The transition from fine-pitch (FP) to ultra fine pitch (UFP) volume production, and the emergence of stacked-die, CSP and ultra low loop bonding has increased the level of difficulties in wire bonding process. In compliance with these new bonding requirements, a new generation and high performance design, known as the PI (Programmed Intelligence) capillary has been developed.
Superior bonding performance with good repeatability and portability for a broad range of complex bonding applications.
Applicable for FP & UFP bonding, ULL bonding, CSP bonding, low-k bonding & stacked-die bonding.
More responsive to the bonding parameters, producing better bond integrity.
Low-K Wire Bonding Capillaries
The process for low-k device bonding is very sensitive especially for ultra-fine-pitch bonding. In fact, the most challenging problem with low-k wire bonding is ball bond reliability. A polymer-induced bonding problem occurs when the bond pad is small. If the polymer is soft or heated above its Tg during thermosonic bonding, the small bond pad can partially sink into the polymer during application of bonding force. This lowers the effective bond force after the capillary contacts the pad, and therefore higher ultrasonic energy is required. ‘Cupping’ or sinking can damage low-k diffusion barriers and results in failure.
Problems associated with low-k wire bonding are as follows (typical failure reject criteria):
Non-sticking on bond pad
Metal peeling / de-lamination
Damaged / fractured bond pad
Effects of probe marks
Poor bond shear strength
Although wire bonding has been a well-established technology for many years, the bonding tool design becomes more complex and the process is very sensitive for wire bonding of low-k devices. Stability of ultrasonic energy transmission and lower ultrasonic-generator power are needed to prevent pad damage. From the various evaluations and analysis conducted, the PI capillary design showed the best attributes in terms of efficiency of ultrasonic energy transfer and better bond integrity. Together with the DFX feature, the PI-DFX combination has shown to reduce pad peeling and improved bond integrity with higher percentage of inter-metallic compound in the bond interface.
Stacked-Die Wire Bonding
The demands for high electrical performance and pin count have resulted in significant advances in integrated circuit fabrication and microelectronics packaging. As the popularity of mobile phones, digital cameras, personal digital assistant, etc drives the move towards smaller geometry chips, new packaging method needs to be developed to integrate highly complex chips into the smallest possible space.
The miniaturization of such products was made possible by the application of stacked-die Chip Scale Package (CSP) packaging technology. Indeed, the demand for small form factor packages, increased functionality in the same area, and low cost are the product requirements for stacked-die CSP’s. Inside the stacked-die CSP’s, it contains 2 or more dice, stacked over each other. Wire bonding is most commonly used for interconnection.
Stacked die packaging is the most versatile wire bonded package among all other packages. It came in different design configurations - from pyramid stacking to overhang stacking, from standard bonding to low loop and reverse bonding. Given the complexity of the chip configurations, capillary design needs to be optimized for each particular bonding configuration.
Pyramid stacking is a conventional chip stacking. Dimensional selection as per standard capillary selection guide. However, as more and more chips were stacked, the wire length for the upper chip increases. Wire sway could be a major issue. PI Capillary design has been used extensively to minimize wire sway issue, especially for long loop application.
Overhang and same die size stacking. Die deflection due to the impact force during bonding, especially at the corners of the die can result in NSOP. Normally parameter optimization or re-grouping of the corner wires is necessary. Reverse bond using ball stitch on ball technique is normally used to achieve the low loop height requirement.
It should be noted that stacked die bonding represents one of the most complex bonding in the wire bond process. Within one package, different bonding techniques using forward bonding, reverse bonding, multi-tier bonding together with the new loop trajectory can be performed. Again, each type of bonding has its own uniqueness and need to be considered separately when selecting the optimum capillary design.
Multi-Tier wire bonding
Multi-Tier wire bonding offers an alternative to increase the number of I/O beyond 1000 wires without having to reduce the pad pitch, especially for those chips used in graphic cards and chipsets. Multi-tier bonding is not new in the industry. Staggered wire bonding for fine-pitch and ultra-fine pitch has been around for a long time. Currently, volume production for multi-tier wire bonding was limited to 60um bond pad pitch (BPP) for tri-tier wire bonding and 70µm BPP for quad-tier wire bonding.
The introduction of quad-tier wire bonding requires that capillary designs be reassessed. Increased capillary bottleneck height is required to prevent contact with adjacent wires. However, this change has the potential to degrade capillary reliability as well as bond quality, due to a reduction in the efficiency of ultrasonic energy transfer from the bonding tool to the bond interface. Through physical modelling of the capillary using customized software, the different capillary profiles were evaluated in the context of their interaction with the looping profile that would be encountered during actual bonding based on the quad-tier configuration.
Finite element analysis (FEA) was also used to analyse the effect of different bottleneck height values. This is a potential significant issue, because it could increase the risk of capillary breakage during production run. FEA was used specifically to study the stress level at the tip and the transition profile for different designs, as these are the locations where breakage is most likely to occur.
From the various evaluations and analysis conducted, the PI Capillary design showed the best attributes in terms of efficiency of ultrasonic energy transfer and better bond integrity.
Capillary Part Number Selection Guide
The capillary design selection guide is always based on specific device & package configuration, wire type, and wire bonder. The selection of capillary part number process is simplified as follows:
Capillary Tip The selection of capillary tip design is determined by the device and metallization, bond pad pitch, bond pad opening, wire size, target mashed ball diameter, and critical loop height to derive the hole diameter(HD), chamfer diameter (CD), chamfer angle (CA), tip diameter (T) and face angle (FA).
Shank Style The shank style selection is characterized by geometrical design of the capillary bonding tool as dictated by specific device and / or package configuration.
Surface Finish The selection of a particular capillary tip surface finish hinges on whether the application is for gold or copper wire bonding.
Material Capillary material selection for optimum tool life performance for a given bonding application.
Wire Type The proper selection of capillary design is a resultant of the various wire bonding considerations.
Fine Pitch Part Number Selection
Infinity 3X Longer Tool Life
SPT 'Infinity' capillary material extends the tool life up to 3X its original tool life. This option is available on many tools and is a proprietary process SPT use to increase tool life.
ORDERING INFORMATION (PLEASE ADVISE REQUIREMENTS & QUANTIY FOR QUOTE OR ASSITANCE)
Part Number - PI Series Low-K, Multi-Tier and Stacked-Die Wire Bonding CapillariesLow-K-Multi-Tier-Stacked-Die Wire P.I. Capillaries Brochure
BONDING CAPILLARIES & ACCESSORIES WE OFFER:
UT NON-FINE PITCH CAPILLARIES
QFN PACKAGE COPPER & GOLD WIRE BONDING CAPILLARY
COPPER WIRE BONDING CAPILLARY
ENHANCED STITCH BONDABILITY
ADVANCED BONDING APPLICATIONS
AZR LONG LIFE MATERIAL FOR CU WIRE BONDING
INFINITY 3X LONGER TOOL LIFE