Thomas Zerna

X-ray computed tomography on miniaturized solder joints for nano packaging

The challenge of nano packaging requires new nondestructive evaluation (NDE) techniques to detect and characterize very small defects like transportation phenomenon, Kirkendall voids or micro cracks. Imaging technologies with resolutions in the sub-micron range are the desire. But what does nano packaging mean? High end semiconductor industries today deal with functional structures down to 45 nm and below. ITRS roadmap predicts an ongoing decrease of the ?DRAM half pitch? over the next decade. Nano packaging of course is not intended to realize pitches at the nanometer scale, but has to face the challenges of integrating such semiconductor devices with smallest pitch and high pin counts into systems. System integration (SiP, SoP, Hetero System Integration etc.) into the third dimension is the only way to reduce the gap between semiconductor level and packaging level interconnection. The task is not only to identify any impurities on the package surface, but also to look as deep as possible into the package volume. Available non-destructive evaluation (NDE) methods for such kind of packaging are for example X-ray microscopy, X-ray computed tomography, ultrasonic microscopy and thermal microscopy. An overview was presented in. To investigate and discuss the limitations of the current NDE techniques and to find new ways to solve these problems the German government (Federal Ministry of Education and Research - BMBF) supports the research project ?Destructive and non-destructive evaluation techniques to characterize nano-scaled defects in highly miniaturized solder joints -nanoPAL?. The Electronics Packaging Lab and the Center of Microtechnical Manufacturing are the responsible institutions for the non-destructive testing part in this public project and main parts of the content of our presentation are results of this work focused on X-ray nano focus microscopy and nano focus computed tomography. This paper discusses the potentials and the limits of X-ray NDE techniques, illustrated by crack observation in solder joints, evaluation of micro vias in PCBs and interposers and the investigation of soldering quality of BGAs. The paper presents tomography results with voxel sizes (voxel: smallest gray scale unit / pixel with third dimension (cube)) less than 900nm and gives some information about the practical use of a computed tomography system.

In-situ-X-Ray investigation on pressure release during conventional and diffusion soldering

The need for higher operating temperatures in power electronics is driving the research and development on alternative technologies to conventional soldering. One of them is diffusion soldering. Khaja et al. proposed a new approach by printing very thin layers of solder paste. This approach requires a special soldering process to reduce the void content to an acceptable value. Vacuum soldering and overpressure soldering were shown to be appropriate processes [2], [3]. This work investigates both process types with In-situ-X-Ray-analysis. We showed that overpressure reduces the outgassing of voids significantly whereas negative pressure accelerates it. This can be explained by Le Chateliers principle. Furthermore we showed that the solder joints should be cooled immediately after the pressure was reapplied in order to achieve a low void content. The analysis of single voids before and after the pressure change proves that they change their volume according to the ideal gas law. As result of our investigations we conclude that vacuum soldering processes are more suitable for diffusion soldering than overpressure processes.

Online-monitoring of electronic components under temperature stress test

In 2002 a new EU directive called 2002/95/EG (RoHS) caused the electronics industries to change their production lines to lead free soldering processes. However, in some cases they are still using the same electronic components which are not certified for the significant higher temperatures of the lead free soldering process. This causes junk that can only be reduced by placing and soldering critical components separately. Since this is mostly done manually the production costs increase. It is therefore necessary to find out all the critical components and to identify the probability of failure for each of them. Since this task cannot be accomplished by one single company the publicly funded project TDMA was started. The project aims to develop special measurement devices and knowledge about damage mechanisms on electronic components due to high soldering temperatures. In this work a device is presented by which specific properties of electronic components under temperature stress test can be monitored continuously. It features the measurement of resistance, capacitance and inductance of the respective components and forward voltage of LEDs. The device is placed outside of the climate cabinet and controlled by a PC via a RS232 connection.

Packaging for radiation resistant X-ray detectors

Today non-destructive evaluation techniques become more and more important. Consequently, X-ray detectors are suitable tools to get information about specimens. In comparison to the already established scintillation principle, the direct converting method on the basis of semiconductor materials delivers several advantages. Hence, it is necessary to speed this measurement method and develop appropriate packages for these assemblies. In this paper the method of direct converting X-ray line detectors as well as their packaging and relevant aspects are introduced.

X-ray computed tomography for nano packaging - a progressive NDE method

The challenge of nano-packaging requires new non-destructive evaluation (NDE) techniques to detect and characterize very small defects like transportation phenomenon, Kirkendall voids or micro cracks. Imaging technologies with resolutions in the sub-micron range are the desire.

Packaging technologies for (Ultra-)thin sensor applications in active magnetic bearings

We realized ultra-thin and flexible magnetic field sensors based on the Hall Effect in 2 μm thick Bismuth films prepared on commercial flexible double-layer polyimide PCB with a total thickness of 150 μm. These sensors could be potentially applied in active magnetic bearing (AMB) systems. Therefore, here we address reliability aspects of flexible Hall sensors with emphasis on the proper choice of adhesive to mount the sensor to a stator of the AMB. The thermal shock tests in the standard automotive temperature range of -40°C to 165°C as well as the vibration test of the sensor mounted to the stator has proven the sensors stability.

Influences of organic materials on packaging technologies and their consideration for lifetime evaluation

In the recent years the number of applications using organic materials has been significantly increased for electronic devices (e.g. organic LEDs or organic solar cells). This results in stricter requirements to reliable substrate and packaging materials for these applications, especially for flexible substrates. Furthermore, this implies new tasks for the qualifying procedures. One requirement is to characterize the aging of flexible and semiflexible packages concerning bending and twisting. The existing and established test methods have been solely developed for testing rigid substrates and are focused on the influences of the different CTEs (Coefficient of Thermal Expansion) in the electronic package. Adapted mechanical test methods for flexible substrates are not available at the moment. We expect specific damage scenarios which are not characterized with corresponding parameter values. Therefore, we engineered test equipment aiming to accumulate failure data during accelerated aging. These data enable us to develop an aging model for solder joints and comparable technologies. In a subsequent FEM simulation we have to describe a model for different kinds of failure modes. Initial analyses are shown in this paper and shall present an overview on this topic. Furthermore, we investigated a low temperature soldering process for cheap polymeric substrate materials. These materials have a glass transition temperature (Tg) lower than 150°C. The visual appearance is a new topic for electronic packaging, which we have to consider in these investigations.

Packaging development for GaAs X-ray line detectors

Direct converting X-ray line detectors might be a low-cost solution for inline X-ray inspection systems for electronics production and other industries. Possible detector materials are semiconductors in general, in our case GaAs.

X-ray resistant packaging for X-ray line detectors

The challenges of electronics packaging and system integration require new non-destructive evaluation (NDE) techniques during production processes for fast and reliable detecting of small defects like shorts, missing parts or contacts and voids. X-ray techniques like radiography, limited angle tomography and computed tomography are very important methods. Today the common detector principle for X-rays is the so called scintillation detector with a CCD camera behind. But more and more the industry needs fast, reliable and low-cost X-ray systems. Thats why direct converting line detectors are on the engineers focus to be used for “real-time” X-ray scanners. Our paper presents the development of a X-ray resistant detectors module packaging.

Reliability Qualification of Flexible Printed Circuits with Common and New Methods

The use of FFC and FPC will constantly increase in the next years. The development of competitive products can be improved on basis of these technologies. However, the advantages within the range reliability and costs could only be used considering a complete view of the entire process chain efficiency and trend-setting. The complete verification and validating of FFC and FPC require substantial time expenditures. The introduction of new and reliable constructional-technological solutions presently requires too much time. For this reason we gradually compile a concept for the creation of time-efficient testing methods for FFC and FPC of products. We select substrate materials and connecting technologies with the necessary additive materials on the basis of well-known criteria. Duro plastic and thermoplastic materials can be used as substrate materials. In the initial phase we raise data from the results of the standardized accelerated aging procedures. Thus we use thermal test procedures and temperature storage with humidity. We characterize the test structures with destructive and non-destructive examinations. In the following stage we observe test superstructures under self-heating. We characterize the behavior of the test structures again with the well-known procedures. Additionally we measure the length variations in the total structure, brought in by the self-heating. The purposeful overlay and combination of different mechanical, thermal and chemical stresses to the total structure can substantially reduce the test phase in the future. In addition we are continuously acquiring data during the present phase. We designed a structure of test equipment, enabling these measurements. At the end of the running investigations at present we have data to plan the next stage with combined and selected aging procedures