QUALITY AND RELIABILITY IN HYBRID CIRCUITSdownloads.hindawi.com/journals/apec/1980/929020.pdf · INTRODUCTION Usersofhybridcircuits expect somedegree of quality fromtheir suppliers,

Electrocomponent Science and Technology, 1980, Vol. 7, pp. 155-1570305-3091/80/0701-0155 $06.50/0

(C) 1980 Gordon and Breach Science Publishers, Inc.Printed in Great Britain

QUALITY AND RELIABILITY IN HYBRID CIRCUITS

R. F. READ

Ministry ofDefence, EQD., GolfRd., Bromley, Kent, U.K.

(Received February 2, 1980)

The quality and reliability of hybrid circuits is examined, with particular reference to the BS9000/CECC systems.It is shown that the capability approval approach developed within the BS9000/CECC systems is appropriate tohybrid circuits where only small quantities of each circuit are produced and the steps involved in obtainingcapability approval are discussed.

1. INTRODUCTION

Users of hybrid circuits expect some degree ofquality from their suppliers, but how do theyquantify their requirements and how do they goabout obtaining them? I suspect there are as manyviews on this subject as there are users.

Quality, is not something that can simply beadded to the component at will. No matter howmany tests the procurement specification invokes,the quality of the component has been establishedduring manufacture and no amount of testing isgoing to change it. The quality can be assessed ormeasured and decisions regarding the component’sability to satisfy a particular requirement can bemade as a result.

Therefore if we wish to influence the quality ofcomponents we must attempt to do it at themanufacturing stage and if we wish to have con-fidence that the required quality is being achieved,it must be demonstrated that the manufacturingenvironment is capable of producing it before wecommit components to expensive quality assurancetesting.

2. THE BS9000/CECC APPROACH TO QUALITY

BS9000 is the national system operating in the UKand is harmonized with the European CECC system.Both are based on the surveillance of manufacturersby an independent organisation, the NationalSupervising Inspectorate.

Each of these systems provides for the followingbasic requirements"

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1) The appraisal and subsequent approval of themanufacturer’s organisation and facilities withrespect to quality.

2) .The Qualification Approval of individualcomponent types to detail specifications or forcertain custom built components, e.g. hybridintegrated circuits, the Capability Approval of aparticular technology.

3) On going quality conformance inspection.

4) Independent surveillance of the manufacturer’sactivities by the National Supervising Inspectorate.

5) ,Certified Test Records ofmeasured performance.

In the UK the National Supervising Inspectorateis involved in all aspects of implementing the BS9000system and its activities can be broken down into 3main areas of involvement"

a) Participation in the work of technical com-mittees in the preparation of the main technical(Generic) specifications of the system. The NSIalso has a responsibility for the checking andacceptance of detail specifications for individualcomponent types written by componentmanufacturers.

b) The appraisal of manufacturers, distributorsand test laboratories wishing to operate within thesystem, to ensure that their organisation, facilitiesand working methods are satisfactory. They alsocarry out regular surveillance thereafter to ensurethat the approval is being adequately maintained.

c) The NSI carry out regular independent audittesting of components manufactured within thesystem. They use their own laboratories for thispurpose using the results of this testing and anysubsequent fault analysis to feed back any necessary

156 R.F. READ

corrective actions, either to the specification systemor to the manufacturer’s activities.

CAPABILITY APPROVAL FOR HYBRIDCIRCUITS

One of the main difficulties in obtaining assurance ofquality for custom-built hybrid circuits usingconventional end product assessment procedures,lies in the low volume non-continuous productionsituation of most hybrid circuit manufacturers.This. means that there are seldom sufficientquantities of any one circuit being produced for along enough period of time for economic statisticalsampling to be meaningful.

Additionally each customer order usually involvesa new design and therefore the design elementbecomes a normal part of the hybrid circuitmanufacturer’s operation.

It is for these reasons that the BS9000/CECCsystems developed the new capability approvalapproach to quality assurance of the custom builtcomponents which shifts the emphasis of qualityassessment from end product to manufacturingprocess.

The concept of capability approval is based on aprecise definition of the boundaries of a capability, adisciplined design and manufacturing activity, ademonstration that the capability is viable and thesubsequent maintenance of the capability by ongoingassessment. This system then sets the scene forquality to a defined standard in manufacture andallows potential customers to negotiate theirperformance requirements with the hybrid circuitmanufacturer in the knowledge that these standardswill be applied automatically. The basic requirementsfor capability approval for hybrid circuits are asfollows:

1) The manufacturer is required to provide adescription of his capability indicating clearly thetechnical boundaries and limiting conditions. Thistakes the form of a capability manual which, whenagreed, becomes the yardstick against which he isinitially assessed and subsequently monitored.The key points to be covered in the capabilitymanual are:

a) Materials and pieceparts the manual mustidentify satisfactory purchase specifications for allcritical materials and must describe the methodsused to verify the suitability of materials forproduction.

b) Design data and layout rules the manualmust make reference to the detailed rules used inthe design and layout of circuits. For example, forthick film hybrid circuits the detailed rules givingappropriate minimum and maximum values mustcover conductor tracks, dielectrics and crossovers,resistors, glaze and/or other protection when used,pattern registration, add-on components and thermalcharacteristics.

c) Flow charts the manual must includedetailed flow charts showing all stages of manufactureand identifying process specifications, workinginstructions and quality control checks.

d) Capability qualifying circuits the manualmust list the test pieces and or circuits which are tobe used to demonstrate the viability of the declaredcapability. These CQC’s must be designed to thedeclared design rules and collectively must cover allthe identified boundaries of the capability.

2) Once the content of the capability manualhas been agreed an appraisal takes place in which theNSI check that the procedures etc. laid down in themanual are in fact implemented and are satisfactory.

3) The manufacturer must then agree a testprogramme with the NSI to demonstrate theviability of his declared capability. This testprogramme will use as test vehicles the capabilityqualifying circuits listed in the manual.

These circuits must be designed using the agreeddesign rules and should include the critical limits ofthose rules. For example, for thick film hybrids thefollowing features will normally be covered:

a) Pads for adhesion testsb) Conductors of min. width at min. spacingc) Resistors of smallest and largest aspect ratio

covering the range of resistor inksd) Largest size resistor dissipating max. rated

powere) Two identical trimmed resistors to demonstrate

matching and trackingf) Smallest size resistorg) A dielectric crossoverh) A solder mounted chip capacitori) An epoxy mounted power transistor chip with

wire bonds.j) An epoxy mounted IC chip (preferably MOS)

with wire bonds.The CQC’s must be packaged in representative

exa.:..ples of the range of packages offered by themanufacturer and in addition to meeting the testrequirements for the design characteristics mustsa:sfy a schedule of environmental and endurance

HYBRID CIRCUITS

tests. In general these are standard tests such assolderability, rapid change of temperature, dampheat, vibration, shock etc., and the endurance coversboth a 160-hour and a 2000-hour period.

4) On completion of the demonstration asatisfactory report results in approval being grantedfor the manufacturers capability within the scopeof his capability manual.

From this point in time the manufacturer isbound by the BS9000/CECC rules governing changes.This means that he cannot make changes to eitherhis capability manual or his manufacturing processeswithout adequate demonstration to the NSI thatthe proposed changes do not reduce the quality ofcomponents. Changes to extend the scope of thecapability can, of course, be recognised by the systemafter the proposed extension has been properlyassessed.

5) In order to maintain his approval the manu-facturer must carry out tests on customer circuitsin accordance with the detail specificationnegotiated with the customer, and in addition mustsubmit CQC’s to:

a) A schedule of short-term environmental andendurance tests, on a lot-by-lot basis

b) A schedule of medium-term environmentaland endurance tests on a periodic basis, normallyevery 3 months, the endurance test is for a 2000-hour period.

c) A schedule of long-term environmental and

157

endurance tests, on a periodic basis, normally everyyear, the endurance test is for an 8000-hour period.These test schedules are specified in the genericspecification for custom built integrated circuits.

6) The manufacturer must accumulate test datafrom maintenance of capability approval testing ofCQC’s to compile certified test records every 6months. The certified test record must give testresults for the current 6-month and 3-year periodsand be available to bona fide customers on request.

4. CONCLUSION

The BS9000/CECC system provides a cost effectivesolution to many of the problems of controllingcomponent activity. By establishing commonterminology, appropriate assessment methods andspecifications it permits economy of scale in themanufacturing industry through the aggregation ofcustomer requirements. Providing an effective qualityassurance support for the equipment industryBS9000/CECC reduces overhead costs and createsan objective data base for circuit and system designers.

ACKNOWLEDGEMENTS

Permission to re-publish this paper is gratefully acknowledged.The paper is copyright (C), Controller HMSO, London, 1979.

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QUALITY AND RELIABILITY IN HYBRID CIRCUITSdownloads.hindawi.com/journals/apec/1980/929020.pdf · INTRODUCTION Usersofhybridcircuits expect somedegree of quality fromtheir suppliers,