Engineering resources
What controlled-flow prepreg is intended to control
Controlled-flow prepreg is selected because resin movement matters to the geometry of the finished assembly. Arlon EMD describes low-flow materials for rigid-flex bonding and heat-sink attachment, where resin must not spread excessively into openings or flexible regions. The design task is to define where movement is acceptable and how the resulting bond will be checked.
Turn “low flow” into a drawing requirement
Begin with a section through the transition, not only a material code. Show the rigid edge, flex opening, coverlay, bonding layer and any device or heat-sink clearance. Name the functional region that must remain free. State whether an intrusion dimension is measured from a routed edge, a copper feature or another datum.
The material designation should identify the intended bonding grade and its role. The manufacturer’s application guidance distinguishes different resin systems and product choices. It does not provide blanket approval of an arbitrary drawing. Avoid replacing a bondline review with the phrase “use no-flow prepreg.”
Example: allocate the clearance before selecting a limit
Hypothetical dimensional exercise. A rigid edge is nominally 1.20 mm from a region that must remain unobstructed. The team provisionally allocates 0.15 mm to edge-location uncertainty and 0.20 mm to an assembly positioning allowance. The remaining geometric budget is 1.20 − 0.15 − 0.20 = 0.85 mm.
That 0.85 mm is a budget to review, not an allowable resin-flow specification. It has not accounted for all manufacturing variation, the bond geometry or the inspection method. If the agreed intrusion allowance consumes the full remainder, the design has no explicit reserve. A better next action is to review the cross-section with the fabricator and define a measurable requirement supported by process evidence.
| Feature | Record on the drawing | Review evidence |
|---|---|---|
| Functional opening | Datum and required free envelope | Assembly clearance check |
| Bond region | Material, extent and thickness definition | Proposed construction |
| Transition | Coverlay and rigid-edge relationship | Section drawing and agreed inspection |
| Resin intrusion | Measurement direction and limit | Representative sample or agreed process qualification |
Inspect the actual requirement
Agree whether the critical boundary remains visible after processing. If it becomes concealed, plan suitable witness features or sectioning before ordering production. A photograph of one accessible edge cannot establish every internal bond region.
Record handling and processing requirements from the current grade-specific documents. Avoid copying a temperature or pressure from a different low-flow product. Keep the intended construction, material documentation and acceptance plan together. Start with the low-flow material directory, then review the complete manufacturing handoff.
Discuss your fabrication package
Submit project requirements and fabrication files for review. Material suitability, availability and commercial terms require project-specific confirmation.
Sources and scope
Manufacturer references checked 9 October 2026. Examples and review worksheets are original editorial guidance, not approved process instructions. Historical reference documents are used for fundamentals, not current product availability.