Advances in Electronic Circuit Packaging: Volume 5 Proceedings of the Fifth International Electronic Circuit Packaging Symposium sponsored by the University of Colorado, EDN (Electrical Design News), and Design News, held at Boulder, Colorado, August 19–2 PDF
Preview Advances in Electronic Circuit Packaging: Volume 5 Proceedings of the Fifth International Electronic Circuit Packaging Symposium sponsored by the University of Colorado, EDN (Electrical Design News), and Design News, held at Boulder, Colorado, August 19–2
Vol. 5 Lawrence L. Rosine Advances in Electronic Circuit Packaging Proceedings of the Fifth International Electronic Circuit Packaging Symposium sponsored by the University of Colorado, EDN (Electrical Design News), and Design News, held at Boulder, Colorado, August 19–21, 1964 A Publication of Cahners Publishing Company, lnc. ADVANCES IN Volume 5 ELECTRONIC CIRCUIT PACKAGING Proceedings of the Fifth International Electronic Circuit Packaging Symposium sponsored by the University of Colorado, EDN (Eiectrical Design News), and Design News, held at Boulder, Colorado, August 19-21, 1964 Edited by Lawrence L. Rosine, Editor, EDN SPRINGER SCIENCE+BUSINESS MEDIA. LLC 1965 Library of Congress Catalog Card Number: 62-2203 ©Copyright 1965 Springer Science+Business Media New York Originally published by Rogers Publishing Company, lnc. in 1965 Softcoverreprint ofthe bardeover 1st edition 1965 ISBN 978-1-4899-7295-8 ISBN 978-1-4899-7307-8 (eBook) DOI 10.1007/978-1-4899-7307-8 All rights reserved No part of this publication may be reproduced in any form without written permission from the publisher Foreword This fifth volume of Advances in Electronic Circuit Packaging contains information assembled by specialists who are pushing to new frontiers in the field of packaging. The firms represented by these gentlernen are typical of the major electronic industries. Cover age of all the facets of electronic packaging, earthbound hardware to orbiting systems, is included in these articles. While the success of such a conference as the International Electronic Circuit Pack aging Symposium is certainly due in great part to the excellence of the papers presented during the sessions, credit must also be given to the untiring efforts of a group that receives little prominence. They are the members of the Program Selection Committee. These experts in the field, most of whom have presented papers at previous symposia, spend many hours of their own time discussing, selecting, rejecting, and rediscussing the papers submitted for possible use. This is no easy task. Almost all of the papers submitted are good. Some good papers were undoubtedly rejected so that the sessions could be kept to the allotted time. Some of the rejected papers have appeared over the past months in the packaging section of EDN. Others have appeared, in whole or part, at other technical sessions. The process of selection of these papers is not a simple one. Abstracts of the papers are reviewed by each member of the selection committee. The paper is rated individually by a numbering system. The numbers for each paper are totaled, and a meeting of the committee is called. As the committee members are active in the field, they are able to objectively review each paper on its merit. A final decision is then reached based on this discussion and the number of points each paper receives. The man-hours spent on this selection far exceed the total hours of the symposium. This is done to assure the attendees of the symposium - and the readers of the proceedings - that they are obtaining the very Iatest, comprehensive information available in the field of electronic circuit packaging. Therefore, we deem it fitting that the members of the Program Selection Committee should be Iisted as the true editors of Advances in Electronic Circuit Packaging. Gien Boe, Cahners Pubfishing Company D. A. Beck, Bendix Research Laboratories G. E. Gless, University of Colorado J. R. Goodykoontz; Space Technology Laboratories, Inc. E. J. Lorenz, IBM Corporation *R. C. Mayne, Jet Propulsion Labaratory *E. C. Neide!, Sandia Corporation W. J. Prise, Lockheed Missiles & Space Co. *M. I. Ross, The Mi/ton Ross Company J. C. Rubin, Eastman Kodak Co. H. J. Scagnelli, Bell Telephone Laboratories, Inc. L. S. Shuey, Sprague Electric Co. T. A. Telfer, General Electric Co. Lawrence L. Rosine Editor, EDN *Indicates new members since the fifth symposium. üi Contents ÜEORGE R. DALLIMORE Encapsulants for Electronic Packaging . PAUL SHERLOCK Use of Radiation-Cross-Linked Materials for Encapsulating and Terminating Devices . 13 c. E. NEIDEL Encapsulating with Loose Microballoons 21 EDMUND C. DECKER Packaging Concept for a Miniature Low-Light-Level TV Camera 28 R. E. KLEIN AND J. GAMMON The Heat-Sink Module . 43 E. I. MooRE AND L. M. ScHNEIDER Producibility Norms for Electronic System Packaging 58 ÜILBERT R. REID Development of Packaging Techniques for a 960-Bit Plated-Wire Memory 63 DONALD SHANER AND FRANK L. JENNINGS Packaging Computer Circuitry for Space Application - A Two-Part Compendium 72 ROBERT F. ZECHER A Cost and Performance Analysis of Encapsulation by Transfer Molding 87 H. B. BELLAND G. A. DOYLE Packaging of Miniature Diode Assernblies . 98 FREDERIC J. LOCKHART Transfer Molding of Silicone Compounds for Environmental Protection of Elec- tronic Modular Systems . 106 T. J. WILLIAMS AND R. R. ROGERS A Feasibility Study in Miniaturized Packaging 119 RosERT C. MAclNTYRE AND HERBERT WINSKER Interconnection and Organization of Functional Electronic Blocks 133 LAWREN(;E D. HUNTERAND ROBERT W. KoRB Designing for Multilayer Cireuits . 141 FREDERICK L. KOVED A Flexible Module Concept for Electronic Box Design 157 R. c. PAULSEN AND w. K. SPRINGFJELD A High-Frequency Multiple-Signal-Conductor Transmission Line 165 WILLIAM L. THIBODEAU High-Frequency Interconnections. 178 STEVE ZELENCIK Interconnection Systems 188 EARLE R. BUNKER, IR. Substitution of a Printed Conductor Ring Harness for a Conventional Cable Har- ness on the Mariner Series Spacecraft. 201 V vi Contents HoMER E. HENSCHEN Design of Connectors for Electronic Packaging 214 S. BoNIS, R. JACKSON, AND B. PAGNANI Mechanical and Electronic Packaging for a Launch-Vehicle Guidance Computer 226 N. SHAPIRO, P. SMITH, AND M. GENSER Standard Package for Microcircuits . 242 ALLAN V. PAINTER AND REGINALD A. ALLEN Semiconductor Circuits and Modular Packaging 249 E. F. UBER, w. D. FULLER, AND A. J. DOMENICO A Packaging Evaluation of a Five-Bit Adder . 266 F. F. STUCKI Radiation Effects in Epoxies Used as Encapsulants for Electronic Packages . 278 H. G. FRANKLAND Designing a High-Voltage Power Supply for a Space Radar System . 284 Encapsulants for Electronic Packaging ÜEORGE R. DALLIMORE Lockheed Missile and Space Company Sunnyvale, California Many types and classes of embedding compounds are available for encapsulating electronic packages. For a particular application, an embedding compound must be selected that meets the design parameters, the electrical, mechanical, thermal, and environmental requirements. The factual property data necessary for such selection and the comparative advantages and dis advantages of the available encapsulating and potting compounds are tabulated and discussed. The problern of selecting a specific encapsulant for a particular electronic package currently being used in an aerospace application is presented. The matehing of the design parameter, the electrical, mechanical, thermal, and environmental requirements to the electrical, physical, and thermal properties of the available embedding materials is described. INTRODUCI'ION MANY TYPES OF EPOXY, silicone, and polyurethane casting, coating, and foam-in-place materials are available for the protective encapsulation of electronic circuits. Little information is avail able on the comparative advantages and disadvantages of these encapsulants for electronic circuit packaging. Which encapsulating material to use for a particular electronic device is a problern facing many electronic packaging engineers. Technical property data on encapsulants are widely scattered among vendor's literature, military specifications, company specifications, technical journals, and technical reports by the various users of these materials. It is the intent of this paper to tabulate and classify the technical property data and the comparative advantages and disadvantages of the available encapsulating materials and to show how this information was used in the selection of an encapsulant for the environmental protection of a particular electronic package. SELECfiON OF ENCAPSULANT In most electronic packaging applications the encapsulant has the triple function of a structural member, electrical insulator, and heat-conducting medium, and must maintain these properties through many adverse environments. The selection of encapsulants to perform these important functions is an important part of electronic packaging. Encapsulants should be selected on the basis of a detailed technical analysis of the electrical, mechanical, thermal, and environmental requirements. The technical analysis should be conducted, and the en capsulant selected, during the initial stages of the packaging design. The actual Iayout of the package should be begun with the electrical, mechanical, thermal, and physical properties of the selected encapsulant firmly in mind. Since the electrical, mechanical, thermal, and physical properties of the encapsulants are all temperature dependent, a detailed thermal analysis of the circuit is especially important. The results of this thermal calculation or measurement will determine whether highly filled 2 George R. Dallimore high-thermal-conductivity encapsulants are to be considered, or if lighter-weight materials such as syntactic foams, unfilled resins, or foam-in-place materials can be used. The thermal environments in which the electronic package must operate and be stored are also important considerations when selecting encapsulants. Shrinkage of the resin during eure along with differences in coefficients of expansion of the resin and components cause severe internal stresses to be set up in electronic packages during thermal cycling andfor storage. The resultant stresses have been known to cause cracking of the encapsulant material or cracking of sensitive components such as diodes, capacitors, and resistors encased in glass. Thermal cracking of the encapsulant can usually be solved by eliminating metal inserts and hardware or by reinforcing the resin in the stressed area or by using more resilient encapsulating materials. The mechanical properties ofthe encapsulant arealso quite important since the encapsulant is usually used as the only structural support for the components. The encapsulant must be rigid and strong enough to provide this support during handling and installation, and under vibration and mechanical shock environments. Because of their high mechanical and structural properties, epoxy resins have been used almost exclusively for the protective encapsulation of electronic devices for the aerospace industries. At temperatures below 85°C the electrical properties of most encapsulants are sufficient for the majority of low-voltage electronic devices operating below one megacycle. Above 85°C TABLEI Epoxy Resin--Unfilled, Rigid Properlies Unit Typical value Physical Specific gravity 1.0-1.2 Hardness Shore D >80 Moisture absorption % 0.1--{).3 Electrical Volume resistivity ohm-cm 1015-1018 Dielectric strength volts/mil 450 Dielectric constant 2.8-3.5 Dissipation factor 0.005--{).010 Mechanical Flexural strength psi 18 X J03 Tensile strength psi 9-12 X J03 Elongation % 5 Compressive strength psi !8-20 X 103 Modulus of elasticity psi 4-5 X 105 Thermal Conductivity cal/sec/cm/'C/cm 4 x w-• Expansion in./in./'C 65 x w-• Heat resistance ·c up to 200 Relative Appraisal of Properries Advantages Disadvantages Transparent Poor thermal shock resistance Excellent electricals High stress on components High mechanicals High shrinkage Excellent adhesion Poor impact resistance Low moisture absorption Medium coefficient of expansion Fair thermal conductivity Not repairable Encapsulants for Electronic Packaging 3 particular attention must be paid to the degradation of electrical properties with temperature, especially with the semiresilient and flexible epoxies and polyurethane foams. With high gain andjor high-frequency circuits, particular attention must be paid to possible interelement coupling effects caused by high-dielectric-constant encapsulants. Low-dielectric-constant foams have had widespread application in high-frequency circuitry. In the encapsulation of high-voltage devices, particular attention must be paid not only to the dielectric strength of the encapsulant but also to its adhesion to and compatibility with other insulating materials such as sleeving and wire insulations in the package. Encapsulants for high-voltage applications must also be capable of being vacuum cast to eliminate internal voids which can cause breakdown or corona at high altitudes. Consideration must also be given to the various environments to which the finished package may be exposed. Most electronic packages have to contend with water in the form of high humid ity, actual immersion, or salt-spray resistance. Fortunately, practically all the solid encap sulants have sufficient moisture resistance so that seldom is a choice of encapsulant based solely on the differences in moisture absorption. Foamed plastics are not inherently resistant to moisture, and special coatings or containers should be used. Vacuum resistance is very dependent upon temperature and length of exposure. Encapsulants containing solvents, plasti cizers, and nonreactive diluents have very poor vacuum and radiation resistance. Rigid highly filled (mineral filler) resins and silicone rubbers exhibit the best radiation resistance. TABLE TI Epoxy Resin-Unfilled, Semiftexible Properlies Unit Typical value Physical Specific gravity 1.0-1.2 Hardness Shore D 50-80 Moisture absorption % 0.75 Electrical Volume resistivity ohm-cm 1012-1014 Dielectric strength volts/mit 350 Dielectric constant 4.0-5.0 Dissipation factor Mechanical Flexural strength psi 12 X 103 Tensile strength psi 3-4 X 103 Elongation % 25 Compressive strength psi 7-10 X 103 Modulus of elasticity psi 1 x 10• Thermal w-• Conductivity cal/secjcm/'C/cm 4 x w-• Expansion in./in./'C 90-too x Heat resistance 'C 100 max Relative Appraisal of Properlies Advantages Disadvantages Good thermal shock resistance Poor electricals (above 75'C) Transparent Poor mechanicals (above 75'C) Fair electrical (to 75'C) High coefficient of expansion Fair mechanical (to 75'C) Low moisture absorption Some repairability Fair thermal conductivity 4 George R. Dallimore SPECIFIC ENCAPSULATING MATERIAlS Epoxy Resins Epoxy resins, because of their overall excellent electrical, mechanical, and physical proper ties, are the most widely used encapsulating resins for electronic packaging. The ability to modify almost any property through the use of selected fillers, flexibilizers, modifiers, and curing agents, have given epoxies the versatility to meet almost every environmental requirement imposed on electronic packaging materials. The various epoxy resin systems can be sub divided into seven major classes, each class being generally characterized by its specific gravity and hardness. Tables I-VII present typical property data and generalized advantages and disadvantages of these materials. Handling and curing properties such as viscosity, pot life, eure temperature, eure time, and exotherm have been deliberately left out of the tables since there are available within each class resin systems with varying handling properties and eure schedules. Foams Rigid polyurethane foams with densities from 2 to 20 lb/ft3 are used extensively for en capsulating low-voltage, low-proper-dissipating electronic devices. For most applications TABLE m Epoxy Resin-Unfilled, Flexible Properties Unit Typical value Physical Specific gravity 1.0-1.2 Hardness Shore 65A-50D Moisture absorption % Electrical Volume resistivity ohm-cm 10'o-J012 Dielectric strength volts/mil 275-350 Dielectric constant 5.4-9.4 Dissipation factor 0.15~.3 Mechanical Flexural strength psi Tensile strength psi 4 X 103 Elongation % 100 Compressive strength psi Modulus of elasticity psi Thermal Conductivity cal/sec/cm/"C/cm 4 x 1o-• Expansion in./in./"C I50 x w-• Heat resistance 'C 75' max Relative Appraisal of Properfies Advantages Disadvantages Excellent thermal shock resistance Poor electricals (above 75 'C) Transparent Low mechanicals Fair electricals (to 75'C) Poor heat resistance Fair thermal conductivity Highest coefficient of expansion Repairable High dielectric constant Low stress on components High dissipation factor
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