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VOLUME -22 NUMBER 7
Publication Date: 07/1/2007
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July 2007 Issue
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Heavy Wire Bonding: New Standards, New Machines
BONDJET BJ920 Heavy Wire Bonder.
By Herbert Sturmann, Dipl.-Ing., Hesse & Knipps, Paderborn, Germany
Heavy wire bonding is always at risk from residual vibrations. The industry has long been aware of this problem and has been waiting for much needed improvements in heavy wire bonding technology. Movement of the bonder axes can cause the entire assembly to vibrate (residual vibrations). If this does not subside during the bonding process, the fabricator ends up with serious quality problems — from the lack of reproducibility and the difficulty of making accurate measurements during the bonding process.
Without improvements in heavy wire bonding technology, the risk of damaging components with increasingly sensitive semiconductors is considerable. Tools are also long overdue that prevent setup variations from shift-to-shift and operator-to-operator. Another challenge has been to develop non-destructive tests for heavy wire bonders that examine a wide range of potential quality errors — tests that provide for 100 percent control of the process. There is help on the scene; the newest heavy wire bonding equipment designs implement multiple features to combat these production issues and significantly improve bond quality for fully automatic heavy wire bonding.
This new generation of heavy wire bonders is equipped with state-of-the-art sensor and control technology. It is this technology which ensures that machine vibrations have no disturbing influence on the welding process, or that the vibrations do not occur in the first place. Furthermore, the sensors do not require calibration. These new heavy wire bonders integrate optimum touchdown detection of 300ms with virtually no signal propagation delay and high precision 0.1µm resolution bondforce control to ensure the highest level of quality. With this newer control system technology, bondforce is controlled to ±1 cN accuracy, and the risk of damaged components and field failures is significantly reduced.
Active Cutter System
A new, longer lifetime active cutter system for heavy wire bonders has been developed that is decoupled from the Z-axis and requires no pusher. This immediately increases the free space for bonding inside packages.
The system enlarges the setting window for cutting, allowing a much quicker cut process. Highly repeatable cutting system accuracy improves quality considerably while preventing the risk of cutting into the substrate. The system produces consistent cut depths, even allowing for tolerance variations in the product.
Maximum accuracy is required when changing out the wedge, cutter, and wire guide; incorrect tool settings can spell disaster for product quality. The solution to this problem is now available; new tools include the E-box
developed by Hesse & Knipps for the BONDJET BJ920 Heavy Wire Bonder allows micron-precise tool settings and immediate visual control by the operator, thereby preventing shift-to-shift and technician-to-technician setup variations. Control procedures and readjustments become unnecessary while the lifetimes of the wedge, cutter and wire guide are increased. The E-box reduces the time required for tool setup compared to the typical procedure by about 70 percent.
Bondhead Quality Tests
Pull tests can verify the integrity of each individual bond compared to limits set by the user, based on the application. The pull test provides a quantified value for the strength of the interconnected wire to the die or package up to the tensile strength of the wire itself on a superbly bonded wire, or the weakness of the over-squashed wire at the heel or toe of the bond.
In addition, pull tests can identify cratering, a defect that can occur when the entire bond and a piece of the die pad lift off the die during the pull test, leaving a crater in the die pad. Shear tests measure the strength of the intermetallic connection, revealing weak points in addition to any cratering beneath the bond pad.
Heavy wire bonder wedge, cutter and wire guide setup feature.
Only the newest heavy wire bonding equipment integrates both types of non-destructive tests to examine a wide range of possible quality errors and allow 100 percent control for heavy wire bonding applications. Hesse & Knipps has developed and applied for a worldwide patent on the only bond head available in the industry to incorporate both integrated pull test and integrated shear test. Sensors integrated in the bondhead enable fast and safe pull and shear tests set by the user based on qualitative targets.
Both pull and shear test functions are integrated into the bondhead such that the free space around the bondhead is unrestricted — the heavy wire bonder can be used in all applications without restrictions.
Process Integrated QC
Taking the next step, a new wire bonding process control system is under development and is being field tested; this "Process Integrated Quality Control" (PIQC) system enables the acquisition and assessment of several feedback values which influence bond quality. The PIQC provides a graphic representation of the output of present bonding conditions set against an acceptable range, and notifies the user of conditions outside of this range so that settings can be adjusted as required.
Heavy wire bonder users are gaining confidence in the PIQC system and expect that it will remove some of the risks associated with bonding, greatly reduce yield losses for inconsistent bonding. And there is hope that it may even replace some of the third operation inspection requirements typically required for heavy wire bonding applications.
On the horizon is state-of-the-art heavy wire bonding equipment that will include a large working area up to 380 x 500mm, intelligent and complete software, specifically developed pattern recognition, transducers with different frequencies, fully digital generator with a wide frequency range. Users of heavy wire bonding equipment should be able to demand a machine concept that fulfills their most demanding requirements from automotive to lead frame and ribbon bonding applications.
For more information, contact: Hesse & Knipps, Inc., 2305 Paragon Drive, San Jose, CA 95131
408-436-9300 fax: 408-436-2822 E-mail: email@example.com Web:
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