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Posted on 06 July 2019

Heavy Wire Bonder Platform with 30% Increased Productivity

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The wire bonder sets a benchmark

An increase in produced parts per hour at reduced production costs and same or better quality is a continuous demand for the development of new manufacturing equipment. These demands have given the direction for the development of the new series Bondjet BJ93x, which will set the benchmark for heavy wire bonding, also from a throughput point of view.

By Herbert Stürmann, Hesse & Knipps Paderborn

 

A significant proportion of the cycle time for wedge bonding, especially in the largest wire diameter applications, is used for the ultrasonic welding process. For this reason it is a big challenge to achieve a 30% increase in productivity. Each element of the bonder series BJ92x had to be questioned for means of optimization. Consistent reduction of the moving mass, integration of highly dynamic linear motors and the proven axis control system of the BJ82x bonder series have lead to double acceleration values of all axes. The bondhead with 20% reduced mass was equipped with a new set of actuators, optimized for low moment of inertia. Big emphasis was also put on the selection of components which are maintenance free or mostly wear free in their application.

The new machine generation is based on long term experience in the development and design of ultrasonic wedge-wedge bonders, the consistent application of mechatronic design principles and the integration of micro technology for sensors and actuators in the new bondhead generation. The new machine generation uses our ultrasonic generators based on DDS technology – already field proven from the fine wire bonders - and optimally matching amplifiers and transducers.

At the Productronica 2009 the Bondjets BJ935 and BJ939 had been presented, setting a benchmark for the processing speed as well as precision and low maintenance requirements. This claims worldwide technological leadership under the heavy wire bonders, as with the fully automatic Wedge- Wedge Thin Wire Bonders series BJ820.

Machine Generation Bondjet BJ935 and BJ939

The Bondjets BJ935 and BJ939 deliver the basis for a new machine generation with proven technology and innovative development for the processing of aluminum wire, copper and ribbons.

Heavy Wire bonder Bj 935

The application of proven technology and innovative solutions means:
• Gantry kinematics with linear motors for current and future requirements on precision and repeatability with working areas up to 350mm x 500mm
• Reduced mass bondhead with integrated, non-destructive pull test.
• Active cutter system, decoupled from the Z axis
• E-box, optical setting assistance for cutter, wire guide and wedge tool (patented)
• PiQC, process integrated quality control for stress-free monitoring of each bond (patented, patent application).

With features such as active cutter, E-box and PiQC, Hesse & Knipps already set essential trends and henceforth sets the benchmark for the cost of ownership. The power of innovation lies with the combination of dynamic drives, optimized axis control concepts, high speed compliant kinematics for all axes and innovative bondheads, optimized for high functionality and low mass. Productivity increase of 30% compared to the current machine generation BJ920 have been reached during evaluations with IGBT modules, confirming that the set target was reached in full.

Concerning the achievable bond quality, the new machine generation is also setting new benchmarks: The touchdown of the wedge tool on the chip or substrate can be executed with highest sensitivity. Placement accuracy is increased 3 to 4 times compared to the series BJ92x bonders. The repeatability of looping is ± ½ wire diameter as a general thumb rule. With these properties the new machine generation is well prepared for ever smaller bond pads and ever thinner and therefore more sensitive contact layers on the semiconductors.

Established features such as frontcut-backcut retrofit within minutes, fast bondhead exchange including wedge calibration, easy integration in production lines, universal or customer specific automation were taken over as well as the user friendly software.

The new machine series can be integrated into existing production lines and existing automation can be easily adapted.

The extra large working area of up to 350mm x 500mm allows smart automation concepts or processing of extra large substrates.

Quality control – the state of the art

For the prediction of bond quality it is common to measure the transducer current or the electrical progression of admittance or impedance respectively and the progression of wire deformation. The recent introduction of digital ultrasonic generators has allowed the resonance frequency to be added to the measurement. This frequency is subject to small variations during the bond process. To judge the bond quality, all of the measured signals are compared to the expected target progressions for deformation, current and frequency after the bond was formed. The above mentioned measurements allow detection of several likely bond defects, a complete detection of all possible defects however is not possible because the expected signal progressions are only necessary, but not sufficiently determining properties of the bond quality. To explain this in an example: A progression of wire deformation outside the expected target progression will immediately give evidence to a poor quality bond. On the other hand bonds on a contaminated surface will often exhibit a deformation progression within the target range, even so the bond is of insufficient quality. The expected target progression of the wire deformation is therefore not a sufficiently determining quality criteria. This simple example furthermore shows that a closedloop control forcing the wire deformation into an expected progression by altering the force and / or ultrasonic output during bonding will not solve the fundamental problem of the above example and is therefore useless. The existing methods for quality control allow the operator to monitor the bond process within defined process parameters through a defined process window.

The ultrasonic output follows a predefined profile during bonding. This guarantees that there is always the same amount of energy available to carry out the welding. For this reason there is no triggering of ultrasonic change by deformation with Hesse & Knipps bonders.

Bondhead with integrated non-nondestructive

PiQC, the world wide unique process integrated quality control

With PiQC, Hesse & Knipps introduced a quality control system which uses additional sensors to open up a wider range of process parameters to be added to the quality evaluation. Such parameters are the mechanical impedance, the velocity of the wedge tip and the friction value between the wire and the bond surface, which is the point where the energy for welding is applied. For heavy wire bonders, non-destructive tests are required in fully automatic production which enable 100% control and ideally detect all quality errors. Despite the high bond speed, all Hesse & Knipps bonders can compute a vast amount of process data in real-time parallel to the welding process without compromising the machine productivity.

E-Box patented (US-07461768 B2 and DE103 38 809-B4)

As is the case with the above mentioned available methods, the additional signals from the bond process (when viewed isolated) are also not able to deliver a determining quality criteria for a welding process. The collective sum of all parameters which are now available for analysis does provide such a criteria. In other words: there has not yet been any bond defect observed, which did not trigger at least one of the parameters to respond with an outlier. PiQC therefore provides a reliable bond quality criteria for the first time world wide. Large scale parallel computing – main algorithms are implemented in VHDL – provides the result in realtime, allowing PiQC to be applied as a 100% quality control. The necessity of statistical process control by destructive testing can be reduced significantly and – in an optimized production process – be even basically eliminated.

PiQC provides a quality control system which does not apply any mechanical stress to the bonds. This is a significant advantage over partially applied mechanical nondestructive inline test systems, which clamp the wire after bonding and apply a predefined force to the bond. Bond defects such as non-sticks can be detected by such methods, however the mechanical stress and the time of such tests are significant disadvantages. PiQC does not limit the machine productivity because the test is carried out parallel to the bond process. PiQC can therefore be activated for every bond and is – as already mentioned – free from feedback to the welding process. A more extensive quality system than the patented PiQC is world wide unknown.

Cost of ownership and quality are decisive attributes for production machines in the power electronics. The new machine generation BJ935 and BJ939 satisfy this demand in every aspect. 

 

 

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