1、BRITISH STANDARD BS CECC 00808:1996 Harmonized system of quality assessment for electronic components Guidance document: Use and application of plastic encapsulated devices ICS 31.020BSCECC00808:1996 This British Standard, having been prepared under the directionof the Electrotechnical Sector Board,
2、 was published underthe authority of the Standards Board and comes intoeffect on 15 August 1996 BSI 11-1998 The following BSI references relate to the work on this standard: Committee reference EPL/47 Draft for comment 94/208150 DC ISBN 0 580 26112 3 Committees responsible for this British Standard
3、The preparation of this British Standard was entrusted to Technical Committee EPL/47, Semiconductors, upon which the following bodies were represented: Federation of the Electronics Industry GAMBICA (BEAMA Ltd.) Ministry of Defence National Supervising Inspectorate (BSI Product Certification) Societ
4、y of British Aerospace Companies Limited The following bodies were also represented in the drafts of the standard, through subcommittees and panels: British Telecommunications plc UK Optical Sensors Collaborative Association Amendments issued since publication Amd. No. Date CommentsBSCECC00808:1996
5、BSI 11-1998 i Contents Page Committees responsible Inside front cover National foreword ii Foreword 2 Text of CECC 00808 3BSCECC00808:1996 ii BSI 11-1998 National foreword This British Standard has been prepared by Technical Committee EPL/47 and is identical with CECC 00808:1996, Guidance document:
6、Use and application of plastic encapsulated devices, published by the European Committee for Electrotechnical Standardization (CENELEC) Electronic Components Committee (CECC). The British Standard which implements the CECC Rules of Procedure is BS 9000 General requirements for a system of electronic
7、 components of assessed quality Part 2:1996 Specification for the national implementation of the CECC system. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British
8、 Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, theCECC title page, pages 2 to 6 and a back cover This standard has been updated (see copyright date) and may have had amendments incorp
9、orated. This will be indicated in the amendment table on theinside front cover.GUIDANCE DOCUMENT DOCUMENT GUIDE LEITFADEN CECC 00808 February 1996 ICS 31.020.140 Descriptors: English version Guidance document: Use and application of plastic encapsulated devices (to be completed) (to be completed) Th
10、is CECC Specification was approved on 1995-11-28. This CECC Specification exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has th
11、e same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CENELEC European Com
12、mittee for Electrotechnical Standardization Comit Europen de Normalisation Electrotechnique Europisches Komitee fr Elektrotechnische Normung Central Secretariat: rue de Stassart 35, B-1050 Brussels 1996 Copyright reserved to CENELEC members Ref. No. CECC 00808:1996 ECECC00808:1996 BSI 11-1998 2 Fore
13、word This CECC Guidance Document was prepared by CLC/TC CECC/WG GB. The text of the draft was submitted to the formal vote and was approved by CENELEC as CECC00808 on 1995-11-28. The following dates were fixed: Contents Page Foreword 2 1 Reasons for considering the use of Plastic Encapsulated Device
14、s 3 2 Considerations when using Plastic Encapsulated Devices 3 3 Reliability of Plastic Encapsulated Devices 4 4 Quality Assurance issues 6 5 Conclusions 6 latest date by which this document has to be implemented at national level by publication of an identical national standard or by endorsement (d
15、op) 1996-09-01 latest date by which the national standard conflicting with this document have to be withdrawn (dow) 1996-09-01CECC00808:1996 BSI 11-1998 3 1 Reasons for considering the use of plastic encapsulated devices There are many reasons for considering the use of plastic encapsulated devices
16、(PED) as opposed to non-PED, e.g. ceramic, metal can, hermetic, glass etc. 1.1 Many electronic functions are only available in plastic encapsulated devices. For a long time military applications were the main reason for the development of new electronic components. Packages suitable for military and
17、 space applications therefore always existed. During the past fifteen years development of new components has been mainly due to non-military applications (consumer products, computers and telecommunications. Packages are essentially plastic and military applications only an eventual second step. Th
18、e use of only non-PEDs limits the number of functions available to the designers. This is especially true for the very complex integrated functions. 1.2 P.E.D are often smaller than the equivalent cavity device. This is specially true for the discrete components and the non complex integrated functi
19、ons. 1.3 P.E.D. are generally less expensive than a cavity device with the same functions particularly for mass production. This is due to their manufacturing process being more cost effective and their greater production volumes. There is also in general more competition between the suppliers of pl
20、astic devices because there are more manufactures. This is particularly true for less complex functions. The price improvement becomes less important when the functions are very complex. 1.4 The use of plastic encapsulated devices results in less expensive equipment. If we take the example of Integr
21、ated Circuits The number of components in a given design is lower due to the greater number of complex functions available. Each Integrated Circuit is usually less expensive. The Printed Circuit Board (PCB) surface area will have a greater component density as the same electronic function will use f
22、ewer and smaller packages resulting in smaller PCB surface area. The area of the PC board is an important factor of its cost. As a result of the above Logistic Support Cost need not be adversely affected by the use of PEDs with acceptable reliability in the required environment. 1.5 They generally h
23、ave a better resistance to shock and vibration than cavity devices. Therefore using plastic encapsulated devices should improve Logistic Support Costs in the considered environment provided that acceptable reliability is demonstrated. In addition the use of PEDs may improve the performance with resp
24、ect to the technical capabilities such as volume and weight of electronic equipment as well as their resistance to shock and vibration 1.6 The thermal expansion coefficient of plastic more closely matches that of most PC boards. 2 Considerations when using plastic encapsulated devices Usage of plast
25、ic encapsulated devices raises some specific problems. 2.1 Power dissipation should be considered with respect to the technology used. 2.2 Non hermeticity of the package may give a greater failure rate under high humidity conditions. However, there has been rapid progress in achieving consistent imp
26、rovement targets for plastic packages (in excess of 1000 hours of Highly Accelerated Stress Testing HAST) as a result of: Improved resins. Protection of the chips (multi-coating with silicon nitride). 2.3 Technology investigation is more complex. This is due to four main reasons: The quality of the
27、plastic compound is critical and difficult to check by the component manufacturer before using the material, and evidence is much more difficult for the component user to check. There is no non destructive test method available for plastic encapsulated devices comparable to the fine and gross leak t
28、est used for cavity packaged devices. However, test methods such as acoustic tomography (not yet defined) and X-ray could be used. The quality and repeatability of the process control exercised during the encapsulation is also very difficult for the component user to check.CECC00808:1996 4 BSI 11-19
29、98 The rapid evolution in the technologies used (materials, equipment and processes) in association with the high pressure on prices, induces many process changes which increase the users difficulty of having knowledge of the processes in current use. 2.4 Where power dissipation is important the use
30、 of plastic encapsulated devices may cause a higher temperature of the semiconductor resulting in: A limitation of the temperature range of the devices. An increase of the failure rate of the devices. 2.5 Non hermeticity of the device means that its life duration may be limited in severe environment
31、s. 3 Reliability of plastic encapsulated devices The reliability analysis concerns two aspects of the reliability, the failure modes and the failure rates (See Paragraph 4 Quality Assurance Issues). 3.1 Failures due to mechanical stresses on the die a) Cause: Mechanical forces applied on the die dur
32、ing the manufacturing process of the component. b) Failure mechanism: An initial limited crack of the die with no functional impact is generated during the moulding process. It is generally created by forces resulting from the pressure of the compound and the thermal expansion coefficient difference
33、 between the die material (silicon) and the plastic material during the cooling sequence and progresses due to external reasons (thermal cycling, vibrations, shocks), until it reaches an active part of the silicon die. c) Improvement methods: Improvement in the matching of thermal coefficients of th
34、e moulding material and the silicon die. Better control, by computer simulation of the mechanical forces generated during the moulding process. This results in: optimum shape of the die and the lead frame. optimum positioning and shape of the injection channels in the moulding tooling. d) Present si
35、tuation: The results of the temperature cycling tests show that this type of failure is no longer a problem when the appropriate improvements have been implemented. 3.2 Failure due to moisture ingress a) Cause: The fact that the plastic encapsulated device is not heremetic allows moisture to migrate
36、 inside the package. The main corrosion results from presence of active ions e.g. chloride combined with moisture. b) Failure mechanism: If, after the moulding and the lead bending, a separation exists between the lead frame and the plastic at the point the lead frame enters into the plastic the con
37、taminants and/or moisture migrate for instance along the leads and the wires. A 3 volt potential generated by Gold/Aluminium interface in the presence of humidity and active ions triggers an electrolytic metal attack (EMA) reaction of the metallic bond and its destruction. c) Improvement methods: Ne
38、w plastic compounds have been developed with less than 1ppm active ions. Lead frame design has been studied to improve the adhesion of the plastic to the lead frame and provide necessary geometrical clearances. The moulding process parameters are optimised to improve the chemical and physical charac
39、teristics of the compound. A post moulding cure sequence is used to achieve this improvement. Improved quality of the die passivation (double or triple passivation) provides an enhanced protection of the silicon against contamination agents coming from the compound. The use of halide products during
40、 the equipment manufacturing process is avoided (a special concern is the flux used in soldering process). The risk of corrosion is minimised by reducing the inter-metallic electromotive force. d) Present situation: The plastic encapsulated devices are not hermetic, but the moisture migration proces
41、s has been reduced by a large factor (more than25 and very likely more than 50).CECC00808:1996 BSI 11-1998 5 A modern plastic package design using the latest manufacturing process can withstand more than 7000 hours of 85 C/85% RH THB which allows its use in long term applications under standard avio
42、nics conditions. The corrosion process is accelerated by temperature, pressure and applied voltage. The highly accelerated stress test (HAST) provides high pressure temperature and humidity and a high acceleration factor. This allows the qualification of manufacturing batches quickly on a sampling b
43、asis. 3.3 Failure modes due to assembly on board process. 3.3.1 Long term corrosion a) Cause: Migration in the plastic compound of active ions due to chemical processes applied during board assembly. This concerns cleaning and particularly fluxing before soldering. b) Failure Mechanism: See para 3.2
44、 b. c) Improvement methods: This is the responsibility of the component user. His manufacturing process must be free of any liquid (or vapour) carrying active ions. 3.3.2 “Popcorn” (cracks of the plastic surface) a) Cause: Moisture present inside the plastic package can generate vapour under high te
45、mperature conditions. The problem is restricted to equipment manufacturing processes which submerge the circuit board and device in solder. Typically this means surface mounted devices (SMD) and not through hole mounted PEDs which are thermally remote by virtue of the lead length. b) Failure mechani
46、sm: During a thermal shock the vapour has no time to leak out of the package and generates high pressure in the compound. Cracks are generated at the surface of the body of the device or internally (the latter are not detectable by visual inspection). This occurs generally during the soldering seque
47、nce. c) Improvement method: Moisture sensitive PED delivered in labelled (Reference JEP113) dry packaging and quoting the appropriate moisture sensitivity level (Reference JESD22-A112) should be used within the “floor life” period, after the packaging is opened. When this time is exceeded, or the PE
48、D are extremely moisture sensitive, then baking must be applied just before the soldering sequence to eliminate moisture from inside the body of the device. References: 3.4 Other potential failure mechanism applicable to plastic packages. a) Delamination at the interface(s) between lead frame/die pa
49、ddle/chip surface, particularly with copper alloy lead frames (because of their greater TCE than Kovar, with respect to the lower TCE of silicon). b) Die-attach quality with large die, particularly with copper alloy lead frames. c) Stress cracking of the moulded plastic. d) Wire-sweep in high lead-count, fine pitch packages. e) Reduced physical strength of very thin packages. f) Wire-bond shear due to TCE difference between plastic and IC, especially with large area ICs. g) Due to poor heatsink flatness or screwi
