吃瓜tv · Heavy-copper design review
5 oz copper PCB: follow the complete current path
Use about 175 ?m as a planning label, then check pad necks, etched geometry, lamination and inspection before committing a heavy-copper design.
Preliminary copper specifications and open manufacturing questions are welcome.
What is a 5 oz copper PCB?
A 5 oz copper PCB specifies approximately five ounces of copper per square foot on the named layers, often represented by about 175 ?m or 0.175 mm for planning. The designation is not the finished board thickness. It must also be identified as starting or finished copper, and as a nominal or minimum requirement, before it can serve as an unambiguous manufacturing instruction.
Five-ounce copper is considered for power distribution, converters, motor drives and other circuits where conductor loss or available routing area makes a heavier construction worth reviewing. It is not a universal current rating. A short pad neck, a plated hole or a connector can still limit the path even when a large conductor region is thick.
This page follows the complete current path through a 5 oz design. The broader heavy copper PCB guide compares the family of constructions. For adjacent options, the 4 oz geometry page focuses on etched cross-sections, while the 6 oz construction page develops mixed-copper stackup questions. Keep the decision tied to the actual design constraint.
Start at the connector and follow every restriction
Mark the outgoing and return path on the layout. Divide each into broad conductors, narrow escapes, transitions and interfaces. A large copper area is only useful if current can enter and leave it through suitable geometry. Review the region around the terminal, fuse, relay, shunt and power semiconductor, not only the middle of the polygon.
For a simple uniform rectangular segment, resistance is proportional to length divided by width and thickness. Two segments with the same length-to-width ratio and copper thickness have the same ideal DC resistance at the same temperature. A short narrow region can therefore contribute as much resistance as a much longer broad region.
Take an illustrative 175 ?m path containing 80 mm at 8 mm width, 10 mm at 1 mm width and another 10 mm at 8 mm width. Their length-to-width ratios are 10, 10 and 1.25 squares. The neck occupies 10% of the total path length but contributes about 47.1% of the simple series resistance. Widening only the broad sections does not remove that restriction.
Compare series loss contributions in the 5 oz path
Enter two to twenty segments as length in millimeters, finished width in millimeters and finished copper in micrometers. Keep them in physical order and describe that order in the source field. The model uses one conductor temperature and one DC current for all series segments. It adds electrical resistance and identifies both the largest total contribution and the largest resistance per unit length.
5 oz Copper Series Path Review
At 75°C and 20 A, the three-segment example gives approximately 2.467 mΩ total resistance, 49.34 mV drop and 0.987 W total copper loss. The main segment and neck each dissipate about 0.464 W in this model, but that loss is concentrated over very different lengths. The last segment contributes about 0.058 W. These are reproducible electrical calculations, not measured 吃瓜tv product results.
The distinction between total loss and loss per length matters. A long conductor can generate more total heat but spread it over more board area. A small neck may require closer thermal review even if another segment has a larger total wattage. Neither result alone identifies the hottest temperature; heat spreading, neighboring copper, mounting and airflow determine that outcome.
The model uses approximate copper resistivity of 17 × 10?? Ω·mm at 25°C with a 0.0039/°C coefficient, following the rectangular-trace method documented in (the guide uses 16.8 × 10?? Ω·m; this worksheet rounds resistivity to 17 × 10?? Ω·m). It excludes contacts, plated barrels, irregular current spreading and AC loss. Add those elements using an appropriate model or measurement before treating a path budget as complete.
Review finished traces, pad necks and plated transitions
The etching process must remove unwanted copper while preserving the specified conductor and gap. Heavy copper affects this task, so a fine-line rule borrowed from a standard board may not be applicable. Ask for the intended finished geometry and the fabricator's compensation approach. Do not manually add an arbitrary etch allowance and assume it will match the supplier's process.
Spacing has two separate roles. The manufacturing process must produce the gap, and the application must meet its electrical insulation requirement. A gap that can be etched is not automatically sufficient for operating voltage, contamination or safety constraints. Record the applicable product requirements and review clearances with the responsible designer.
Surface copper does not determine hole-wall copper. When current changes layers, define the plated structure, actual path length, holes, connection geometry and inspection scope. Multiple parallel holes may not share current equally if their connecting copper is asymmetric. A simple “amps per via” multiplier misses that interaction. For via-dominated power routes, the 10 oz transition guide provides a more specific discussion without requiring the entire board to use that copper weight.
Coordinate heavy power layers with signal layers
Not every layer needs 5 oz copper. A mixed construction may place heavier copper on the power layers while retaining lighter signal layers where routing and impedance need different geometry. This decision changes the stackup, resin requirements and fabrication route. It should be agreed before the signal layout is treated as final.
Spaces between heavy copper features must be filled by the intended insulating system. Copper coverage and its distribution influence the resin-flow problem; summing foil thicknesses is not a resin-fill calculation. The fabricator needs the actual artwork, material system and pressed-thickness target to assess the construction. A symmetric-looking drawing does not by itself prove flatness or adequate insulation.
Assembly planning also matters. Large copper areas can draw heat from solder joints, while isolated fine-pitch regions behave differently. Thermal relief decisions must balance electrical loss, soldering access and assembly method. Keep terminal soldering, selective processes and rework expectations with the assembly review. Do not solve a solderability problem by weakening a power connection without checking its electrical function.
Define evidence for the actual risk
The distinguish conductor definition, plated structures and structural integrity. Use the selected full standard and agreed product requirements to define acceptance; the public preview is not a replacement for its detailed clauses. Do not infer that a thicker foil automatically establishes a particular IPC class.
For a critical path, useful evidence can include finished geometry, relevant sections, electrical resistance and a controlled load test. Define locations and conditions so the results can be compared with the design. If a coupon is used, explain what it represents and what differences remain between the coupon and the real terminal region. An attractive cross-section photograph without traceability is not a release record.
The power-distribution photograph illustrates why terminals and board interfaces belong in the review. It is not identified as a 5 oz test article. For a new project, preserve the board revision, build record, connector arrangement, mounting and measurement points with the data. Those details make a later repeat order or change review more reliable.
Quote the manufacturing route, not only the ounce value
A 5 oz quotation should state which layers are heavy, the finished minimums, smallest conductor and gap, total stack thickness, hole structure, surface finish and acceptance plan. Cost depends on the combination. Material, imaging, etching, plating, lamination, panel utilization and verification can all contribute; the weight label alone cannot justify a universal price multiplier.
If the design is still flexible, request a comparison that changes only one meaningful assumption. For example, compare the current 5 oz route with a wider lighter-copper route while holding quantity, outline and acceptance scope constant. If the outline also changes, include panel utilization and system effects in the comparison rather than attributing the entire price difference to copper.
Open optional hardware budget and RFQ brief
5 oz PCB Budget and RFQ Brief
The optional budget brief uses your dated allowances and retains the construction context. Blank cost fields produce a technical request. It does not import FR-4 market rates or automatically quote a heavy-copper premium. For a firm manufacturing quotation, attach the actual files and name any incomplete specification so engineering can review it explicitly.
Before ordering a 5 oz PCB
Is 5 oz copper exactly 175 ?m?
It is a rounded planning conversion. Procurement and inspection need the applicable nominal or minimum finished value, its tolerance convention and its layer assignment. Ask for the finished requirement to be repeated in the accepted stackup so the order cannot be interpreted solely as a starting foil weight.
Does 5 oz copper carry five times the current of 1 oz?
No. Even if a conductor's cross-section changes by that ratio, temperature and allowable current do not follow the same simple proportional rule. treats conductor size, current and temperature together. The complete environment and current path must be evaluated.
Should I increase thickness or remove a neck-down?
Use the actual geometry to identify where resistance accumulates, then review the thermal and assembly constraints. Removing a local restriction may be more effective than thickening an already broad conductor. A neck can also be required by a package or terminal, in which case the interface itself needs attention.
Can I send a partial layout for review?
Yes. Include the current path, approximate outline, layer roles, expected current conditions and the main uncertainty. A full production release needs more detail, but an early review can identify whether a proposed 5 oz construction is the right question before additional layout work is committed.
Request a 5 oz Copper PCB review
Send the board revision, copper by layer, base or finished requirement, outline, quantity and test scope. Include the bottleneck or unresolved manufacturing question so the quote can address it.
Tool use is optional. Attach any downloaded brief manually; Contact does not automatically receive worksheet inputs. References reviewed September 2026. Illustrations are explanatory, and photographs are not process qualification records.