RSA/RSP
RSA/ RSP is a selective plating technology using dry film-based photoresist as masking material. Photoresist is laminated onto lead frame surface as protective layer from plating; while pre-defined pattern is written onto the photoresist using UV lithography such that selective areas of the photoresist can be removed during developing process, exposing those areas intended to have noble metal deposition on top. The noble metal can be a single layer of silver (i.e. RSA), or 3 layers of nickel/palladium/gold (i.e. RSP).
Compared to the conventional mechanical mask plating, RSA/ RSP offers excellent plating positional accuracy down to 15μm, eliminating unwanted thin film of noble metal plated (leaked) onto the lead frame side wall, and very high degree of freedom in plating area design, e.g. single-ring, multiple-ring, or even tiny dot array with Ø100μm for flip-chip package, etc.
Hybrid Plating
QFN packages are widely used in the electronics industry for their small size, low cost, and excellent thermal and electrical performance. However, popular QFN lead frame plating options including selective Ag plating, full coverage Ni/Pd/Au (PPF) plating, or even bare copper surface have certain limitations to comply with or satisfy all the requirements from package assembly to SMT process: die attach glue wetting-ability, wire bonding compatibility, flip-chip solder bump wetting control, solderability of exposed DAP and terminals, cost concern on precious metal usage, etc.
To overcome these challenges, AAMI is capable to offer a hybrid photomask plating scheme for QFN lead frames: Ag is selectively plated as bonding pads on top side of lead frame, while PPF is selectively plated on bottom side as surface finishing for SMT terminals. Top side Ag brings several advantages including good compatibility with popular bonding wire types (Au, Ag, PCC, etc.), prolonged bonding capillary usable life for lesser wear-out; bottom side PPF allows direct SMT without the need of additional wet solder plating after encapsulation. Furthermore, photomask plating gives high design flexibility especially important to flip-chip semiconductor, and improves package reliability performance due to more exposed copper.
Mechanical Mask Selective Ag Plating
Mechanical Ag plating is a plating process that uses a mechanical mask to cover non-plating area. Compared to photomask plating, it is more cost-effective because it eliminates the use for expensive photomask, and the mechanical mask can be reused over a certain period of time. However, the plating position accuracy of using mechanical mask is inferior to that of photomask due to alignment tolerance. Additionally, since mechanical plating is performed after etching or stamping, there is a certain silver-plating leakage (bleed-out) occurring at the side walls of the lead frame. The choice between photomask and mechanical mask plating depends on the quality and cost requirements of the semiconductor package. AAMI has extensive experience and can provide professional advice to customers in selecting the appropriate plating method for specific need.
Super Strong Anti-Tarnish (SSAT)
The idea of Multi Chip Module (MCM) is to put different semiconductor chips possibly made by different companies, technologies or materials into a single package for better cost-performance (cost, space reduction), flexibility, time-to-market, etc. Its application is not limited to advanced packaging, but also QFN featuring with multi-pads. The multiple die attach (thermal curing) processes would cause significant surface oxidization over copper-based lead frame. This uncontrolled copper oxide layer is one of the key contributor to package delamination, resulting in reliability failure. Conventional or popular anti-tarnish chemical is designed for one-time single die attach curing process, thus insufficient protection against multiple-process. In view of market trend, we have developed a super string anti-tarnish treatment to strongly elevate the lead frame anti-tarnish capability, and it can also be tailor-made to fit for different thermal loading requirements.
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