Heavy copper PCB

01

Size the copper for current and heat

Texas Instruments' motor-driver layout note (SLVA959B) treats copper thickness as a critical factor in PCB thermal performance. Taking 1 oz copper as 0.0035 cm thick, it calculates about 71.4 °C/W for a 1 cm × 1 cm copper plane joined laterally to a driver, and 35.7 °C/W for 2 oz (0.007 cm): doubling the thickness halves the thermal resistance. It recommends 1.5 or 2 oz copper where possible for motor drivers. [1]

TI's LMG5200 layout note (SNVA729A) gives conductor resistance as R = ρ × l ÷ A and notes that copper resistance varies linearly with temperature, doubling between 25 °C and 280 °C. [2]

Editorial calculation: taking TI's 1.7 µΩ·cm figure for pure copper, a 100 mm long, 10 mm wide trace has about 4.9 mΩ at 1 oz (0.0035 cm) and about 1.6 mΩ at 3 oz (assumed 0.0105 cm); at 20 A that is roughly 1.9 W versus 0.65 W of loss before any temperature rise. Ask the fabricator for finished, not base, copper thickness on each layer. [2] [1]

The laminate between the copper layers limits how that heat leaves. Isola's 370HR data sheet (Rev. C, 2021), a 180 °C Tg FR-4 epoxy system, lists standard copper weights of ½ to 2 oz (18 to 70 µm) with heavier copper available, a thermal conductivity of 0.4 W/m·K, a decomposition temperature of 340 °C, time to delamination of 60 minutes at 260 °C and 30 minutes at 288 °C, Z-axis expansion of 2.8% from 50 to 260 °C, Dk 4.04 at 2 GHz, UL 94 V-0 flammability and a relative thermal index of 130 °C. [3]

Editorial calculation: through a 0.1 mm dielectric layer at 0.4 W/m·K, a 1 cm × 1 cm area has a thermal resistance of about 2.5 °C/W (0.0001 m ÷ (0.4 × 0.0001 m²)), so heat from a heavy-copper trace crosses thin prepreg readily but spreads sideways mainly through the copper itself; and 2.8% Z expansion across a 2.4 mm board is about 67 µm, strain the plated vias in a thick-copper stack must take. [3]

Give the fabricator the layer count and finished copper weight per layer, currents per net and allowed temperature rise, board thickness and laminate (Tg), minimum trace width and spacing in heavy copper areas, via sizes and plating thickness, surface finish, solder mask, panel size, IPC class, test requirements and quantities.

02

Check via current and plated copper

Citing IPC-2152, TI's motor-driver note lists the current capacity of a single via on a 1 oz board for a 10 °C rise: 0.2 A at 6 mil, 0.55 A at 8 mil, 0.81 A at 10 mil, 0.84 A at 12 mil and 1.1 A at 16 mil diameter, and recommends multiple vias placed close to where current enters or leaves component pins. [1]

TI's GaN note states that plated copper has significantly higher resistivity than pure copper (6 versus 1.7 in its units), that vias use plated copper so enough of them are needed at high current, and that on a board plated once for both surface and holes the extra plating gives only about a 25% resistance reduction for a 2 oz board compared with a 1 oz board without plated copper. It also gives 0.75 A as a general maximum for a 12 mil via in 1 oz copper. [2]

Editorial calculation: carrying 20 A through 12 mil vias at TI's 0.84 A per via (10 °C rise, 1 oz) needs at least 20 ÷ 0.84 ≈ 24 vias; ask the fabricator what via plating thickness its heavy copper process gives. [1]

03

Compare what suppliers offer

Suppliers linked to this page list heavy or thick copper PCBs; each card links to the page reviewed.

Listings include heavy copper boards stated up to 20 oz, multilayer heavy copper boards and planar-winding PCBs.

04

Ask for minimum trace and space at your copper weight

PCB fabricator PCB Universe publishes its recommended minimum trace width and space on outer layers by copper weight, and states that heavy copper raises the minimum because of the increased risk of unintended short circuits. It treats 3 oz or more on internal or external layers as heavy copper, states capability up to 36 layers and 20 oz copper, and quotes boards of 3–20 oz individually. [4]

The fabricator says it can make smaller trace and space than this table at a higher price, asks for the board stack-up to confirm that the board thickness and copper weight can be achieved, and notes that heavy copper may need a thicker finished board, particularly where controlled dielectric is also required. [4]

Editorial calculation: 8 mil is about 0.20 mm and 24 mil about 0.61 mm, so going from 2 oz to 6 oz triples the minimum trace-plus-space pitch from 16 to 48 mil. Size high-current nets for current and temperature rise first, then check them against the fabricator's own table for each layer. [4] [1]

05

Trace the board construction

This is a functional reference built from the sources cited; it is not one fabricator's stack-up.

06

Fill the specification fields with values for your board

A heavy copper PCB quotation needs values for your board. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the fabricator.

07

Send the copper, current and stack-up data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Copper: [finished oz per layer]
Current: [A per net; temperature rise]
Vias: [size; count; plating]
Board: [layers; thickness; laminate; Tg]
Geometry: [min trace; spacing]
Build: [finish; mask; IPC class; quantity]

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