chemical etching
Chemical etching is one of the most popular and widely used methods for manufacturing lead frames. While mold machining may be considered a high unit cost process, it is very cost effective and very time efficient.
Etched leadframes are manufactured from a flat sheet, typically made of copper or an iron-nickel alloy (such as Alloy 42), which has a very low expansion rate at room temperature.
These low thermal expansion alloys have found use in modern applications where metals need to be joined to glass or ceramics, and in areas where the materials to be joined need to have the same rate of thermal expansion to prevent related problems within the joining area.
Both sides of the flat alloy sheet are cleaned and then photoresist is laminated. The photoresist is then exposed to the desired lead frame pattern with the help of a UV source and a precision patterned film. A resist is formed over the areas to be etched away, and the remaining resist protects the part during the etching process.
Finally, the protective photoresist is peeled off the finished leadframe before the etched panel is singulated into strips, or is provided in sheet form upon customer request for easier handling. The cut strips are cleaned and plated, often with silver on the inner leads to facilitate wire bonding. The plated strip is then ready for final inspection.
stamping
Stamping is an automated, high-speed process suitable for high productivity and can withstand high initial tooling costs. Sheet metal (usually in roll form) is perforated along both edges to create index holes that position the sheet metal during further processing. Pilot holes are used to advance the metal lath through the punch. A die set specific to the lead frame geometry is also required.
The process is typically accomplished through a series of stamping operations that progressively approach the final leadframe geometry, with the number of steps entirely dependent on the complexity of the leadframe geometry.
