Correlation of a Sinusoidal Sweep Test To Field Random Vibration

This paper presents a method for transferring the measured field random vibration into a sinusoidal sweep test by using the damage equivalence technique. This requires the fatigue damage generated in the sinusoidal sweep to be equivalent to the damage during the desired lifetime in the field operation. Based on this approach, a correlated lab-test specification, including the vibration level and test duration, can be determined according to the field random load input, the desired product life goal of a product, and the material/structural properties. If a generic test specification is required without knowing the material/structural properties, an approximate approach is proposed based on some engineering assumptions. In this paper, the development of a test specification for an automotive bracket is demonstrated as an application example.

Isolation Ratio and Particle Performance Measurement of a SMIF System

This paper discusses the performance evaluation of a SMIF (Standard Mechanical Interface) system. A two-chamber experimental system is used with one chamber providing the test atmosphere of the cleanroom and the other providing the test atmosphere of the minienvironment. The cleanroom atmospher can be varied by adjusting the amount of particles injected into the chamber. Particle concentration ranges from 1,000/ft-3 to 10 million/ft3 can be created in the chamber to simulate different cleanroom conditions. The atmosphere of the second chamber is maintained at Class I or better equivalent by means of a self-powered ultra-low penetration air (ULPA) filter blower unit. By means of this system, the ability of the SMIF system to isolate the contaminants in the cleanroom atmosphere from the minienvironment atmosphere was measured. In addition, the particles added to the wafer during wafer cassette handling by the SMIF-Arm were also measured by a wafer scanner. The results indicate that the SMIF system tested is capable of providing extremely high isolation ratios in terms of its ability to isolate the cleanroom atmosphere from the atmosphere of the minienvironment. Isolation ratios in excess of 1 million to 1 or better have been measured. The measured particle per wafer per pass (PWP) numbers were generally around 0.02 or less for most wafers, with the average at 0.0118.

Minimum Sampling Time/Volume for Liquid-Borne Particle Counters and Monitors

A particle counter is an instrument that measures particles in all the fluid passing through its sensor, and a particle monitor measures particles only in a portion of the fluid. For liquid with an ultralow particle concentration, particles may not disperse uniformly in the liquid. Therefore, the concentrations may vary significantly from measurement to measurement if the sample volume is not large enough. To achieve the same precision, a minimum sampling time or minimum sample volume for a particle instrument needs to be specified. A Poisson distribution was used to describe the distribution of particle counts. Testing included a series of particle concentration measurements. Minimum sampling time or sample volume at a given average concentration with different error levels was determined for selected commercial particle instruments. At the same flow rate, a particle monitor always requires a longer sampling time than a particle counter to achieve a specific precision for a given concentration. The minimum sampling time also varies among instruments because of the difference in sample volume in which the particles are counted. Experiments with a particle monitor have been conducted to thest the changes in average particle concentration and the standard deviation at different operating conditions.

A Strategy to Integrate the 'Tailoring' and 'Stimulation' Test Philosophies

This paper considers the benefits and liabilities of the tailoring and stimulation test philosophies. It introduces a hybrid strategy to link the tailoring and stimulation test philosophies into an integrated philosophy with implementation examples. A methodology to create generic environmental requirements through Weibull analysis of historical databases is presented. The implications in the hybrid philosophy are discussed along with reliability demonstration considerations. Examples of product requirements are provided for vibration and thermal environments.

Mars Pathfinder Spacecraft, Lander, and Rover Testing in Simulated Deep Space and Mars Surface Environments

The Mars Pathfinder (MPF) spacecraft was built and tested at the Jet Propulsion Laboratory during 1995 and 1996. MPF was launched December 4, 1996, and successfully landed on Mars on July 4, 1997. The testing program required that the mission hardware be subjected to both deep space and Mars surface conditions. A series of tests were devised and conducted from January, 1995, to July, 1996, to study the thermal response of the MPF spacecraft to the environmental conditions to which it was to be exposed during the cruise phase (on the way to Mars) and the lander phase (landed on Mars). In addition, several tests were conducted to study the thermal characteristics of the Mars rover. Sojourner, under Mars surface environmental conditions. Several special test fixtures and methods were devised to simulate the required environmental conditions. Creating simulated Mars surface conditions was a challenging undertaking since the Mars surface is subjected to diurnal cycling between -20°C and -85°C, with wind speeds to 20 m/sec, occurring in an 8 torr CO2 atmosphere. This paper describes the MPF test program conducted at JPL to verify the MPF thermal design.

Rinsing: A Critical Process in Contamination Removal

The rinsing process of silicon wafers is normally carried out in an "overflow" bath in which water flows past the wafers at average velocity of 1 cm/s. But the velocity is zero at the wafer surface. The efficiency of rinsing is limited by the rate at which contaminants diffuse away from the silicon surface and into the flow stream. This paper reports the improvement in rinsing efficiency gained by repeating a 1-min cycle of first allowing the contaminants to diffuse into the stagnant layer and then "dumping" the rinse tank to remove most of the contaminated stagnant layer. A further 10-fold improvement in rinsing efficiency per rinse cycle can be achieved by spinning the wafer and using centrifugal force to remove a greater fraction of the stagnant layer. This allows the complete removal of soluble contaminants with a 20-fold reduction in water usage compared to present immersion techniques.

Characterizing Electrodynamic Shakers as a Two-Port Network

An electrodynamic shaker is modeled as a mixed electrical/mechanical system with an experimentally derived two-port network characterization. The model characterizes the shaker in a manner that the performance of the shaker with a mounted load (test item and fixture) can be predicted. The characterization depends on the measurements of shaker input voltage and current, and on the acceleration of the shaker armature with several mounted loads. The force into the load is also required and can be measured directly or inferred from the load apparent mass.

On Generic Vibration Criteria for Advanced Technology Facilities: with a Tutorial on Vibration Data Representation

The design of vibration-sensitive advanced technology facilities generally involves considerable attention to structural and mechanical aspects. In most cases, the vibration control measures contribute significantly to a facility's cost. The selection of a vibration criterion for use in design is an important step in the design process. Many process equipment manufacturers have provided tool-specific criteria, and the literature contains several forms of "generic" criteria. Unfortunately, there is no standardization in either tool-specific or generic criteria, and considerable confusion can arise, often due to the forms of data representation used. This paper first reviews some of the relevant fundamentals of signal processing, then uses experimental data to develop a tool-specific vibration criterion for an optical microscope. Two dissimilar approaches to generic criteria are discussed, and their signal-processing requirements are examined. They are compared with a manufacturer's published vibration criteria for a projection aligner. Recommendations are given for future development of tool-specific criteria.

Instrument Design For Sub-PPB Oxygenated Contaminants Detection in Semiconductor Processing

This paper describes a technique for measuring trace quantities of oxygen and moisture contaminants present in a semiconductor and/or containerless processing environment. Monatomic negative oxygen ions, O-, formed by electron dissociative attachment through interaction with the molecular oxygen and water, are measured to infer the presence of the contaminants. This technique exploits the fact that the cross section for the reaction is greatly enhanced at the resonant energy. The device built to demonstrate this technique combines a small gridded electron ionizer with a conventional mass spectrometer. The concentrations of oxygen have been measured using the method of standard additions by diluting O2 in N2. The lowest detection limit obtained was 1.2 kHz (O- count rate) at a concentration of 1010 corresponding to 0.1 ppb. Sensitivity calculations for detecting moisture, and electron and ion trajectory modeling using the SIMION program are presented. The detection of trace quantities of water vapor was attempted. The difficulties with handling water in the experiments are also described.

Characterizing the Commercial Avionics Thermal Environment for Field Reliability Assessment

Defining environmental loading is often the most uncertain part of the electronics reliability calculation. This paper demonstrates a practical methodology to measure and characterize the dynamic thermal history of the commercial airplane environment. To reduce irregular field thermal cycles, an algorithm is presented that preserves key information necessary for viscoplastic solder fatigue analysis. As an example. the IPC solder model will be used to evaluate 20 termination leadless ceramic chip carriers on nonconstrained printed wiring boards. This methodology will enable more realistic thermal fatigue reliability assessments and acceleration test specifications.