Bonding Capillaries Bonding Evolution 2018 by SPT - Small Precision Tools

More catalogs by SPT - Small Precision Tools | Bonding Capillaries Bonding Evolution 2018 | 41 pages | 2018-02-19


Page 11 of Bonding Capillaries Bonding Evolution 2018

gold ball wire bonding process thermosonic tailless ball and stitch bonding is the most widely used assembly technique in the semiconductor to interconnect the internal circuitry of the die to the external world this method is commonly called as wire bonding it uses force power time temperature and ultrasonic energy also known to as bonding parameters to form both the ball and stitch bonds typically for the ball bond the metallurgical interface is between gold au and aluminum al bond pad usually with 1 silicon si and 0.5 copper cu as for the stitch bond it is bonded to a copper alloy with thin silver ag or nickel-palladium nipd plating the ultrasonic transducer typically for new generation of wire bonders the piezoelectric element is >100khz which converts the electrical energy into mechanical energy transmits this resonant energy to the tip of the bonding capillary the capillary that is clamped perpendicularly to the axis of the transducer-tapered horn is usually driven in a y-axis direction vibration mode bonding capillaries are made of high-density alumina ceramic material al2o3 typically 1/16” 0625” 1.587mm in diameter and .437” 11.10mm in length the final capillary design depends upon the package device application and wire diameter to be used to determine the correct capillary design in general bond pad pitch bpp bond pad opening bpo and target mashed ball diameter mbd are essential a fine gold wire made of soft face-centered-cubic metal fcc usually ranging from 18µm to 33µm in diameter depending upon the device package application is fed down through the capillary it is usually characterized by its elongation shear strain and tensile strength breaking load selection of the appropriate wire type to be used for a given application would be dependent on the specification of these elongation and tensile strength in general the higher elongation or higher strain it means that the wire is more ductile this is a good choice for low-loop and short wire type of wire bonding application if the requirement is for higher pull strength readings a harder wire type having a higher tensile strength has to be considered the small incursions of ultrasonic energy at the tip of the capillary are transmitted to the au ball and down to the al bond pad to form the ball bond after which the capillary lifts up and form the looping profile and then comes down to form the stitch bond this cycle is repeated until the unit is bonded an intermetallic compound au-al is formed when the au is bonded thermosonically to the al bond pad metallization the metallurgical interface of void free au-al formation has a significant increase in the shear strength readings of the ball bonds tested provided that there are no impurities present in the bond interface even if it has been exposed to high temperatures however if the impurities in the interface are welded poorly the ball shear strength produces a significant degradation in its readings 2 1 3 6 5 4 the bonding cycle back to content 11