Two-Layer Rt-QFN: A New Coreless Substrate Based on Lead Frame Technology

Abstract

Lead frames have been widely used in the semiconductor package assembly industry; a lot of demand is still maintained in fields requiring high reliability, such as automobiles, although many fields are being replaced by laminated substrates according to the recent electronic package product trend that requires high I/O pin count. The purpose of this paper is to introduce two-layer Rt-QFN, one of the lead frame-based coreless substrates. (Rt-QFN is a trademark of Haesung DS, which means premold type lead frame substrate.) two-layer Rt-QFN can secure more advanced design freedom compared with the lead frame and thus has I/O pin count coverage intermediate between the lead frame and laminated substrate. In addition, Rt-QFN can exhibit excellent heat dissipation performance by replacing via holes of the laminated substrate with Cu bumps formed by etching. CAE analysis showed that the thermal resistance of the two-layer Rt-QFN substrate was about 23% lower than that of the laminate substrate. The excellent heat dissipation property of two-layer Rt-QFN allows it to replace the existing expensive ceramic substrate and can achieve cost savings. In addition, the sputtering technique, including the LIS (Linear Ion Source) module, was introduced as a method to sufficiently secure the interfacial adhesion between the resin/Cu interface, which is a key factor in producing a two-layer substrate. As a method to enhance the interfacial adhesion between the resin/Cu interface, the collimated mode of LIS was used in the Ar atmosphere inside the vacuum chamber to activate the resin surface. After plasma pretreatment on the surface of the resin, a Cu seed layer was continuously formed by sputtering. As a result, it was possible to secure the high reliability of the two-layer Rt-QFN substrate, and it was confirmed through the evaluation of interfacial adhesion of more than 1.2 kgƒ/cm during the peel-off tape test at the resin/Cu interface and further moisture absorption evaluation.