SMART GROUP NEWS-SMART集团新闻
Reports
SMART GROUP VISIT TO ELECTROVERT SMART REFLOW
DAY A large group of SMART Group members visited the Henley premises of Electrovert on 9 May. After the welcome and introduction where Mike Judd emphasised Electrovert's commitment to SMT, a number of papers were presented by the Electrovert team during the morning session. Alan Weston covered the Vapour Phase Reflow process. There is a keen interest in this process again, with the equipment now in third generation. Thermal shock is eliminated using pre-heating as part of the machine. Fluid prices are reducing. Systems that eliminate the secondary blanket ensure that vapour phase uses no CFCs. So the pendulum now appears to be swinging back in favour of vapour phase. Quality, reliability and consistency ensure that this process should be compared against other reflow methods. Phil Atkinson presented the advantages of infra-red reflow soldering of PCBs. He covered recent advances in machines as well as the process. Panel heater design, 'edge heater' technology, controlled convection, exhaust/cooling, computer control, and surface mounted closed loop thermocouple sensors were all described. The importance of evaluating IR reflow systems, with guidelines for selection, were covered in Phil's paper. Geoff Pickles spoke on rework, referring specifically to a sophisticated system that monitors and controls the rework process, automatically develops time/temperature profiles for every component, location and board. Geoff stressed the importance of getting the reflow process right first time, but where rework was necessary the equipment should allow similar temperature profiles with repeatability. Tony Welford took the opportunity to cover briefly the recent advances in SMT cleaning—batch and in-line, alternative solvents to CFCs and the ozone issue, terpenes and the trend towards water cleaning. Tony offered some suggestions on future equipment. Two guest speakers balanced the programme. Gordon Prior of Alpha Metals discussed solder paste and screens. Russ Wood of 3M gave his usual high quality presentation on vapour phase fluids. Time was allowed for questions to all speakers.
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ELECTRONICS BY THE SEASIDE
The small English seaside town of Weymouth played host on 27 June to a gathering of members of the SMART Group. The one-day seminar concerned itself with the current issue of Fine Pitch Technology within the surface mount industry. Presentations were given by Alan Hobby, DEK Printing Machines, on 'Fine Pitch and the Solder Paste Printer', Malcolm Huntley-Thomas, DEK Precision Screen Division, on 'SMT Screens for Fine Pitch Applications', and Bob Hudson of Alpha Metals on 'Fine Line Solder Paste'. All presentations were very informative, and 'well received' was the verdict given by all 20 attendees.
COMPONENT SOLDERABILITY IN ELECTRONICS MANUFACTURE —A DISCUSSION MEETING
National Physical Laboratory, 4 July 1990 The above meeting was organised jointly by the National Physical Laboratory, the Surface Mount Club and the SMART Group. The effectiveness of automated soldering processes depends critically upon the solderability of the two surfaces being joined. In recent months there has been much speculation and debate in the technical press about the fitness-for-purpose of the solderable surfaces of components, in particular surface mount components. Especially at issue are the solderability at goods inwards, the deterioration of solderability during storage, the date coding of components, and the interval between solderability re-tests. This one-day discussion meeting was aimed at providing a forum for component users to give their experience and component suppliers to voice their manufacturing and distribution constraints, in terms of both materials properties and economics, that may limit component quality. The proceedings of the day began with a review of the present scientific understanding of the materials issues that impact upon electronic component solderability. This was given by Colin Lea (NPL). Component solderability comprises both the intrinsic wettability of the terminations with an acceptable electronics-grade flux and the component's ability to withstand the heat of the soldering process. Examples of inadequate heat resistance are the thermal cracking of chip capacitors and the popcorn effect from which some plastic surface mount components can suffer. This meeting, however, considered primarily the phenomenon of wetting and wettability. The majority of component terminations have fusible coatings, normally of tin or tin-lead. The factors that control the wettability of a coating are (i) the oxide thickness, (ii) the morphology and thickness of the interfacial intermetallic phase formed by diffusion between the substrate and its coating, and (iii) the thickness of the remaining fusible coating. Each of these three parameters can, by suitable selective heat treatments, be studied independently. In general terms, the thicker the coating, the better will be the wettability and the longer the solderability will be retained. All parts of the coating initially should be at least 5 μm thick. Under normal storage conditions the intermetallic compound will grow, and reduce the thickness of the fusible coating, very slowly. If, during manufacture, component leads were hot dipped or a plated coating was fused, the molten solder at the corners of leads of rectangular cioss-section can be very thin even if the average thickness is well in excess of 5 μm. Thus, either leads should be circular or the plated coating should be left unfused. The problems associated with using bright plated finishes rather than matt were also discussed. Some components have no fusible coating on their terminations. Generally these are more difficult to wet with solder during assembly, but any deterioration in wettability during ageing is more easily controlled since it is dependent on the cleanliness and the temperature of the storage atmosphere. Species such as hydrogen sulphide, sulphur dioxide, hydrogen chloride, nitrogen dioxide and organic acids at very low levels can have a marked effect on component wettability. The rôle of component lead geometry (in addition to intrinsic surface wettability) in determining the ease of solder fillet formation was also discussed. The design engineer can modify the circuit board pad size and shape but is stuck with a component lead design that is often incompatible with good soldering practice. The problems of goods inward testing of solderability and the usefulness of artificial ageing procedures such as high temperature dry heat and steam were discussed. Two case studies were used by Martin Wickham (Surface Mount Club) to illustrate the crucial aspect of component solderability in electronics manufacture. The following points have great relevance to the debate: (i) Electronics assemblers usually cannot disrupt a production schedule to complain or return goods to their component suppliers if a batch is delivered with poor wettability. They tend to grit their teeth and rework, or change to a more active flux. (ii) There is a trend from RMA towards RA fluxes, to overcome experienced problems of wettability, especially in surface mount. (iii) Reflow soldering of solder paste requires a higher quality of component wettability than does wave soldering because the flux is coming at the metallisation 'from a standing start'. (iv) In a recent Surface Mount Club survey, 55% of electronics assembly companies experienced in in-house manufacture perceived component solderability as being a major problem. Only 12% of component manufacturers acknowledged that there was any problem at all. Ron Neale (RA Neale Associates) talked about quality control and assessment, through goods inward acceptance testing. He has been party to the writing of many of the BS and international standards that relate to solderability of wires, components and circuit boards. For any debate on solderability to be meaningful, tests and measurement methods have to be standardised and, if possible, quantified. The dip and inspect method can be agreed procedurally but the visual assessment is always open to subjectivity. The wetting balance, using a solder bath and more recently a solder globule, gives the opportunity for quantitative measurement. Ron also explained how the choices for accelerated ageing procedures were made. Often these procedures are used in regimes, or for component types, for which they were never intended and are inappropriate. An example of this is a short-term (one hour) steam test during which the solderability can actually improve as the surface cleans. The morning session concluded with an amusing but very salient talk about the experiences of one particular surface mount company. This was given by the Chairman of the SMART Technical Committee, Glyn Jackson (Multitone). Through a concerted programme to improve component and process control, solder joint defects have been reduced from 3000 to 50 ppm on a turnover of half a million components a week. Much of this success is due to improved solderability acceptance testing and component storage. Glyn has questioned all his component suppliers over a number of issues. One issue is the sealing of component reels in airtight bags: those who offered this claimed (quite rightly) a significantly longer shelf life; those who did not offer airtight bags claimed there would be no advantage. Another issue raised was that of date coding: only 6 of his 10 suppliers datecode YY.WW (Year.Week) so as to be understandable to the user. For some manufacturers the code refers to date of manufacture while for others it is the date of taping. Sometimes these dates are a long way apart. The implementation of a YY.WW date of manufacture coding as a requirement for component supply and acceptance would represent a very tangible benefit.#p#分页标题#e#
Reports SMART GROUP VISIT TO ELECTROVERT SMART REFLOW DAY
A large group of SMART Group members visited the Henley premises of Electrovert on 9 May. After the welcome and introduction where Mike Judd emphasised Electrovert's commitment to SMT, a number of papers were presented by the Electrovert team during the morning session. Alan Weston covered the Vapour Phase Reflow process. There is a keen interest in this process again, with the equipment now in third generation. Thermal shock is eliminated using pre-heating as part of the machine. Fluid prices are reducing. Systems that eliminate the secondary blanket ensure that vapour phase uses no CFCs. So the pendulum now appears to be swinging back in favour of vapour phase. Quality, reliability and consistency ensure that this process should be compared against other reflow methods. Phil Atkinson presented the advantages of infra-red reflow soldering of PCBs. He covered recent advances in machines as well as the process. Panel heater design, 'edge heater' technology, controlled convection, exhaust/cooling, computer control, and surface mounted closed loop thermocouple sensors were all described. The importance of evaluating IR reflow systems, with guidelines for selection, were covered in Phil's paper. Geoff Pickles spoke on rework, referring specifically to a sophisticated system that monitors and controls the rework process, automatically develops time/temperature profiles for every component, location and board. Geoff stressed the importance of getting the reflow process right first time, but where rework was necessary the equipment should allow similar temperature profiles with repeatability. Tony Welford took the opportunity to cover briefly the recent advances in SMT cleaning—batch and in-line, alternative solvents to CFCs and the ozone issue, terpenes and the trend towards water cleaning. Tony offered some suggestions on future equipment. Two guest speakers balanced the programme. Gordon Prior of Alpha Metals discussed solder paste and screens. Russ Wood of 3M gave his usual high quality presentation on vapour phase fluids. Time was allowed for questions to all speakers. ELECTRONICS BY THE SEASIDE The small English seaside town of Weymouth played host on 27 June to a gathering of members of the SMART Group. The one-day seminar concerned itself with the current issue of Fine Pitch Technology within the surface mount industry. Presentations were given by Alan Hobby, DEK Printing Machines, on 'Fine Pitch and the Solder Paste Printer', Malcolm Huntley-Thomas, DEK Precision Screen Division, on 'SMT Screens for Fine Pitch Applications', and Bob Hudson of Alpha Metals on 'Fine Line Solder Paste'. All presentations were very informative, and 'well received' was the verdict given by all 20 attendees.#p#分页标题#e#
COMPONENT SOLDERABILITY IN ELECTRONICS MANUFACTURE —A DISCUSSION MEETING
National Physical Laboratory, 4 July 1990 The above meeting was organised jointly by the National Physical Laboratory, the Surface Mount Club and the SMART Group. The effectiveness of automated soldering processes depends critically upon the solderability of the two surfaces being joined. In recent months there has been much speculation and debate in the technical press about the fitness-for-purpose of the solderable surfaces of components, in particular surface mount components. Especially at issue are the solderability at goods inwards, the deterioration of solderability during storage, the date coding of components, and the interval between solderability re-tests. This one-day discussion meeting was aimed at providing a forum for component users to give their experience and component suppliers to voice their manufacturing and distribution constraints, in terms of both materials properties and economics, that may limit component quality. The proceedings of the day began with a review of the present scientific understanding of the materials issues that impact upon electronic component solderability. This was given by Colin Lea (NPL). Component solderability comprises both the intrinsic wettability of the terminations with an acceptable electronics-grade flux and the component's ability to withstand the heat of the soldering process. Examples of inadequate heat resistance are the thermal cracking of chip capacitors and the popcorn effect from which some plastic surface mount components can suffer. This meeting, however, considered primarily the phenomenon of wetting and wettability. The majority of component terminations have fusible coatings, normally of tin or tin-lead. The factors that control the wettability of a coating are (i) the oxide thickness, (ii) the morphology and thickness of the interfacial intermetallic phase formed by diffusion between the substrate and its coating, and (iii) the thickness of the remaining fusible coating. Each of these three parameters can, by suitable selective heat treatments, be studied independently. In general terms, the thicker the coating, the better will be the wettability and the longer the solderability will be retained. All parts of the coating initially should be at least 5 μm thick. Under normal storage conditions the intermetallic compound will grow, and reduce the thickness of the fusible coating, very slowly. If, during manufacture, component leads were hot dipped or a plated coating was fused, the molten solder at the corners of leads of rectangular cioss-section can be very thin even if the average thickness is well in excess of 5 μm. Thus, either leads should be circular or the plated coating should be left unfused. The problems associated with using bright plated finishes rather than matt were also discussed. Some components have no fusible coating on their terminations. Generally these are #p#分页标题#e#http://www.ukthesis.org/ygsslwdx/ more difficult to wet with solder during assembly, but any deterioration in wettability during ageing is more easily controlled since it is dependent on the cleanliness and the temperature of the storage atmosphere. Species such as hydrogen sulphide, sulphur dioxide, hydrogen chloride, nitrogen dioxide and organic acids at very low levels can have a marked effect on component wettability. The rôle of component lead geometry (in addition to intrinsic surface wettability) in determining the ease of solder fillet formation was also discussed. The design engineer can modify the circuit board pad size and shape but is stuck with a component lead design that is often incompatible with good soldering practice. The problems of goods inward testing of solderability and the usefulness of artificial ageing procedures such as high temperature dry heat and steam were discussed. Two case studies were used by Martin Wickham (Surface Mount Club) to illustrate the crucial aspect of component solderability in electronics manufacture. The following points have great relevance to the debate: (i) Electronics assemblers usually cannot disrupt a production schedule to complain or return goods to their component suppliers if a batch is delivered with poor wettability. They tend to grit their teeth and rework, or change to a more active flux. (ii) There is a trend from RMA towards RA fluxes, to overcome experienced problems of wettability, especially in surface mount. (iii) Reflow soldering of solder paste requires a higher quality of component wettability than does wave soldering because the flux is coming at the metallisation 'from a standing start'. (iv) In a recent Surface Mount Club survey, 55% of electronics assembly companies experienced in in-house manufacture perceived component solderability as being a major problem. Only 12% of component manufacturers acknowledged that there was any problem at all. Ron Neale (RA Neale Associates) talked about quality control and assessment, through goods inward acceptance testing. He has been party to the writing of many of the BS and international standards that relate to solderability of wires, components and circuit boards. For any debate on solderability to be meaningful, tests and measurement methods have to be standardised and, if possible, quantified. The dip and inspect method can be agreed procedurally but the visual assessment is always open to subjectivity. The wetting balance, using a solder bath and more recently a solder globule, gives the opportunity for quantitative measurement. Ron also explained how the choices for accelerated ageing procedures were made. Often these procedures are used in regimes, or for component types, for which they were never intended and are inappropriate. An example of this is a short-term (one hour) steam test during which the solderability can actually improve as the surface cleans. The morning session concluded with an amusing but very salient talk about the experiences of one particular surface mount company. This was given by the Chairman of the SMART Technical Committee, Glyn Jackson (Multitone). Through a concerted programme to improve component and process control, solder joint defects have been reduced from 3000 to 50 ppm on a turnover of half a million components a week. Much of this success is due to improved solderability acceptance testing and component storage. Glyn has questioned all his component suppliers over a number of issues. One issue is the sealing of component reels in airtight bags: those who offered this claimed (quite rightly) a significantly longer shelf life; those who did not offer airtight bags claimed there would be no advantage. Another issue raised was that of date coding: only 6 of his 10 suppliers datecode YY.WW (Year.Week) so as to be understandable to the user. For some manufacturers the code refers to date of manufacture while for others it is the date of taping. Sometimes these dates are a long way apart. The implementation of a YY.WW date of manufacture coding as a requirement for component supply and acceptance would represent a very tangible benefit. +++morning starts. On the first day, a basic history and overview of Statistical Process Control was presented. The need for SPC was introduced and the definition of quality discussed. Through a simple bead box experiment, the idea of controllable and uncontrollable variations was illustrated by Zachery Brice. Later in the day, Paddy Regan discussed the organisation involved in co-ordinating an SPC programme, and the importance of both management commitment and employee involvement for successful implementation. The second day began with Paddy Regan outlining the different types of control charts that can be used, depending on the type of data that can be measured during the process. Various examples of charts were shown and discussed. Dr Eamon Murphy followed with a presentation on experimental design, which in theory should minimise the 'tweaking' on a process and identify the optimal process settings. He also discussed a number of the statistics packages available. Daithi Fallon of Digital Equipment in Galway presented a case-study of a designed experiment which involved just one day's work to optimise a rework system. The attendees were then divided into three groups, and each group was presented with a problem. Each group was then asked to define its problem, the process steps involved and then design an experiment to identify the main possible causes of the problem through the different process stages. This proved a most interesting and informative exercise for most of the attendees who had no experience in this area, particularly when it came to presenting the results. The workshop adjourned early on the first day to a tour of the facilities at the National Microelectronics Research Centre, where attendees were able to see state-of-the-art microelectronics facilities including silicon fabrication, IC test, failure analysis, computer-aided design, II1-IV semiconductor processing, and interconnection and packaging facilities consisting of high pincount IC packaging, SMT and thickfilm/hybrid circuit processing, environmental test equipment and IC package characterisation. The tour was followed by a reception given by the NMRC during which attendees were addressed by Cian O Mathuna of SMART Group-Ireland and Bob Willis, chairman of the SMART Group.#p#分页标题#e#
