Combined Temperature and Vibration Testing for Wire Bond Interconnections in Harsh Environment Electronics

In an attempt to simulate for purposes of laboratory testing of electronic components the high-intensity sound fields encountered in the proximity of modern rocket and jet aircraft, the Armour Research Foundation has developed a convenient laboratory device, designated the “ARF High-Intensity Sound Chamber.” The ARF Chamber is simple to construct, calibrate, and operate. It utilizes readily obtainable components, including a small commercial loudspeaker driver, and is approximately 6 × 8 × 10 in., with a test chamber size of 6 × 6 × 6 in. It is estimated that a similar sound chamber could be constructed and instrumented for about $600. Calibrations have been made with audio-oscillator and “white noise” inputs; sound pressure levels in the order of 155 db are obtainable. Results of preliminary tests on electron tubes, sensitive relays, and pressure switches are included in the paper. This information is particularly interesting, as test results show some effects not obtained by vibration testing. Thus, it appears that high-intensity sound tests serve as a useful and valid supplement to vibration testing of airborne electronic components. The work was sponsored by WADC.

Escalation of the expense of gold has resulted in industry interest in use of copper as alternative wire bonds interconnect material. Copper wire has the advantage of lower price and comparable electrical resistance to gold wire. In this paper, 32-pin copper-aluminum wire bond chip scale packages are aged at three types of environment conditions separately. Environmental conditions included: 200°C for 10 days, 85°C and 85% RH for 8 weeks and −40°C to 125°C for 500 thermal cycles. The resistances of the wire bond are obtained every 24 hours for 200°C environment, every 7 days for 85C/85RH environment and every 5 days (50 thermal cycles) for the thermal cycling environment. A leading indicator has been developed in order to monitor the progression effect of the different thermal aging condition on the package and prognosticate remaining useful life based on the resistance spectroscopy. The Cu-Al wire bond resistance has been measured using a modified Wheatstone bridge. It has been shown previously that precise resistance spectroscopy is able to offer the failure of a leading indicator prior to the traditional definition of failure. The prognostic health management is qualified to be an efficient and accuracy tool for assessment of the remaining life of the wire bond. The ability to predict the remaining useful life of Cu-Al wire bond provides several advantages, including increasing safety by providing warning ahead of time before the failure.

This paper presents an investigation of true downhole dynamic conditions through improved testing methods and a new measurement-while-drilling (MWD) tool. Shock loads may cause severe damage to bottomhole assembly (BHA) components. Consequently, characterizing the shock loads and analyzing their distribution within drilling tools produces information for the design process that can improve tool reliability and efficiency. The difference between shock loads and traditional dynamics is rarely discussed within the drilling industry, so this paper first introduces a mathematical description of shocks. Experimental shock and vibration tests are used to investigate the shock and vibration loads experienced by full-scale downhole drilling tools. The test rigs for this effort enable testing of full-scale drilling tools as long as 10 m and a maximum weight of 2 tons. Testing of entire drilling tools, and the emulation of downhole conditions, enables realistic dynamic loading and an analysis of the interaction of tool internal components. These results are not possible when testing single components on a vibration table. During the tests, acceleration sensors positioned at several locations on the outside of the tool body measure the shock amplitude. Simulation models enable analysis of the load distribution within the tested tool. Depending on the simulation results, the reliability of all internal components can be ensured. If necessary, further design improvements are initiated. The simulation models are validated and improved with data from experimental modal analyses of the test rigs and the tested tools. Identifying uncertain parameters for complex dynamics simulation models is a particularly challenging task. Results from the shock tests are compared to the simulation results for additional validation because shock loads, in contrast to typical vibrational loads, are transient. Shock and vibration tests also serve to evaluate the capabilities and limits of current MWD tools in terms of sampling rate and sensor range. A newly developed MWD tool for dynamics measurement was tested, evaluated, and optimized using this testing process. The tests and simulations enable optimization of drilling tools for shock and vibration loads. In contrast with the limitations of historical measurements, enhanced dynamics-measurement capabilities with higher sampling rates and extended sensor ranges provide increased data quality and better characterization of downhole shock and vibration loads. This improved understanding of drilling dynamics loads leads to reliability enhancement and cost optimization by reducing shock and vibration-related tool failures.

A nondestructive method for load rating of bridges without structural properties and plans

The GEDI Mission will employ three lasers systems developed, built, and tested by NASA Goddard Space Flight Center. We discuss the flight level Thermal Vacuum (TVAC) and vibrational qualification testing each unit must pass.

This paper presents the results of an experimental research program to develop a novel type of assembly-level vibration test. The design of a multimodal test fixture, which simulates the high-frequency (100–2000 Hz) dynamic characteristics of a MARINER spacecraft structure, is described. Data obtained in research vibration tests with an electronic assembly mounted in the multimodal fixture indicate that the novel testing technique results in a more realistic and more uniform high-frequency vibration environment than conventional tests utilizing rigid fixtures. The paper presents guidelines for designing multimodal fixtures and discusses means of utilizing these fixtures in future spacecraft assembly-level vibration test programs.

As the semiconductor packaging industry continues to lower its manufacturing costs, concerted efforts in the supply chain focusing on using copper (Cu) as wire bond interconnects has intensified to an unprecedented level. In our previous study we showed that Cu wire has significantly higher wire sweep compared to gold (Au) wire after molding. In this study, wire sweep performance was further evaluated using various wire lengths and diameters of both Au and Cu wires in plastic ball grid array (PBGA) packages. In general, wire sweep increases with wire length increase and reduces with increasing wire diameter. It was accepted that wire sweeps are influenced by wire length, wire diameter, and density of wire which can be further explained with the cantilever deflection formula. In this study, a screening design of experiment was conducted on 18µm copper wire using thermally enhanced PBGA package to identify key molding parameter factors affecting wire sweep during mold encapsulation process. Based on JMP analysis, pellets preheat time, package pressure, and transfer speed are found to be the key factors to reducing the wire sweep percentage. Moreover, it was also found that the interaction of pellet preheat time and package pressure is also a significant factor to reduce overall Cu wire sweeping.

Interconnecting to aluminum- and copper-based semiconductors (electroless-nickel/gold for solder bumping and wire bonding)

The intermittent fault (IF) in electrical systems is considered to be one of the most challenging problems to tackle. At present, there remains a lack of understanding as to the mechanism of IF. Therefore, this letter is focused on the characteristics of IF in electrical connectors under vibration environment. Based on the mechanical structure of a certain kind of electrical connector, a dynamic model is constructed to analyze how its contact resistance varies under vibration environment. In addition, a vibration test rig intended for electrical connectors and a contact resistance acquisition system are developed. Under vibration environment, experiments are conducted on electrical connectors with IF injected. According to the results obtained from both sweep-frequency and fixed-frequency vibration test, some conclusions are summarized regarding the frequency, amplitude, and phase characteristics of the IF in electrical connectors, which is conducive to improving the understanding as to the fundamental mechanism of IF caused by vibration stress.

In the electronic industry, there is currently a renewed interest in the study of the failure of BGA package and socket solder joints under mechanical stressing, specifically shock and vibration. This means that an analyst now needs to know the proper modeling and test procedures to use in order to better tackle the problem of solder joint reliability under shock and vibration loading. In this paper, an effort has been made to collate the best known methods associated with vibration testing of electronic components mounted on printed circuit boards.

Electronics in harsh environments may be subjected to extended periods of simultaneous high temperature and vibration and stored for prolonged periods of time prior to and during deployment. Damage accrued during the storage and prior usage may reduce the remaining useful life of the electronic system during deployment. Methods for assessment of accrued damage under simultaneous stresses are scarce. Test to failure data has been measured to study the effect of simultaneous thermal and vibration loadings on the reliability of BGA components. Two groups of pristine and isothermally aged components have been tested at both room temperature and 125°C while simultaneously being subjected to vibration loads. The transient response of printed circuit boards under the overlapping stresses has been characterized. Damage accrued under overlapping stresses has been investigated using physics-based leading indicators of damage. The leading indicators are state vectors based on optically measured strains and deformation, resistance spectroscopy and phase sensitive detection. An extended Kalman filter (EKF) is employed to predict remaining useful life (RUL) of the BGA components. A particle swarm optimization (PSO) technique, has been used to robustly demonstrate and quantify the repeatability of the resistance spectroscopy measurements and the accompanying prognostic algorithms.

Design of Head Expander (HE) for environmental vibration testing components with a required test frequency range has become very important, because it is an interface between electrodynamics vibration shaker and test specimen. The HE subjected to resonant and anti-resonant frequencies due to limitations of mass/stiffness properties. The random vibration and harmonic analysis of existing Head Expander was carried out and validated with tested results in the present work. The proposed new features Head Expander is designed by introducing three different hole-patterns which accommodates the different configurations of work pieces for vibration testing. Modal analysis, random vibration and harmonic analysis were carried out using generalized finite element software, ANSYS. The GRMS values of proposed HE design are compared with GRMS values of NAVMAT P-9492 work and found satisfactory.

A new research method based on vibration testing for the vibration fatigue of FRP was proposed in this paper. Through the testing on a closed-loop controlled vibration fatigue test system, the vibration fatigue phenomenon of typical carbon-fiber-reinforced plastic (CFRP) cantilevered laminate specimens was carefully studied. Moreover, a method based on the frequency response function was proposed to monitor the fatigue damage accumulation of specimens. On the basis of that, the influence factors that affect the vibration fatigue life of CFRP were experimentally studied. The influence of amplitude probability distribution of the vibration load spectrum on the fatigue life was deeply explored. Compared with Gaussian random vibration, the non-Gaussian random load has a significant impact on the vibration fatigue life of CFRP. The experimental results also showed that the magnitude of power spectral density (PSD) has a significant effect on the vibration fatigue life of specimens. For Gaussian vibration load, the frequency bandwidth almost has no effects on the vibration fatigue life of CFRP. However, for non-Gaussian vibration load, it has a great impact on the fatigue life. When PSD magnitude and frequency bandwidth are constant, the root mean square (RMS) is proportional to the vibration fatigue life of composites.

Structure bolt tightening force and loosening monitoring by conductive MXene/FPC pressure sensor with high sensitivity and wide sensing range

Copper wire bond remains a challenge especially on bond pads with sensitive pad metallization. Extensive work and analysis are needed at the onset of the packaging development phase to meet the right level of manufacturability and reliability requirement. Wire bond related issue is not uncommon even after qualification and after years in high volume manufacturing. The process development gets even tougher for finer wire diameter, bond pads with less than 1μm aluminum thickness and of higher via density structure. A workable wire bond process window is needed upfront. Key is to have a window defined to balance between pad cratering and lifted ball bond due to the harder property of the copper wire. Wire bond process optimization commonly focus around bond time, bond force and bond power (USG). Other factors generally evaluated for copper wire bonding include incoming bond pad cleanliness, bonding pad surface oxidation, wire oxidation during EFO and forming gas flow rate. A lesser known variable, die attach, is often overlooked in packaging or gold to copper wire conversion. Die attach material out gassing at cure is a common hypothesis whenever there is bond pad surface contamination issue. But with the advancement in technology and new material development, out gassing risk is low if the material is cured per the supplier recommendation. Therefore, investigation on weak bond is generally focused more on the wire bond process and incoming bonding pad condition rather than the die attach material. In this paper, investigation on non stick and copper wire bond was carried out. A well defined copper wire bond process on sensitive bonding pads is developed using statistical approach in the form of design of experiment (DOE) and response surface methodology (RSM). Surface analysis methodology using SEM, EDS and AES were also utilized to check for bond pad contamination. To understand deeper into the issue and mechanics of the failure, process mapping and brainstorming sessions have also been carried out. Variables involving wafer saw, pre-wire bond plasma, different batches of wafers, die attach bond line thickness and tilt variation have all been studied thoroughly. Eventually, the root cause of copper wire bond issue been identified to be die attach material related. A strong correlation has been found between lifted wire and the die attach material modulus. There is no more lifted ball concern after changing of the die attach material to a material of a suitable modulus. There is no significant difference in the die attach bond line thickness, coverage and voids among others, comparing with the original die attach material. All the wire bond responses including pad cratering, Al-Cu intermetallic (IMC), wire pull and ball shear have been validated to have no issue at a larger sample size. Reliability assessment in the form of preconditioning, temperature cycling and bias HAST have also passed with no sign of interfacial mechanical failure or test failure. The modulus of elasticity of the die attach material is important and must be a key consideration in copper wire qualification. The elasticity of the material changes from room temperature to copper wire bonding temperature. A low modulus at the bonding temperature can cause wire bondability problem such as lifted ball bond due to ultrasonic power loss during ball bonding. Therefore, selection of a die attach material with a suitable range of modulus of elasticity is critical in the integrity of copper wire bonding.