TEST + QUALITY ASSURANCE Fatigue fracture pattern on the chip side of a bond wire lifter (lift-off). The BAMFIT test head is simply exchanged for another bond or test head on the machine base, so that standard pull or shear tests can be carried out interchangeably. If the machine already has an ultrasonic generator, this is also used for the tests. The machine software is identical to that used for bonding or testing. The training effort for the new test procedure is therefore comfortably low. A test run is straightforward: First, both the position and direction of the wedge bond contact are precisely located, and the clamp is then opened so that the clamp tips move past the wire as they are being lowered. Touching the bond surface is detected by the touchdown sensor; the clamping tweezers are then raised to the programmed clamping height and closed. In this state, at a defined distance from the bond surface, the bond wire is mechanically connected to the 60 kHz transducer from both sides with a constant clamping force via the clamping jaws. These clamping jaws are slightly longer than the wedge bond foot so that they project beyond it and achieve the largest possible clamping surface. During the entire duration of the ultrasonic signal, the bond force device applies a small constant tensile preload in the Z direction to prevent the connection from frictional re-bonding. This upward pull is so small that no additional damage is caused. The height sensor now allows to determine the exact time of failure when the wire lifts off. Efficient process optimization The ultrasonic power at the transducer can be adjusted and is directly proportional to the oscillation at the tip of the clamp jaws. These cyclic deflections are well below 1 μm and are therefore much lower than for the actual bonding itself. Depending on the amplitude applied, the number of cycles until complete lift-off is in the Source: F&S Bondtec range of about 10 4 to 10 8 and above. At an excitation frequency of 60 kHz, 10,000 cycles correspond to a measurement time of approx. 160 ms, which can still be clearly resolved at a measurement interval of approx. 15 ms. In a typical service life range of 10 to 100 times more cycles, a very acceptable measurement time of approx. 1.5 to 15 s is achieved. Thus, a rough lifetime prognosis is achieved simply by measuring the time from switching on the ultrasonic oscillation until the wire detachment. In this way, an entire layout can be programmed and tested automatically in a very short time. Start (source), middle (stitch) or end (destination) bonds can be gripped and tested in the same way, as long as they are accessible from above, similar to the bonding itself. For the precise positioning of already existing bonds, the program and the image recognition unit (PRU) of the Bond tester can be used advantageously for previously bonded wires. As a result, the number of load cycles until final lift-off is determined as a function of freely programmable oscillation amplitudes, which can be converted into shear stress values at the joint. There is a correlation between pure mechanical stress amplitudes and the reference junction temperature differences (∆ Tj) for PC tests. Finite element analyses can be used to convert between the thermally and mechanically induced stresses in the contact interface with great accuracy. The mechanically determined lifetime curves show remarkable good agreement with results from PC tests in the ∆ Tj range 50 to 160 K for the same failure pattern, a bond wire lift-off. The mentioned tester is already in series production with first manufacturers of power modules. It is expected to make a valuable contribution to efficient quality assurance and simpler process optimization for thick wire bonds. Further developments for the extension of the technology to copper heavy wire bonds as well as ball bonds with copper wire are already underway and are also showing very positive results. www.fsbondtec.at Zusammenfassung Bond-Drahtverbindungen müssen über mehrere Dekaden und unter hohen thermomechanischen Belastungen zuverlässig halten. Dafür sorgt ein Bondtester mit einem extrem schnellen automatischen Qualitätstest zur Lebensdauerbestimmung der Bond-Drahtverbindungen. Résumé Les connexions des fils de liaison doivent être fiables pendant plusieurs années et résister à des charges thermomécaniques fortes. Ceci est réalisé par un testeur de liaison dans lequel est incorporé un test de qualité automatique et rapide ; ceci afin de déterminer la durée de vie des connexions des fils de liaison. Резюме Контактные соединения с использованием гибких металлических проводников должны служить десятилетия в условиях серьезных термомеханических нагрузок. Качественное соединение можно обеспечить только при использовании высокоскоростного тестера, позволяющего в автоматическом режиме осуществлять контроль сварок. 86 EPP EUROPE April 2019
PRODUCT UPDATES TEST + QUALITY ASSURANCE 3D AOI and X-ray for high-volume production Viscom Inc. will exhibit their inspection systems at the SMTconnect tradeshow in Nuremberg, Germany. The company‘s portfolio include the S3088 ultra chrome, X7056-II 3D X-ray, and automatic inspection assignment. The S3088 ultra chrome is based on the company’s 3D AOI technology, and combines accurate defect detection with high inspection speed. This makes the system the first choice for efficient SMT production. Some of its features include inspection speed of up to 65 cm 2 /s and 65 mega pixels of information in each 50 mm x 50 mm field of view. The resolution is switchable, and with 10 μm per pixel even 03015 components can be reliably inspected. Together with the eight angled-view cameras, a virtually shadow-free 3D inspection is one of the key advantages of the system. Along with the high-performance hardware, the company delivers excit- ing new software features that enable automatic 3D program generation utilizing an extensive IPC compliant library, Gerber and centroid data to create a precise and comprehensive 3D image. With the unique 360View capability, side views of electronic components can be rendered in True to Life images. Automatic 3D X-ray inspection The X7056-II automatic 3D X-ray inspection system features high throughput and superb image quality for the requirements in highend electronics production. This new AXI in-line system can ensure precise inspection of hidden solder joints and components in production, including μBGA HIP (head in pillow) defects on bumps down to 0.2 mm Ø. The system is equipped with the xFastFlow transport module, which cuts printed circuit board transfer times. With this feature, up to three boards can be processed at the same time. The company‘s portfolio also includes their 3D SPI and Offline uCT X-ray systems. SMTconnect, Booth 4A-120 www.viscom.com Source: Viscom Inc. An advantage for the S3088 ultra chrome is its virtually shadow-free 3D inspection. Rapid test method to detect defects in protective coating The integrity of coatings of electronic assemblies to protect against interference, harsh climate conditions, and harmful gasses has a significant effect on the reliability of those assemblies. An inability to protect against such risks may lead to damages that result in an edge escape at connection contacts and pore channels in paint pooling areas, among other potential problems. By using the Coating Layer Test from Zestron, defects in protective coatings or non-closed layers in μ-coatings become visible via the appearance of black dyed indicators. This non-destructive test on closed and dense coating represents a significant upgrade from commonly used methods for coating thickness measurement. Therefore, the test can also be used during production for cost-effective sampling. www.zestron.com Zestron introduces rapid test method to detect defects in protective coating of electronic assemblies. Source: Zestron Europe Purity is Found in the Cold FR4 Laser Cutting without Carbonization The LPKF PicoLine 3000 and the new LPKF CleanCut Technology are defining all new standards for cutting printed circuit boards with a laser. www.lpkf.com/picoline-3000 SMTconnect: 7 – 9 May, Hall 5, Booth 434B EPP EUROPE April 2019 87
