Ball Bonder Research Articles

Aluminum Wedge-Wedge Bonding Using Capillary and Ball Bonder

Abstract The paper discusses on the bondability and reliability of aluminum (Al) wedge-to-wedge bonding using fine ceramic capillary and ball bonder. Initial trials revealed aluminum build-up and poor capillary life with touch down of 20K or less. Optimizing the process parameters, switching on air-scrub, reducing shape angle to 20° instead of usual 35° and using Al-1wt%Si wire processed with refined grains revealed better capillary life with touch down of 200K without surface burrs. The method is capable of bonding complex looping and sharp acute bends. The data comprising of 1st and 2nd wedge dimensions, wedge pull, wedge shear and fracture mode for 20μm and 50μm Al-1wt%Si wires are presented. High temperature storage of aluminum wedge bonding to different substrate surfaces such as Al-0.5wt%Cu metallization, bare copper and gold plating revealed stable bond. From the wedge pull and tensile data, floor and shelf life of the wire is recommended to be 7days and 6months respectively. Evaluation of gold, copper and silver base bonding wires by this method showed feasible to bond and needs detailed studies to practice. The fusing current of Al-1wt%Si wire for varying diameter from 0.6 to 3mil and wire length from 1 to 20mm are also stated.

Advances in Wire Bonding Technology for Overhang Applications

Abstract Wire bonding is the most popular interconnect technology and the workhorse of the semiconductor packaging industry. Wire bonding is widely used for 3D packaging in which multiple dies are often stacked vertically in a ‘stacked die’ configuration. In such packages, one or more dies may be unsupported in an ‘overhang’ (e.g. cantilever beam) configuration. Wire bonding on an overhang die causes die deflection. If not optimized, it may lead to improper ball shape, inconsistent looping, pad crack and die crack issues. Therefore, careful process optimization is needed to have the best outcome in wire bonding performance. This optimization is often tedious and time-consuming. Moreover, recent trends towards minimizing package size (e.g. ultra-thin dies) and increasing number of die stacks add to the challenges of optimizing a wire bonding process for overhang devices. This paper examines the challenges of wire bonding on overhang devices. Finite element analysis (FEA) of overhang devices is presented. Die deflection data obtained from the FEA correlates well with the experimental results obtained on the ball bonder. The FEA results show that die deflection increases significantly with decreasing die thickness and increasing overhang distance. Other factors such as substrate thickness, and bonding temperature also effect die deflection, although less significantly than die thickness and overhang distance. Various considerations for optimizing a ball bonding process on overhang devices are discussed. Experimental results of ball bonding optimization on 50 μm and 75 μm thick overhang devices with different overhang configurations are presented.

Study of 6 mil Cu Wire Replacing 10–15 mil Al Wire for Maximizing Wire-Bonding Process on Power ICs

Copper (Cu) wire-bonding with its advantage in cost, mechanical enhanced characteristic, and better electrical performance is a developing alternative interconnection technology to replace gold (Au) and aluminum (Al) wires in IC packaging manufacturing. This paper discussed the experimental study of using 6-mil Cu wire on an ASM wire bonder to replace 10-15 mil Al wire in a power IC device. It encompassed wire and tool selection, wire-bonding process development, post wire-bonding integrity inspection, and bonding reliability results. The wire and tool selection included type of wire, capillary use, and bonder capability. The process development focused on two crucial stages, Free air ball (FAB) formation and bonding process window development. Design of experiment (DOE) was extensively applied in this study. The experimental studies showed that flow rate of forming gas was a key factor to form the qualified FABs and establishment of a workable process window. Wire pull and ball shear tests were conducted per JEDEC criteria for bond strength integrity. Moreover, crater test and Zygo's 3-D measurement were used to inspect any risk of underlying metal integrity in die before reliability tests. The data showed that sufficient thickness of the Al bond pad was crucial to avoid any underlying metal damage when subjected to heavy copper wire bonding forces. High-temperature baking (HTB) and pre-condition (PC) and temperature cycle (TC) were used to evaluate the samples reliability. The results of the two reliability tests showed that Cu/AL intermetallic compound (IMC) growth was slow, which indicates potential significant product life-span extension. The study concluded that with current thermosonic ball bonder, using 6-mil Cu wire could replace heavy 10-15 mil Al wire in power IC applications.

The Effect of Ultrasonic Frequency on Gold Wire Bondability and Reliability

This paper presents a systematic study on the effect of 120 KHz ultrasonic frequency on the bondability and reliability of fine pitch gold wire bonding to pads over an organic substrate with gold metallizations. The study was carried out on a thermosonic ball bonder that is allowed to easily switch between ultrasonic frequencies of 60 KHz and 120 KHz by changing the ultrasonic transducer and the ultrasonic generator. Bonding parameters were optimized through the design of experimental methodology for four different cases: 25.4 μm wire at 60 kHz, 25.4 μm wire at 120 kHz, 17.8 μm wire at 60 kHz, and 17.8 μm wire at 120 kHz. The integrity of wire bonds was evaluated by six response variables. The optimized bonding process was selected according to the multiattribute utility theory. With the optimized bonding parameters developed on one metallization for each of the four cases, 8,100 bonds were made on five different metallizations. The samples were then divided into three groups. The first group was subjected to humidity at 85°C/85% RH for up to 1,000 h. The second group was subjected to thermal aging at 125°C for up to 1,000 h. The third group was subjected to temperature cycling from −55°C to +125°C with 1 h per cycle for up to 1,000 cycles. The bond integrity was evaluated through the wire pull and the ball shear tests immediately after bonding, and after each 150, 300, 500, and 1,000 h time interval in the reliability tests. Results show that 120 kHz frequency requires less ultrasonic power than 60 kHz when all other parameters are equal. The results also indicate that bonding at 120 kHz frequency is less sensitive to different metallizations than bonding at 60 kHz. All three reliability tests do not negatively affect the bond integrity of Au wire bonds on a variety of Au metallizations for both frequencies. Furthermore, as the reliability test time increases, both pull and shear strengths of Au wire bonds on Au pads increase.

A Study of the Copper Wire Ball Bonding Processes

ABSTRACTCopper ball bonding is a new technology which is expected to replace the traditional gold ball bonding and paid attention in woled recently, the technology is very important to reduce cost and improve reliability of microelectronic components. In this paper, the copper wire ball bonding processes have been studied by means of the MW-EFO metal wire ball forming device and the JWYH-2 thermosonic ball bonder. The bond strength of the ball bond under varied ultrasonic power and bonding time have been tested. The tested results show that the maximal strength of copper ball bond can be over 20g, it has advantage over the gold wire ball bonding. In this paper, the deformation process of the copper ball bond has been analyzed and viewed by SME.