Issue link: https://iconnect007.uberflip.com/i/1515637
FEBRUARY 2024 I DESIGN007 MAGAZINE 69 A poor design is shown in Figure 4. Note that the line and space ratio is not designed to be even. ermal distribution from the bonding head must be homogeneous for ACF adhesive to cure properly. An example with a large line width is shown in Figure 5. Large gold areas are not necessary; adhesives actually have lower adhesion on a gold surface. Large leads can be divided among multiple leads. In Figure 6, we see a comparison of an appro- priate design and a poor design. Leads should be designed in a straight and simple line to provide enough thermal compression from the bonding head. When the ACF bonding area is to be applied on the center of two bonding lines with the design shown in Figure 7, seepage of the ACF adhesive will not be good enough to pass the peel strength test. e rear lead running on the back side of the flex circuit should not be located on the center of a lead on the front side. Figure 8 shows two similar but less than opti- mum designs. e back side lead should not be designed between leads on the front side (le). Avoid any circuit design that may cause a short by allowing conductive particles to become jammed in between leads (right). Figure 4: A poor design. Different thermal conductive lead widths will complicate temperature verification. Figure 7: Example of the ACF bonding area on the center of two bonding lines, which can affect peel strength. Figure 6: A good design (left) and a poor design (right). The poor design may cause partial compression, because only the crossing point could be compressed on the back side of the flex circuit. Figure 5: With large line widths, large gold areas are not necessary.