PCB Laminate FR-4 vs. Stainless Steel 303

Compare PCB Laminate FR-4 vs. Stainless Steel 303 strength, stiffness, weight and thermal properties.

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Mechanical
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Yield strength	not given (tensile used)	275MPasourceOutokumpu typical (product P = hot rolled plate, transverse)
Ultimate tensile strength	246–385MPasourcetypical, in-plane: cross direction .. length direction (ASTM D3039)	585MPasourceOutokumpu typical
Flexural strength	531–621MPasourcetypical: cross direction .. length direction (IPC-TM-650 2.4.4B)	not sourced
Elongation at break	not sourced	35%sourceOutokumpu typical, A5
Young's modulus (stiffness)	21.9–25.8GPasourcetypical, in-plane: cross direction .. length direction (ASTM D790-15e2)	200GPasourceat RT (Table 12)
Density	1,920kg/m³sourcetypical, 50% resin content; another FR-4 producer: Park Nelco N4000-6 (high-Tg multifunctional epoxy), not Isola 370HR	7,900kg/m³sourceat RT
Strength to weight	164kN·m/kg4.72x higher	34.8kN·m/kg
Stiffness to weight	12.4MN·m/kg	25.3MN·m/kg2.04x higher
Poisson's ratio	0.171–0.177sourcetypical, in-plane: cross direction .. length direction	0.3sourcedesign value (structural stainless steels)
Shear modulus	10.2GPa	76.9GPa7.57x stiffer in shear
Bulk modulus	12.2GPa	167GPa
Speed of sound	3,525m/s	5,032m/s
Thermal
Thermal conductivity	0.4W/m·Ksourcetypical (ASTM E1952); direction not stated by the sheet	15W/m·Ksourceat RT
Thermal expansion	13–14µm/m·Ksourcetypical, in-plane X/Y-axis, below Tg (IPC-TM-650 2.4.24C)	16µm/m·Ksourcemean, 20–100 °C
100 mm part over a 50 °C swing	67.5µm growth19% less	80µm growth
Specific heat	1,200–1,400J/kg·Ksourcetypical (ASTM E1461); another FR-4 producer: Park Nelco N4000-6 (high-Tg multifunctional epoxy), not Isola 370HR	500J/kg·Ksourceat RT
Heats up and cools (diffusivity)	0.16mm²/s	3.8mm²/s23.7x faster
Thermal shock resistance	324W/m	902W/m2.79x more resistant
Glass transition	180°Csourcetypical, DSC (IPC-TM-650 2.4.25C)	not sourced
Max service temperature	130°CsourceUL Relative Thermal Index (UL 796)	871°Csourcecontinuous, scaling limit
Values for	Isola 370HR FR-4 laminate (Polyclad PCL-FR-370HR, 180 C Tg multifunctional epoxy, E-glass fabric), copper removed; Isola data sheet Revision C, last updated April 15, 2021. Woven-glass laminate: the sheet gives in-plane values per weave direction (length / cross) and the Z-axis CTE separately; the solver is isotropic per material.	1.4305 / UNS S30300, Outokumpu typical values (hot rolled, solution annealed) from 'Steel Grades, Properties and Global Standards'; max service from Carpenter CarTech 303 datasheet

Every value links to the document that states it. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.

Questions

Is PCB Laminate FR-4 stronger than Stainless Steel 303?

PCB Laminate FR-4 is stronger: its tensile strength is 315 MPa against yield strength 275 MPa for Stainless Steel 303 (15%).

Which is lighter, PCB Laminate FR-4 or Stainless Steel 303?

PCB Laminate FR-4 is lighter: 1,920 kg/m³ against 7,900 kg/m³ for Stainless Steel 303.

Which is stiffer, PCB Laminate FR-4 or Stainless Steel 303?

Stainless Steel 303 is stiffer: Young's modulus 200 GPa against 23.9 GPa for PCB Laminate FR-4, so the same part in Stainless Steel 303 deflects less under the same load.

Which is lighter for the same job, PCB Laminate FR-4 or Stainless Steel 303?

For the same stiffness or strength: PCB Laminate FR-4 is lighter for a stiff beam (bending), stiff panel or plate, strong rod or tie, strong beam, strong panel or plate; Stainless Steel 303 is lighter for a stiff rod or tie (tension).

Part that must be	PCB Laminate FR-4	Stainless Steel 303
Stiff rod or tie (tension)	2.04x heavier	lighter
Stiff beam (bending)	lighter	42% heavier
Stiff panel or plate	lighter	2.03x heavier
Strong rod or tie	lighter	4.72x heavier
Strong beam	lighter	4.51x heavier
Strong panel or plate	lighter	4.41x heavier

For the same stiffness or strength, mass scales with density over stiffness (or strength) raised to a power set by how the part is loaded: 1 for a rod in tension, 1/2 for a beam in bending, 1/3 for a panel (the standard material-selection indices).

Which conducts heat better, PCB Laminate FR-4 or Stainless Steel 303?

Stainless Steel 303 conducts heat better: 15 W/m·K against 0.4 W/m·K for PCB Laminate FR-4.

Which expands less with temperature?

PCB Laminate FR-4 expands less: 13.5 µm/m·K against 16 µm/m·K for Stainless Steel 303.

Among 72 materials

Stiffness against density

Strength against density