Inter-Layer Checks
Performing inter-layer checks allows the developer to check a range of locations in the rigid flex PCB design:
● Layer-to-layer checks to evaluate stack-up mask layers
● Coverlay to pad
● Mask to pad
● Rare-earth element to coverlay
● Bend area/line to support, component, pin, and using
● Voids, such as edge-to-edge spacing in areas such as the bend line to the component, the through to the bend line, and the stiffener to the bend location
● Inside areas, such as gold mask to coverlay, pin to coverlay, and stiffener sticky to stiffener
● Overlaps when 2 geometries overlay by a minimum or even more, such as soldermask overlay right into the transition area
Commonly, developers have actually had to do design guideline checks (DRCs) by hand, or create their very own software application to automate the procedure. There are likewise tools on the marketplace that support rigid flex PCB design, but they are not specifically extensive in terms of the breadth of inter-layer checks currently needed. An useful tool also should be able to deal with different design considerations, which we will outline in the next area.
Rigid Flex PCB Design Considerations
MCAD-ECAD Co-Design
All electronics have to match rooms, making MCAD-ECAD co-design a need. Nevertheless, rigid flex PCBs call for extra examination with the bending of the flex inside the room. The mechanical designer has to supply the bend area, bend line, and bend radius to the PCB developer, who have to produce and stick to numerous rules:
● Do not put vias in bend areas to prevent splitting the substrate gradually
● Do not place pads as well near to the bend area, as the pads can eventually peel
● Prevent overlapping bend areas with stiffeners, otherwise there could be peeling off or limitation of the full bend
● Stay clear of positioning stiffeners also near vias or pins to avoid shorting
Mechanical designers must additionally define the particular borders for zones, where the densities are different throughout the whole design framework. In return, mechanical engineers have to obtain additional information concerning layer structures and density for the areas, including above and below the leading and bottom layers to calculate precise thickness and accurate accident discovery before handing the design to PCB manufacturing. These layers include paste mask, coverlay, stiffeners, exterior copper, and various other materials that impact general height, thickness, and bend performance.
Element Positioning
Because of various developments, CAD tools can now smartly auto-drop parts as they are crossed rigid flex substratum borders. This capability gets rid of the tedious steps of moving the components to the surface layers. Yet, are the outcomes adequate? Most of the times, element plans used for flex areas will certainly vary from the ones used in rigid zones. As an example, padstacks for flex areas have the tendency to be longer to sustain the flexing activity of the material. For that reason, the CAD system ought to be able to “retarget” the package with the proper alternating icon for the particular technology area.
Interconnect
Directing flex vs. rigid normally comes down to one word: arcs. The nature of all geometry living in a flex PCB zone, whether it’s the board synopsis, teardrops, or directing, entails arcs and tapered changes. CAD tools should support system routing features to carry a bus throughout the flex while securing to the contour of the board outline. Line-width shifts must be tapered and all pin/via joints should be tear-dropped to lower tension at the solder joints. Developments in CAD tools over the years have actually resulted in a better capacity to push and push traces throughout the edit regulates. However, this has, for the most part, been a challenge with arc routes. Modification, also daily change, is a given in PCB design. However adding an additional signal to a routed bus construct ought to not need developers to delete routes followed by the team reroute.