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Rework of Electronic Assemblies Qualifiable Processes for Rework Guidelines Rework of Electronic Assemblies Qualifiable Processes for Rework German Electrical and Electronic Manufacturers’ Association Rework of Electronic Assemblies Published by: ZVEI - Zentralverband Elektrotechnikund Elektronikindustrie e. V. German Electrical and Electronic Manufacturers’ Association PCB and Electronic Systems Division Lyoner Strasse 9 60528 Frankfurt am Main, Germany Editor: Dr Christoph Weiß, ZVEI Phone: +49 69 6302-437 E-mail: [email protected] www.zvei.org/pcb-es Authors: Thomas Lauer, Airbus DS Electronics and Border Security Peter Fischer, Batiloy Company for Soldering Technology Sebastian Bechmann, Christian Koenen Harald Grumm, Ersa Jörg Nolte, Ersa Helge Schimanski, Fraunhofer Institute for Silicon Technology Franz Leitenstern, Martin Franz-Josef Schoeferle, Rohde & Schwarz Messgerätebau Conrad Wagenbrett, Wagenbrett Dr. Lothar Weitzel, Würth Elektronik Dr. Helmut Schweigart, Zestron Europe Janos Tolnay, Zevac Stefan Penzenstadler, Zollner Electronics Michael Zimmerer, Zollner Electronics Florian Gruber, Zollner Electronics November 2017 This document may be reproduced free of charge in any format or medium, includ- ing in part, provided it is used correctly and not in a misleading context. The ZVEI copyright must be visible and the title of the document must be specified. A free copy of the document in which ZVEI material is used must be made available. The ZVEI assumes no liability for the content. Content 1 Introduction 6 2 General Aspects 7 2.1 Definition of rework and repair 7 2.2 The line process as a reference 7 2.3 Norms, standards and guidelines 9 2.4 Flux interaction "No-clean - but..." 12 2.5 Parameters 14 2.6 Acceptance requirements 16 2.7 Printed circuit board 17 2.8 Components 27 2.9 MSL-Moisture Sensitivity Level 27 2.10 Thermal profiling 29 2.10.1 Tools and sensor positioning 29 2.10.2 Methodology of profile determination 29 2.11 The nth soldering process 33 2.12 Heat transfer 34 2.13 Process flows 35 2.13.1 When a component "must" - "can" - "must not" 35 be reworked 2.13.2 Sequence of component replacement 36 2.13.3 Detailed process flow 39 2.14 Device technology 40 2.14.1 Hand soldering devices 40 2.14.2 Quasi-stationary rework systems 44 2.15 Devices - Systems - Concepts 45 2.15.1 Semi-automatic hot gas rework system 45 2.15.2 Automatic hot gas rework system 49 2.15.3 Automatic IR rework system 52 3 Manual Soldering - Trials and Findings 56 3.1 Proven equipment within the trial series 56 3.2 Two typical disciplines of the manual soldering area 56 3.2.1 Desoldering, resetting and 56 manually re-soldering of passive components 3.2.2 Processing of PQFP components 57 3.3 Findings on manual soldering 57 4 Findings from the R+R Studies 60 4.1 Thermal profiles (target-actual) 60 4.2 Printed circuit board as the dominant component 63 4.3 Component specifications, ordered according to their 66 complexity 4.3.1 Two-pole, passive components 66 4.3.2 Two-pole, passive ferrite choke with high 66 heat demand 4.3.3 Components with flat Gullwing connections 67 4.3.4 SMT connectors in mixed SMT-THT technology 67 4.3.5 Classical ball grid array designs 67 4.3.6 Array connectors (BGA pin-out) 69 4.3.7 BGA socket 69 4.4 Possible effects at assembly level 70 4.5 Multiple solder stress – visual/cross-section analysis 70 4.5.1 Assemblies after multiple solder stress 71 in visual inspection 4.5.2 Assemblies after multiple solder stress in 74 cross-section analysis 4.5.3 Assessment of the multiple solder stress influence 79 4.6 Reballing 81 4.6.1 Motivation 81 4.6.2 General course of the reballing process 81 4.6.3 Devices - systems - concepts 82 4.6.4 Balling stencils 91 4.6.5 Reballing / 91 recommendation for the process sequence 4.7 Stencil and process technology 92 4.7.1 Rework stencils 92 for printing on printed circuit boards 4.7.2 Rework stencils for printing on components 94 4.7.3 Rework stencils for dipping components 95 4.7.4 Process engineering 97 5 Neuralgic Points for Consideration 99 5.1 Faults - cause index 99 5.2 Electrochemical migration (ECM) 117 5.2.1 Preconditions for the emergence of 117 electrochemical migration 5.2.2 Formation mechanism 118 5.2.3 Consequences of electrochemical migration 119 5.2.4 Qualification of residues after rework 120 5.3 Overview of test results 123 6 Conclusion/Outlook 126 6.1 Reliability 126 6.2 Thermal processes 127 6.2.1 Rework/component process preference table 127 6.2.2 Repair/component process 129 7 Closing Remarks 131 8 Corporate and Research Partners 132 9 Bibliography 133 10 Glossary 135 1 Introduction Keywords such as process or machine In the event of doubt, the user must, capability, six-sigma approaches, flat-rate together with his client, weigh up for his zero-defect strategies or lean are initially project whether or not his process is a repair oriented primarily to the high-throughput as defined in chapter 2.1. line and mass soldering processes, leaving little acceptance for (seemingly) useless, At the same time, relevant norms, standards non-value-adding processes such as rework and guidelines for the implementation of or repairing electronic flat assemblies. high-quality, reproducible rework or repair will be presented. Particularly within specific sectors, any additional rework or even repair step is The content of this guide is based on the regarded as a neglected additional disci- prior knowledge and individual experience pline not worthy of discussion. of all members of the WG, and on the other hand the findings of the test assemblies of If these reasons for a strictly negative atti- ZVEI-WG R+R (especially created for this tude are exclusively due to the fact that purpose). these exceptional corrective steps are a sup- posedly expensive measure, this might seem Specific risks and neuralgic points within an acceptable justification. Unfortunately, the entire process design are presented and the fundamental quality of these supple- recommendations for implementation are mentary measures is often questioned with- given on the basis of the respective param- out having considered the procedures used eters of the procedures and processes. in detail. Irrespective of the solder alloys to be used, These uncertainties about the assessment the effects of lead-free rework and repair and design of any necessary rework or repair with SnAg3.0Cu0.5 solders (SAC305 sol- steps are nurtured by the supposedly poor ders) are primarily discussed in the present initial situation with regard to established case, but the findings on soldering pro- process principles for safe process design. cesses with other alloys can be carried over at suitable process temperatures in the light The aim and purpose of the ZVEI Rework of the thermal load capacity of the assem- and Repair (R+R) Working Group (WG) is blies/components. to present the understanding gained in the form of an industry recommendation with The user of the guide will be given a sum- regard to the chances and risks of rework mary of all important factors for the safe and repair processes and, if necessary, to implementation of R+R processes in the sensitise them to specific needs. form of a decision or processability matrix. The guide is intended to enable both cus- tomers and manufacturers to identify possi- ble process limitations and process specifics and to help them develop a more consist- ent perception, need-oriented acceptance and improved understanding of the topic of rework and repair. This guide first presents the basic consider- ations for rework and repairing assemblies. Only rework will be covered in the guide, as its aim and purpose is to ensure the con- formity of the finished product with draw- ings and specifications. 6 2 General Aspects 2.1 Definition of rework and repair Only too easily are non-original value- Repair: adding processes such as rework and repair Restoring the operability of a defective classified as repairs and not separately con- article in a way which does not ensure the sidered. complete consistency of the article with the corresponding drawings or specifications. However, a closer look is needed to properly assess the underlying procedures and con- Irrespective of which type of corrective cepts of rework, repair or modification (as a action is chosen, some basic questions must special case) if required. first be clarified: • Is the corrective measure only an A compact definition of the respective unscheduled transitional measure or is methods is provided by the IPC-T-50J [1], in there a risk of it becoming routine? which the terms are described as below. • How effective is the measure? • Are there any qualitative restrictions on Rework: the change? Rework of a non-conforming article with • Are there restrictions on reliability? original or equivalent processing in a way • Is it possible to apply an additional which ensures the complete consistency of measure at all? the article with the corresponding draw- • Are suitable ESD protection measures ings or specifications (could also definitely implemented to protect the components include a component replacement). and assemblies? • Are there any restrictions with respect to Modification: moisture-sensitive components (MSL)? Revision of the functionality of a product • Are cleanliness, proper handling and suf- to meet new acceptance criteria. Changes ficient employee qualification ensured? are generally necessary to take account of design changes, which are made in draw- ings, by alteration orders, etc. Changes are to be made only with the express permission and accompanied by the detailed documen- tation in the applicable documents. 2.2 The line process as a model In order to meet the individual thermal The objectives of an optimised reworking requirements and general conditions for step using the rework system are: the reworking of electronic assemblies, the • Thermal profile stability and characteristic soldering processes to be applied must first in line with the (reflow) line process be defined and assessed.
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