IMS / MCPCB SPECIFICATIONS
Metal Core PCB Capabilities: IMS Dielectric, Thickness and Tolerances
These are the fabrication limits APTPCB works to for metal core PCBs (IMS boards): dielectric range, base and finished thickness, trace and space by copper weight, drill, finish and outline tolerances. Use them to check a layout before release. To choose between aluminum and copper base, or to prepare a quote, go to the metal core PCB manufacturer page.
Get an Instant Quote
What are the metal core PCB capabilities at APTPCB?
Standard metal core builds are 1–2 circuit layers on an aluminum (5052/6061) or copper (C11000) base, with a 75–200 µm thermally conductive dielectric, 0.5–4 oz finished copper and a finished thickness of 0.5–4.6 mm. Builds up to 4 layers, iron bases and thicknesses outside these windows are reviewed case by case.
Limits interact. A thinner dielectric lowers thermal resistance but reduces the voltage it can hold; heavier copper widens the minimum trace, space and annular ring. Check every row below against the same copper weight and board thickness, not against the best value in each row.
Selecting the base metal, pricing and lot documents are covered on the metal core PCB manufacturer page (aluminum vs copper MCPCB, RFQ checklist and price drivers). If MCPCB may not be the right structure, see high thermal conductivity PCB options.
IMS dielectric and metal base parameters
| Parameter | Aluminum base | Copper base | What to check |
|---|---|---|---|
| Base alloy | Al 5052 / 6061 | Cu C11000 | Alloy and temper on the drawing; iron base by review |
| Base thickness | 1.0–3.2 mm | 1.0–3.2 mm | Other gauges by review; sets stiffness and finished thickness |
| Dielectric thickness | 75–200 µm | 75–150 µm | Thinner lowers thermal resistance and lowers voltage margin |
| Dielectric thermal conductivity | 1.0–3.0 W/m·K | 3.0–8.0 W/m·K | Quote the material grade and test method, not only the W/m·K value |
| Dielectric breakdown | ≥ 3 kV | ≥ 3 kV | Material rating; finished-board withstand test is specified separately |
| Dielectric systems | TCLAD/Bergquist, Ventec, Arlon or approved equivalent | Premium IMS dielectric by grade | Substitutions need written approval |
| Flammability | UL 94V-0 | UL 94V-0 | Confirm the listing for the exact material |
| Base-side finish | Per drawing | Per drawing | Bare, anodized or passivated surface affects TIM contact |
Dielectric values are material ranges. The board-level thermal result depends on copper area, solder, TIM and mounting.
Metal core PCB fabrication tolerances by parameter
| Parameter | Standard Capability Range | Engineering Verification Condition |
|---|---|---|
| Layer count | 1–2 circuit layers standard; up to 4 by review | Metal position in the stack, hole isolation from the base and lamination sequence confirmed at DFM. |
| Metal substrate base | Aluminum (5052 / 6061) or copper (C11000); iron by review | Specify alloy, thickness, surface treatment and whether the base is electrically grounded. |
| Finished Board Thickness | 0.5–4.6 mm | Final thickness tolerance depends on metal base gauge, dielectric thickness, copper foil weight, and panel size. |
| Surface Finishes | Lead-free HASL, ENIG, OSP, Immersion Silver, Hard Gold | Selected according to SMT solderability, shelf-life, wire bonding, contact fingers, and environmental compliance. |
| Board Dimension Window | Min. 5.1 × 5.1 mm; max. 1,100 × 483 mm | Extra-long linear panels require panelization, CNC routing, bow and twist, and handling review. |
| Min Trace / Space @ 0.5 oz | 4 / 4 mil | Confirmed against copper foil finish, conductor topology, panel yield, and dielectric voltage breakdown limits. |
| Min Trace / Space @ 1 oz | 5 / 5 mil | Confirmed against finished copper thickness, etch compensation factors, and current density requirements. |
| Min Trace / Space @ 2 oz | 5 / 7 mil | Spacing rules expand proportionally with finished copper thickness and chemical etch factors. |
| Min Trace / Space @ 3 oz | 7 / 8 mil | Trace geometry subject to landing pad layout, spacing clearances, and local copper density. |
| Min Trace / Space @ 4 oz | 10 / 10 mil | Heavy copper conductors require expanded spacing clearances and multi-stage etching verification. |
| Min Annular Ring @ 0.5 oz | 4 mil | Correlated to finished hole diameter, drilling drill-wander tolerances, and metal core clearance. |
| Min Annular Ring @ 1 oz | 5 mil | Correlated to finished hole diameter, drilling registration, and core isolation clearances. |
| Min Annular Ring @ 2 oz | 7 mil | Correlated to drill registration, heavy copper etching tolerances, and finished hole size. |
| Min Annular Ring @ 3 oz | 10 mil | Correlated to heavy copper etch undercut, hole registration, and mechanical isolation. |
| Min Annular Ring @ 4 oz | 16 mil | Correlated to thick foil etch profiles, mechanical stability, and dielectric back-fill integrity. |
| Circuit Copper Weight | 0.5–4 oz finished | Distinguish clearly between starting base foil weight and post-plating finished copper weight. |
| Min Drill & Tolerances | 30 mil for 0.5–2.0 mm boards; 45 mil for 2.0–4.6 mm boards; PTH ±4 mil; NPTH ±3 mil | Validate finished hole diameter, metal core isolation margins, aspect ratio, and plating sequence. |
| Copper / Solder Plating (HASL) | Copper 20–35 µm; Tin 5–20 µm | Plating thickness window confirmed in traveler plating log and cross-section inspection. |
| Electroless Nickel Immersion Gold (ENIG) | Nickel 100–200 µin; Gold 2–4 µin | Coating thickness and XRF verification method confirmed to IPC-4552 specifications. |
| Hard Gold Plating | Nickel 100–200 µin; Gold 4–8 µin | Specify plated area, contact duty cycle, gold hardness (Knoop), and insertion life targets. |
| Gold Edge Fingers | Nickel 100–200 µin; Gold 5–15 µin | Specify chamfer angle (20°/30°/45°), finger tie-bar routing, and contact wear resistance. |
| Immersion Silver | 6–12 µin | Anti-tarnish packaging, controlled storage conditions, and assembly window confirmed at RFQ. |
| Organic Solderability Preservative (OSP) | Film thickness 8–20 µin | Thermal cycle compatibility and multi-reflow assembly pass requirements confirmed. |
| Gloss Solder Mask | Green, black, red, yellow, white, blue, or purple | Mask color affects optical reflectivity (critical for LED boards), inspection, and surface emissivity. |
| Matte Solder Mask | Matte green or matte black | Material selection and appearance criteria confirmed prior to production release. |
| Solder Mask Thickness | 0.2–1.6 mil over copper traces | Actual coverage depends on copper foil thickness, conductor edge profile, and measurement location. |
| Min Solder Mask Dam | Green 4 mil; other colors 5 mil | Confirmed against mask registration tolerances, copper weight, and SMD pitch geometry. |
| Plugged Via Diameter | 10–25 mil | Specify plugging resin, filling percentage (≥100%), surface planarization, and coverlay capping. |
| Silkscreen Legend | White or black | Selected for optimal optical contrast against solder mask color after SMT reflow cycles. |
| Silkscreen Resolution | Min line width 5 mil; min character height 24 mil | Confirmed against font style, line stroke weight, and component pad clearances. |
| Electrical Testing | Flying probe or dedicated bed-of-nails fixture per IPC-9252 | Define netlist reference, test voltage, continuity resistance thresholds, and isolation resistance limits. |
| CNC Outline Profiling Tolerance | ±5 mil | Confirmed against overall board dimensions, internal pocket radii, metal base alloy, and datums. |
| V-Scoring Tolerance | ±5 mil | Define residual web thickness, top/bottom score symmetry, break-out force, and burr allowances. |
| Min Milled Slot Width | 40 mil | End-mill diameter, milling depth through metal base, and tool clearance verified by CAM. |
| V-Score Angles | 15°, 20°, 30°, 45°, or 60° | Scoring angle and residual core thickness configured for manual or automated singulation. |
| Bow and Twist Flatness | Target ≤1.0% (≤0.75% for SMT automated assembly) | Criteria must specify board dimensions, test procedure per IPC-TM-650 2.4.22, and support constraints. |
| Quality Acceptance References | IPC-6012 and IPC-A-600 Class 2 / Class 3 (when specified) | Applicable performance class, inspection amendments, and custom acceptance limits stated in RFQ. |
Values are standard fabrication windows. Extreme values in different rows may not combine on one board; DFM review confirms the set for your stackup.
Metal core PCB DFM rules to check before layout release
| Design rule | Limit on this page | Why it matters on IMS |
|---|---|---|
| Plated holes near the base | Isolation clearance confirmed at DFM | A plated barrel that touches the metal base shorts the circuit to the plate. Thermal vias copied from FR-4 are not allowed by default. |
| Minimum drill | 30 mil (0.5–2.0 mm board); 45 mil (2.0–4.6 mm board) | Drilling through metal wears tools and raises burrs; small holes in thick boards are the first DFM flag. |
| Annular ring vs copper weight | 4 mil @ 0.5 oz up to 16 mil @ 4 oz | Heavier copper etches with more undercut, so the ring grows with weight. |
| Trace / space vs copper weight | 4/4 mil @ 0.5 oz up to 10/10 mil @ 4 oz | Use the row for the finished copper weight, not the starting foil. |
| Milled slots | Minimum 40 mil width | The end mill has to cut the metal base as well as the dielectric. |
| V-score | ±5 mil; 15°–60° angles | Residual web through the metal decides break-out force and edge burr. |
| Copper to board edge | Set at DFM for the working voltage | Routed metal edges are exposed; keep copper back far enough to hold creepage. |
| Flatness | Target ≤1.0% bow and twist (≤0.75% for automated SMT) | A bowed plate leaves air gaps at the heatsink and raises thermal resistance. |
Creepage, clearance and withstand voltage come from the product safety requirement; state them on the drawing so the dielectric and edge clearances can be checked.
What these metal core PCB specifications do not cover
The tables describe the bare board. They do not predict junction temperature, prove a safety rating for the finished product or replace system thermal testing; those depend on components, solder joints, TIM, heatsink, airflow and enclosure.
Combinations at the edge of several windows at once (for example 4 oz copper, minimum drill and maximum board size on one design) are confirmed only after DFM review of the actual files.
Metal core PCB capabilities FAQ
Can thermal vias go directly into the metal base of an MCPCB?
Not by default. A plated via that reaches an aluminum or copper base shorts the circuit to the plate. Multilayer IMS with insulated holes, or a local copper coin, needs its own stackup and DFM review.
What is the minimum trace and space on a metal core PCB?
4/4 mil at 0.5 oz finished copper, 5/5 mil at 1 oz, 5/7 mil at 2 oz, 7/8 mil at 3 oz and 10/10 mil at 4 oz. Use the value for the finished copper weight.
Can metal core PCBs have plated through-holes and more than one layer?
Yes. 1–2 circuit layers are standard, and builds up to 4 layers with plated holes are reviewed case by case. They need a defined stackup, pre-drilled and resin-filled clearances in the metal, and adequate annular rings.
How thick can the IMS dielectric be, and what does it change?
The standard range is 75–200 µm on aluminum and 75–150 µm on copper. Thinner dielectric lowers thermal resistance; thicker dielectric holds more voltage. The working voltage sets the lower limit.
What is the largest metal core PCB you can build?
Boards from 5.1 × 5.1 mm up to 1,100 × 483 mm. Long linear boards such as LED strips need a panel, routing and flatness review.
Which surface finishes are available on metal core PCBs?
Lead-free HASL, ENIG, OSP, immersion silver and hard gold, with green, white, black and other mask colors. White mask is common on LED boards for reflectivity.
Check your metal core PCB layout against these limits
Send the Gerber files and stackup. Engineering confirms which rows apply, flags any combination outside the window, and returns DFM comments with the quote.