Choosing the right laminate is rarely about a single number. Signal speed, thermal reliability, mechanical durability and manufacturability all come from a small set of material properties. This page is the plain-English reference our engineering team uses with new customers.
Electrical properties
| Property | What it means | Why it matters | Impact on the PCB |
|---|---|---|---|
| Dielectric Constant (Dk) | How the dielectric stores electrical energy | Sets signal propagation speed and impedance | Lower & more stable Dk → faster signals, tighter impedance control |
| Dissipation Factor (Df) | Energy lost as heat in the dielectric | Critical for high-speed and RF designs | Lower Df → less attenuation over long traces |
| Electrical Strength | Maximum voltage the material can withstand | Determines insulation reliability | Higher value → less risk of dielectric breakdown |
| Volume Resistivity | Resistance through the bulk of the material | Insulating capability layer-to-layer | Higher → better isolation between planes / nets |
| Surface Resistivity | Resistance to current flow on the surface | Prevents leakage between adjacent features | Higher → better high-impedance / sensor performance |
Thermal & reliability properties
| Property | What it means | Why it matters | Impact on the PCB |
|---|---|---|---|
| Thermal Conductivity | Ability to transfer heat | Drives how well heat is dissipated | Higher → cooler junctions, better thermal management |
| Glass Transition Temperature (Tg) | Temperature where the resin softens | Indicates thermal reliability headroom | Higher Tg → survives lead-free reflow & harsh environments |
| Decomposition Temperature (Td) | Where the material chemically degrades | Limits exposure during assembly & rework | Higher Td → more reflow cycles without damage |
| Coefficient of Thermal Expansion (CTE) | How much it expands with temperature | Affects via barrels and solder joints | Lower CTE → less PTH cracking and pad fatigue |
| Moisture Absorption | Water absorbed from ambient air | Changes Dk and risks delamination at reflow | Lower → more stable electrical & long-term reliability |
Mechanical & manufacturability
| Property | What it means | Why it matters | Impact on the PCB |
|---|---|---|---|
| Mechanical Strength | Resistance to bending and stress | Affects durability and handling | Higher → tougher boards, less in-process damage |
| Flexibility | Ability to bend without damage | Defining property for flex / rigid-flex | Higher flex life → dynamic-bend applications |
| Flammability Rating | UL94 burn classification | Safety / regulatory compliance | UL94 V-0 is the standard target for most products |
| Copper Adhesion (peel strength) | Bond strength of copper to substrate | Trace and pad reliability | Higher → less delamination during thermal cycling |
| Thickness Tolerance | Variation in laminate thickness | Stack-up and impedance accuracy | Tighter → predictable controlled-impedance results |
| Glass Weave Style | Fiber bundle structure (1080, 2116, 3313, etc.) | Influences fiber-weave-effect skew | Optimized weave → cleaner high-speed eyes |
| Chemical Resistance | Resistance to process chemistries | Affects yield and durability | Higher → cleaner inner-layer image and better plating |
Rule of thumb
Always compare Dk and Df at the same frequency and the same test method. A “lower Dk” at 1 GHz is not necessarily lower at 28 GHz, and stripline / IPC TM-650 numbers are not directly comparable to vendor design-Dk values.
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