick with two internal solid copper planes 0.0014 in (1 oz) thick, as Texas Instruments SZZA017A Table 1 gives it. Copper C110 and the Isola 370HR laminate from this library; the layers conduct in parallel along the board and in series through it (boardStackup.ts). Its two 0.0028 in trace layers cover little of the board and are left out; vias are ignored. Mechanical values are the bare laminate's.
Plastic PBT GF30: BASF Ultradur B 4300 G6 (PBT, 30% glass fibre), injection moulding grade; product information sheet 09/2026, typical values for uncoloured product at 23 °C.

1
370HR Laminate and Prepreg Data SheetIsolaarchived copyPCB Board FR-4, 2 copper planes · Ultimate tensile strength: the bare laminate's (fr4-370hr), in-plane: cross direction .. length direction (ASTM D3039)PCB Board FR-4, 2 copper planes · Young's modulus (stiffness): the bare laminate's (fr4-370hr), in-plane: cross direction .. length direction (ASTM D790-15e2); the copper planes are left outPCB Board FR-4, 2 copper planes · Poisson's ratio: the bare laminate's (fr4-370hr), in-plane: cross direction .. length directionPCB Board FR-4, 2 copper planes · Thermal expansion: the bare laminate's (fr4-370hr), in-plane X/Y-axis, below Tg (IPC-TM-650 2.4.24C)
2
Ultradur B 4300 G6 Product InformationBASFPlastic PBT GF30 · Ultimate tensile strength: stress at break, 23 °CPlastic PBT GF30 · Flexural strength: typical, 23 °CPlastic PBT GF30 · Elongation at break: strain at break, 23 °CPlastic PBT GF30 · Young's modulus (stiffness): typical, 23 °CPlastic PBT GF30 · Density: typicalPlastic PBT GF30 · Thermal conductivity: typical (DIN 52612-1)Plastic PBT GF30 · Thermal expansion: longitudinal (flow), mean 23-55 °CPlastic PBT GF30 · Specific heat: typical, 23 °CPlastic PBT GF30 · Melting point: DSC (ISO 11357)Plastic PBT GF30 · Max service temperature: HDT 1.8 MPa

Each number points to the document that states it, with the exact basis. Values without a number are computed from the sourced ones. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.

Questions

Mechanical

Is PCB Board FR-4, 2 copper planes stronger than Plastic PBT GF30?

PCB Board FR-4, 2 copper planes is stronger: its tensile strength is 315 MPa against 140 MPa for Plastic PBT GF30 (2.25x).

Which is stiffer, PCB Board FR-4, 2 copper planes or Plastic PBT GF30?

PCB Board FR-4, 2 copper planes is stiffer: Young's modulus 23.9 GPa against 9.8 GPa for Plastic PBT GF30, so the same part in PCB Board FR-4, 2 copper planes deflects less under the same load.

Thermal

Which expands less with temperature?

PCB Board FR-4, 2 copper planes expands less: 13.5 µm/m·K against 25 µm/m·K for Plastic PBT GF30.