Copyright )^H3 Society of Automotive Engineers, Inc. 740017 Environmental Guidelines for the Designer of Automotive Electronic Components O. T. McCarter1 ABSTRACT This paper describes the climatic, dynamic, and electromagnetic environments in which electronic packages must survive at various locations in the automobile. Previously available climatic data is organized to be use­ ful to the designer. New dynamic information that provides power spectral information for various locations on the automobile is presented. The electromagnetic information includes power line transients, voltage reg­ ulation, and steady-state noise information. THE SENSITIVITY of electronic systems to vehicle environ­ ment is an important consideration in automotive applica­ tions. Both dynamic and climatic environments must be considered carefully and precautions taken to avoid failure under vehicle operating conditions. EFFECTS OF VEHICLE ENVIRONMENT Occasionally one encounters catastrophic failures in the dynamic environments of vibration and shock, including fractures caused by structural and parts failures, and broken wires. More often, one encounters intermittent failures that result in partial but unsatisfactory performance while the environment is present and that disappear when the environ­ ment is removed. Microscopic cracks in printed boards and components or component contamination are often the cause of these failures, and they may be extremely difficult to isolate. Temperature, the most persistent environment, may cause changes in electronic component characteristics and thus result in failures, particularly when the exposure includes cycling between the extremes of temperature. Seal failures or the lack of seals create a sensitivity to contami­ nants such as water, oils, chemicals, and dust, and salt ac­ celerates corrosion. All of these environmental factors can cause serious performance degradation or complete failure. The primary effect of altitude is the reduction of heat trans­ fer efficiency by conduction and radiation, which may re­ sult in characteristic temperature failures. The automobile power system itself must also be considered in a study of this kind since its regulation, electrical noise, and charac­ teristic transients are peculiar to the automobile. All of these environments are important and their effect on electronic systems must be carefully considered in the design phase. It is equally important to verify at the earliest opportunity that the designs offer adequate protection from these environmental factors. Laboratory environmental simulation offers this opportunity. 1 Advance Product Engineering Laboratories, Engineering Staff, General Motors Corp., Warren, Michigan. 2^'J While available automotive environmental information is valuable, little of it is presented with the problems of the electronic designer in view. It is the purpose of this paper to define the environments that are of interest to the elec­ tronic designer and to recommend test methods that rea­ sonably simulate environmental conditions. The environ­ mental definitions are laboratory tools, to be used during the design and verification state of development. They.are not intended to replace the ultimate test of long term opera­ tion under adverse conditions with the electronic systems on the vehicle. The environmental definitions discussed here were measured or derived for the passenger car operating on roadways. While they are comprehensive enough for normal recreational off-road excursions, they do not represent the extreme conditions encountered by vehicles that normally operate in an off-road environment. Location of the elec­ tronic systems on the vehicle has been considered and, where significant environmental differences were encountered, these have been reflected in the definitions and recom­ mended test procedures. ENVIRONMENTAL DEFINITION AND TEST METHODS CLIMATIC ENVIRONMENTS - The cli