Circuit diagramCustomer-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.

Flex notes

  1. Represents a critical dimension
  2. Fabrication of this flex shall be in conformance with the following specifications: IPC-6013 class 2, IPC-A-610 class 2
  3. Dimensions are in inches and are ±.010 unless otherwise noted
  4. Flame class to be UL 94v-0 and must meet requirements of UL 796
  5. See PFC gerber package for hole chart and plating specs.
  6. See PFC gerber package for conductor geometry
  7. See PFC gerber package for stiffener tool-chart geometry
  8. Conductors: minimum trace width = .0056″, minimum space = .0067″
  9. Coverfilm/soldermask: must be in accordance with IPC-6013 class 2
  10. Finish: immersion gold (enig) per IPC-4552
  11. Silkscreen: white non-conductive ink. No ink to appear on exposed copper such as plated through hole pads and surface mount lands
  12. 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
  13. Impedance: boards are “build to stack”. Impedance requirements for each layer are shown below for reference.
  14. Layer stackup: layer name; type; thickness; width; impedance
  15. FR4 TG: minimum glass transition temperature (TG) of 170°c
  16. RoHS: all materials must be compliant with the european union RoHS directive, 2002/95/EC
  17. PFC lot code: contain PFC logo with UL marking and WW-YY lot#

Assembly notes

  1. Parts to be 100% electrically tested for continuity per PFC-WI-136
  2. Parts to be RoHS compliant
  3. Parts to be built/inspected per IPC-a-610 and IPC 6013 class 2
  4. Solder type: no clean lead-free
  5. 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.

flex circuit material stack up flex circuit material stack up legend