Customer-provided drawings are a critical part of the manufacturing package for a flex circuit manufacturer. While the gerber files give a flex circuit manufacturer the details for the actual copper circuit, via holes, layers and outline of the circuit, the drawing specifies customer-acceptance criteria, inspection criteria, electrical parameters etc.
Below is an example of a list of potential drawing notations that a flex circuit manufacturer would accept. Included are many of the IPC specifications that should be referenced.
- Represents a critical dimension
- Fabrication of this flex shall be in conformance with the following specifications: IPC-6013 class 2, IPC-A-610 class 2
- Dimensions are in inches and are ±.010 unless otherwise noted
- Flame class to be UL 94v-0 and must meet requirements of UL 796
- See PFC gerber package for hole chart and plating specs.
- See PFC gerber package for conductor geometry
- See PFC gerber package for stiffener tool-chart geometry
- Conductors: minimum trace width = .0056″, minimum space = .0067″
- Coverfilm/soldermask: must be in accordance with IPC-6013 class 2
- Finish: immersion gold (enig) per IPC-4552
- Silkscreen: white non-conductive ink. No ink to appear on exposed copper such as plated through hole pads and surface mount lands
- Electrical test:
Tested to standard pfc-wi-136
100% isolation and continuity test required for every board
100% hi-pot test required at 250v
Maximum connector to connector to be 10 Ohms
Minimum pin to pin isolation to be 5.0 mega Ohms
- Impedance: boards are “build to stack”. Impedance requirements for each layer are shown below for reference.
- Layer stackup: layer name; type; thickness; width; impedance
- FR4 TG: minimum glass transition temperature (TG) of 170°c
- RoHS: all materials must be compliant with the european union RoHS directive, 2002/95/EC
- PFC lot code: contain PFC logo with UL marking and WW-YY lot#
- Parts to be 100% electrically tested for continuity per PFC-WI-136
- Parts to be RoHS compliant
- Parts to be built/inspected per IPC-a-610 and IPC 6013 class 2
- Solder type: no clean lead-free
- Packaging: all assemblies to be packaged per PFC-WI-164
Flex circuit material stack-up
In addition to drawing notes, PFC requests that the material stack-up is created for each circuit. The stack up designates specific material part numbers along with the overall thickness of the circuit. Below is an example of the stack-up from a two layer circuit with an FR-4 stiffener.