Integrity wins the world, quality creates the future!
Shenzhen Yihang Precision Circuit Co., Ltd. was founded on February 25, 2010. Since its establishment, it has been focusing on the research and development, design, production and sales of FPC flexible circuit boards as one of the high precision and high quality comprehensive company.
Products are widely used in mobile communication, smart home, optoelectronics, industrial control, medical equipment, automotive and consumer electronics and other fields.
This is a major area causing reliability failures.
• Root Cause: Copying the copper pouring and routing practices of rigid PCBs.
• Detailed Solutions:
1. Copper Pour Method: Solid copper pours are absolutely prohibited in flexible areas. Mesh copper pours (typically a 45° diamond mesh, line width/gap e.g., 0.15mm/0.2mm) must be used. Mesh copper effectively releases bending stress and prevents copper foil wrinkling and tearing.
2. Routing in Bending Areas:
• The routing direction should be perpendicular to the bending axis to distribute stress.
• No vias, pads, trace corners, or sharp angles are allowed in the bending area.
• All traces entering the bending area must have a smooth, gradual transition, avoiding abrupt width changes.
3. Shielding and Impedance: When shielding is required, flexible shielding layers such as conductive silver paste or copper mesh should be used preferentially. For impedance control lines, it is essential to communicate with the manufacturer early on so that they can provide accurate line width, spacing, and dielectric thickness parameters based on the specific stack-up and material characteristics.
* Root Cause: The connection between the pads and the flexible circuitry is a point of mechanical stress concentration.
* Detailed Solutions:
1. Pad Reinforcement: All connector pads and gold finger (test point) pads must use a "teardrop" or "patch" transition, and solder mask openings should be added to expose part of the copper foil, forming anchor points with solder.
2. Gold Finger Design:
* The fingertip shape should be a rounded rectangle, avoiding right angles.
* Use a "stepped" or "staggered" layout to distribute insertion and extraction stress.
* If space permits, a polyimide reinforcing plate can be locally adhered to the back (non-contact surface) of the gold finger.
3. Via Protection: Avoid directly drilling holes in the pads whenever possible. If unavoidable, ensure that vias are completely covered or filled, and perform plugging treatment to prevent solder loss and stress cracking.
