When Less is More

摘要

This month's question: What is the typical industry standard for tolerance on the length and width of a flex circuit and also for stiffeners? Answer: When it comes to dimensioning and tolerancing flexible circuits, less is usually better. Too many designers try to dimension a flex circuit as if it were a machined piece of steel. Keep in mind that the materials used to fabricate a flexible circuit are flexible. In addition to standard manufacturing tolerances, factor in the flexibility and dimension instability of the materials used in the construction. A lot of factors cause flex circuit materials to grow or shrink before, during and after the circuit is constructed. Major physical factors that contribute to the dimensional instability of a flexible circuit are temperature and humidity. Like any material, polyimide film and acrylic/epoxy film adhesive (by far the most common building blocks for a flexible circuit) will expand when heated and shrink when cooled.