LASER ETCHING OF POLYMER MASKED LEADFRAMES

A typical electroplating production line for the deposition of silver pattern on copper leadframes in the semiconductor industry involves tw enty to twenty five steps of cleaning, pickling, plating, stripping et c. This complex production process occupies large floor space and has also a number of problems such as difficulty in the production of rubb er masks and alignment, generation of toxic fumes, high cost of water consumption and sometimes uncertainty on the cleanliness of the surfac es to be plated. A novel laser patterning process is proposed in this paper which can replace many steps in the existing electroplating Line . The proposed process involves the application of high speed laser et ching techniques on leadframes which were protected with polymer coati ng. The desired pattern for silver electroplating is produced by laser ablation of the polymer coating. Excimer laser was found to be most e ffective for this process as it can expose a pattern of clean copper s ubstrate which can be silver plated successfully. Previous working of Nd:YAG laser ablation showed that 1.06 mu m radiation was not suitable for this etching process because a thin organic and transparent film remained on the laser etched region. The effect of excimer pulse frequ ency and energy density upon the removal rate of the polymer coating w as studied.