Fine Gold and Coated-Ag Bonding Wire: Vertical Wire Bonding

Wire bonding is an important technique in microelectronics packaging; high precision vertical wire bonding (vertical array arrangements) is investigated in detail in the memory sector with stacked devices. This study focuses on the development of vertical wire bonding using bonding wires ranging from 18 to 30μm in diameter, including gold (Au), silver (Ag), and copper (Cu) based wires. The vertical wire bonding method is evaluated on four stacked and conventional devices. Factors such as vertical wire post height, wire diameter, and wire elongation are examined. Bonding assessments encompass a range of vertical wire post heights from 100μm to 1mm. A stable bonding process window is determined for a low variation in post height (ΔH) within 10μm for tested ranges from 150 to 500μm. Wires with moderate ductility, exemplified by a 4% Elongation (EL) in 4N (99.99%) Au and Coated-Ag, exhibited with low variation in X-shift and Y-shift, along with post height across the studied elongation range of 2-8% EL. All the examined wire types: 4N Au, 2N (99%) Au, gold coated silver (Coated-Ag), Alloyed-Ag, gold flash palladium (Pd) coated copper (AFPC), and bare Cu (soft 4N Cu), met the precision requirements for vertical wire bonding. The study reveals that vertical wire bonding, a key process for microelectronics assembly in stacked devices, can be achieved with a collection of wire materials, given that proper attention is directed towards optimizing factors such as wire diameter, elongation, vertical wire post height, and capillary types/dimensions.