Opportunities on prolong battery stand-by time

A foresight study has been successful conducted on minimizing leadless package leakage current to prolong the battery standby time. Nowadays, smart phone industry is booming in global marketplace and the latest metrics data shows a continuous rising. It can foresee that the market is looking for a longer and longer battery life. Package leakage current plays important roles for this need, especially for the minimization package with smaller lead pitch. A novel leadless package leakage current mechanism is built and concluded by an extensive analysis and process mapping etc.. It is found that the backside thermoplastic leadframe tape composes of poly-amide-imide layer could be activated by die bonding & wire bonding process with a high temperature and a long duration. During the molding process, the activated tape reacts with the catalysis in biphenyl epoxy based molding compound (EMC) and result a slightly conductive surface with amide group on the EMC. It is well known that amide can be hydrolyzed in acid or base with the formation of carboxylic acid or carboxylate anions. With the considerations of the facts that the chemicals used for deflash is mainly composed of sodium hydroxide with a high pH value and the chemical used for plating contains Solderon acid which is very acidic, it was believed that the polymer chains containing amide group on the molding compound surface was hydrolyzed in proceed processes. After hydrolysis, the carboxylic acid would attract the Sn ions in the plating bath. The existence of these ions on the molding compound surface would cause the current leakage. Based on this novel leakage mechanism, three independent remarkable industrial solutions are suggested and proven. 1) Use non-PAI adhesive layer leadframe tape. 2) Use EMC without the catalysis which can activate tape & EMC. 3) Skip the plating process.