RO4350B / MATERIAL PURCHASE TO FABRICATION DRAWING
RO4350B fabrication drawing notes should identify the exact laminate construction, dielectric thickness without copper, starting foil on each side and separately agreed finished-board requirements. A note reading “RO4350B, 0.5 mm, 1 oz” leaves several purchasing and inspection decisions unresolved. Does the thickness describe dielectric or the complete board? Does the copper weight describe the laminate as supplied or the plated conductor?
This guide resolves that specific handoff with a dimensional example, a material-note template and a supplier-response checklist. It complements the broader Rogers RO4350B PCB design and manufacturing guide. The example is a fictional two-layer RF coupon, not a released board design or evidence of available stock.
1. Define what the material line actually buys
Use the manufacturer’s name, grade and construction option together. State whether the requested laminate uses conventional electrodeposited copper or a specified LoPro construction. Identify the corresponding core in the stackup, rather than applying one material name indiscriminately to a multilayer board.
A useful material table separates four records: purchased laminate, bonding material where needed, finished copper and finished assembly thickness. Purchasing can then ask about the actual laminate configuration while CAM and inspection work from the finished-board drawing. One dimension cannot perform all four roles.
For the example, designate the dielectric between L1 and L2 as core C1. Request Rogers RO4350B with conventional ED foil, a nominal 0.020-inch dielectric and 1 oz starting foil on each side. Keep the inch dimension controlling in this illustrative purchase record; provide exact metric conversions for calculation. Confirm the supplier’s product designation before ordering.
The Rogers product selector, publication 92-601, revision code 1676 101525.200, lists RO4350B dielectric thickness without cladding as 0.020 inch ±0.0015 inch, with 1 oz foil represented as 35 µm. Its separate RO4350B LoPro entry lists 0.0207 inch ±0.0015 inch. These are catalog construction references, not a supplier inventory confirmation.
2. Calculate a thickness budget before specifying a finished dimension
Convert the conventional core example using exactly 25.4 millimeters per inch. Let h be the dielectric thickness without copper, and t1 and t2 the nominal starting foil thicknesses. At a location clad on both sides, the simple incoming-material budget is:
h = 0.020 × 25.4 = 0.508 mm
t1 = t2 = 0.035 mm
Tnominal clad = h + t1 + t2 = 0.578 mm
This calculated 0.578 mm is neither a guaranteed delivered thickness nor the finished PCB thickness. It excludes foil tolerances, copper added or removed during processing, final finish, mask and measurement-location effects. Patterned copper also means that a caliper reading depends on where the jaws contact the board.
The published dielectric tolerance converts to ±0.0381 mm, or ±7.5% of the nominal dielectric value. The dielectric-only interval is 0.4699–0.5461 mm. Holding both foils artificially fixed at 35 µm gives a calculated clad interval of 0.5399–0.6161 mm. This is a sensitivity exercise: do not present its endpoints as a complete laminate or board acceptance specification.
If a connector or housing needs a finished thickness limit, state that requirement separately and identify the measurement region. Ask the fabricator whether the proposed material and process can meet it. If not, resolve the mechanical constraint or investigate a different approved construction before ordering. A nominal core size should not silently become a tighter finished-board promise.
3. Treat a foil change as a construction change
“1 oz copper” specifies an amount, not a complete interface description. Retain the foil type, treatment and supplier construction identity along with its nominal weight. Also distinguish starting foil from the final conductor thickness used in a transmission-line model.
Rogers’ Copper Foils for High Frequency Materials, publication 92-243, revision code 1530 081826, describes reverse-treated foil and the bond-enhancement layer associated with LoPro copper. Its roughness discussion distinguishes measurement conventions and foil surfaces. Accordingly, a bare roughness number without a metric, method and surface identity is an incomplete modeling input.
For the catalog examples above, 0.0207 minus 0.0200 inch equals 0.0007 inch, or 17.78 µm. Do not add that difference again to a quoted LoPro dielectric dimension that already includes its construction. Ask the supplier what the stated thickness includes and use the approved stackup definition in the model. The comparison does not imply that changing foil always changes thickness by the same amount.
A proposal to replace conventional ED with LoPro may deserve investigation, but it needs a recorded electrical and purchasing decision. Conversely, “same copper weight” is not sufficient grounds to replace a requested low-profile construction with an ordinary foil. Keep each option identifiable while reviewing dimensions, modeling assumptions and qualification requirements.
4. Keep material characterization separate from board acceptance
The RO4000 datasheet, publication 92-004, revision 1592 080322, page 3, reports RO4350B process Dk as 3.48 ±0.05 at 10 GHz and 23°C using clamped stripline. Design Dk is listed separately as 3.66 over 8–40 GHz using differential phase length. Its 4-mil process-Dk exception is 3.33 ±0.05; that exception is not the value for this 20-mil example.
Do not write “finished board Dk = 3.66 ±0.05.” That combines two differently characterized quantities. Choose the model input appropriate to the construction and retain its source. Define finished-line acceptance through an agreed structure, target, tolerance and measurement method. A process-Dk range does not automatically become an impedance tolerance.
The same datasheet warns that RO4350B LoPro does not share the standard laminate’s UL designation. Where a product requires a flammability qualification, obtain the applicable construction-specific evidence rather than copying a family rating. The Dk and Df comparison resource can organize references, but cannot establish compliance for your purchased lot or finished assembly.
5. Write a material-specific RFQ note with visible open items
The following is original sample wording for a quotation drawing. It deliberately requires a supplier response before release. It does not prescribe a fabrication process or claim that the proposed combination satisfies an RF circuit.
Core C1, L1–L2: Rogers RO4350B, conventional ED copper construction. Requested dielectric thickness excluding copper: 0.020 inch nominal. Requested starting foil: 1 oz per side. Supplier shall identify the offered laminate configuration, applicable dielectric tolerance and material documentation. Submit proposed finished copper and finished-board thickness limits with their inspection basis. LoPro, alternate foil, alternate thickness or alternate grade requires written design approval. This material note remains FOR QUOTATION until the construction and acceptance record is completed.
For a multilayer design, name every bonding product separately. The RO4000 processing guide, publication 92-433, revision 1526 090221, points to the chosen adhesive system for bonding parameters and recommends tracking material lots through processing and delivery. A RO4350B core designation does not identify the adhesive or its pressed thickness.
Use the broader material construction qualification worksheet when comparing another grade. Here the decision is narrower: make the selected RO4350B purchase description agree with the model, drawing and incoming evidence.
Connect the specification to a budget: use the RF PCB cost planning tool only with clearly identified assumptions. Put the core, foil and open acceptance items in its project-notes field, then copy the summary. Its demonstration rates do not price a verified RO4350B construction. Compare supplier offers only after confirming that they describe the same build.
6. Reconcile the supplier response field by field
| Record | Required response | Decision owner |
|---|---|---|
| Laminate identity | Exact grade, construction option, foil and supplier designation. | Purchasing with design review. |
| Dimensions | Dielectric tolerance; finished copper and board limits; measurement basis. | Layout, mechanical and fabrication teams. |
| Electrical model | Geometry, material model, source conditions and any changed assumptions. | RF design owner. |
| Acceptance evidence | Material documentation, lot traceability and agreed inspection/test outputs. | Quality and project owner. |
A certificate identifying a laminate lot answers an identity question; it does not measure a connector’s return loss. Likewise, an impedance coupon cannot prove which procurement option was ordered without traceability to the build. Link each record to the relevant requirement instead of treating one document as universal evidence.
7. Complete a compact release checklist
- Mark core C1 and its layer relationship on the actual stackup.
- Confirm controlling units and whether each thickness includes copper, mask or finish.
- Record the accepted foil construction and finished conductor definition.
- Resolve any mismatch between the offered material and the electrical model.
- Agree lot documentation, inspection locations, acceptance limits and report scope.
- Remove unresolved alternatives from the released package; retain their review history separately.
For repeat production, reference the approved construction record as well as the board revision. If availability prompts a new proposal, identify what changed. A familiar material name is insufficient evidence that the original design assumptions remain intact.
Request a construction-specific RO4350B quote
Send the exact grade and foil option, dielectric thickness, stackup, quantity and fabrication revision. Include finished thickness constraints, copper requirements, controlled RF structures and acceptance evidence needed. Flag unresolved choices so engineering and purchasing can evaluate one consistent proposal.
Request a construction-specific RO4350B quote
Engineering references checked 11 October 2026. Document revision codes are identified beside the links. Calculations and diagrams are original illustrative work, not measurements, stock statements or production acceptance limits. Confirm the applicable supplier documents before release.
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