Practical Approach for Predicting Reliability of Handheld Devices Based on "Field Stress- Strength" Model

Summary & ConclusionsDifferent forms of Accelerated Life Testing (ALT) are used to predict a product’s reliability in the field over a given period. These tests predict "reliability" or failure rate, which is then used to calculate warranty and cost of service plans. In general, the accuracy of these predictions depends on several factors such as sample size, test parameters, acceleration factors, and most importantly the accuracy of understanding and modeling the real world, field usage profile(s). When it comes to handheld devices, field usage profiles vary greatly between customers and use environments. Factors affecting the use case may include whether the product is used indoors or outdoors, how many shifts per day, how many hours per shifts, is it in a retail environment, manufacturing, warehouse, postal or healthcare, etc.The proposed work builds a framework to predict field failure rate using stress-strength models and develops a "library" of stress profiles for different field use cases, considering factors such as region and/or use environment (retail, postal, etc.) and even particular customer needs. This Stress-Strength model will be referred to as Field Stress-Strength model or FS-S model.Top field failure modes are considered for this research; Display and Touch Panel (TP) cracking is one of the most common field failure modes for handheld devices, often accounting for more than 60% of replaced parts in any given month. Historic field data from various users and strength profiles of the products have been used to define field profiles (stress). Field and service data are used along with minimal testing to construct these profiles. Once field profiles are established, they can be used to predict the failure rate of new products, focusing on the specific failure mode(s) under consideration. Furthermore, a "target" failure rate can be used to establish device specifications. In other words, the strength required to achieve the failure rate goal can be determined. The advantage of this method over traditional ALT is that it requires minimum testing and will therefore save resources and time. Also, it can focus on the vital few failure modes that have a direct impact on customers’ satisfaction.Four-point bending of TP glass was used to measure failure (cracking) strain, then a strength distribution was created. This was used along with historical field data (failure rate) to find stress profile that led to TP/Display cracking. Finally, the Stress profile was used to predict and validate field failure rate for a new generation product that will be used in similar environment. The accuracy of this prediction exceeds 98%