EN 60068-3-13:2016
(Main)Environmental testing - Part 3-13: Supporting documentation and guidance on Test T - Soldering
Environmental testing - Part 3-13: Supporting documentation and guidance on Test T - Soldering
IEC 60068-3-13:2016 provides background information and guidance for writers and users of specifications for electric and electronic components, containing references to the test standards IEC 60068-2-20, IEC 60068-2-58, IEC 60068-2-69, IEC 60068-2-83, and to IEC 61760-1, which defines requirements to the specification of surface mounting components. This first edition cancels and replaces IEC 60068-2-44:1995 and constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - information for lead-free solders are added; - technical update and restructuring.
Umgebungseinflüsse - Teil 3-13: Ergänzende Unterlagen und Anleitung zur Prüfung T - Löten
Essais d'environnement - Partie 3-13: Documentation d'accompagnement et guide sur les essais T - Brasage
L'IEC 60068-3-13:2016 donne des informations de base et des lignes directrices aux rédacteurs et utilisateurs de spécifications relatives aux composants électriques et électroniques, avec des références aux normes d'essai IEC 60068-2-20, IEC 60068-2-58, IEC 60068-2-69 et IEC 60068-2-83, ainsi qu'à l'IEC 61760-1 qui définit les exigences pour la spécification des composants pour montage en surface. L'IEC 60068-3-13 annule et remplace la deuxième édition de l'IEC 60068-2-44. Cette norme constitue une révision technique. Ce document inclut les modifications techniques majeures suivantes par rapport à l'IEC 60068-2-44: - ajout d'informations sur les brasages sans plomb; - mise à jour technique et restructuration.
Okoljsko preskušanje - 3-13. del: Podporna dokumentacija in navodilo za preskus T: Spajkanje
Ta del standarda IEC 60068 podaja dodatne informacije in navodila za avtorje in uporabnike specifikacij za električne in elektronske komponente, ki vsebujejo reference za preskusne standarde IEC 60068-2-20, IEC 60068-2-58, IEC 60068-2-69, IEC 60068-2-83 in IEC 61760-1, ki določajo zahteve za specifikacije komponent za površinsko montažo.
General Information
Relations
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Okoljsko preskušanje - 3-13. del: Podporna dokumentacija in navodilo za preskus T: SpajkanjeEssais d'environnement - Partie 3-13: Documentation d'accompagnement et guide sur les essais T: BrasageEnvironmental testing - Part 3-13: Supporting documentation and guidance on test T: Soldering25.160.01Varjenje, trdo in mehko spajkanje na splošnoWelding, brazing and soldering in general19.040Preskušanje v zvezi z okoljemEnvironmental testing01.110L]GHONHTechnical product documentationICS:Ta slovenski standard je istoveten z:EN 60068-3-13:2016SIST EN 60068-3-13:2016en01-december-2016SIST EN 60068-3-13:2016SLOVENSKI
STANDARDSIST EN 60068-2-44:20011DGRPHãþD
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 60068-3-13
September 2016 ICS 19.040
Supersedes
EN 60068-2-44:1995
English Version
Environmental testing - Part 3-13: Supporting documentation and guidance on Test T - Soldering (IEC 60068-3-13:2016)
Essais d'environnement - Partie 3-13: Documentation d'accompagnement et guide sur les essais T - Brasage (IEC 60068-3-13:2016)
Umweltprüfungen - Teil 3-13: Ergänzende Unterlagen und Anleitung zur Prüfung T: Löten (IEC 60068-3-13:2016) This European Standard was approved by CENELEC on 2016-06-17. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CENELEC member.
This European Standard 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 CEN-CENELEC Management Centre has the same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung CEN-CENELEC Management Centre: Avenue Marnix 17,
B-1000 Brussels © 2016 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 60068-3-13:2016 E SIST EN 60068-3-13:2016
The following dates are fixed: • latest date by which the document has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 2017-03-17 • latest date by which the national standards conflicting with the document have to be withdrawn (dow) 2019-06-17
This document supersedes EN 60068-2-44:1995.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent rights.
Endorsement notice The text of the International Standard IEC 60068-3-13:2016 was approved by CENELEC as a European Standard without any modification. In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 60068-2 Series NOTE Harmonized as EN 60068-2 Series. IEC 60749-20 NOTE Harmonized as EN 60749-20. IEC 61190-1-1 NOTE Harmonized as EN 61190-1-1. IEC 61191 Series NOTE Harmonized as EN 61191 Series. IEC 61192 Series NOTE Harmonized as EN 61192 Series. IEC 61760-4 NOTE Harmonized as EN 61760-4. SIST EN 60068-3-13:2016
Normative references to international publications with their corresponding European publications
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here: www.cenelec.eu
Publication Year Title EN/HD Year
IEC 60068-2-20 2008
Environmental testing -
Part 2-20: Tests - Test T: Test methods for solderability and resistance to soldering heat of devices with leads EN 60068-2-20 2008
IEC 60068-2-58 -
Environmental testing -
Part 2-58: Tests - Test Td: Test methods for solderability, resistance to dissolution of metallization and to soldering heat of surface mounting devices (SMD) EN 60068-2-58 -
IEC 60068-2-69 -
Environmental testing -
Part 2: Tests - Test Te: Solderability testing of electronic components for surface mounting devices (SMD) by the wetting balance method EN 60068-2-69 -
IEC 60068-2-83 -
Environmental testing -
Part 2-83: Tests - Test Tf: Solderability testing of electronic components for surface mounting devices (SMD) by the wetting balance method using solder paste EN 60068-2-83 -
IEC 61760-1 -
Surface mounting technology -
Part 1: Standard method for the specification of surface mounting components (SMDs) EN 61760-1 -
IEC 62137-3 -
Electronics assembly technology -
Part 3:
Selection guidance of environmental and endurance test methods for solder joints EN 62137-3 -
IEC 60068-3-13 Edition 1.0 2016-05 INTERNATIONAL STANDARD NORME INTERNATIONALE Environmental testing –
Part 3-13: Supporting documentation and guidance on Test T – Soldering
Essais d'environnement –
Partie 3-13: Documentation d'accompagnement et guide sur les essais T – Brasage
INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE
ICS 19.040
ISBN 978-2-8322-3359-7
– 2 – IEC 60068-3-13:2016 IEC 2016 CONTENTS FOREWORD . 4 1 Scope . 6 2 Normative references. 6 3 Terms, definitions and abbreviations . 6 3.1 Terms and definitions . 6 3.2 Abbreviations . 7 4 Overview . 7 4.1 Factors influencing the formation and reliability of solder joints (ability to be soldered) . 7 4.2 Physics of surface wetting . 8 4.3 Quality and reliability of solder joints . 10 5 Component soldering – Processes . 10 5.1 General considerations . 10 5.1.1 Components' ability to be soldered . 10 5.1.2 Soldering processes . 12 5.1.3 Soldering defects . 12 5.1.4 Geometrical factors which may influence the soldering result . 12 5.1.5 Process factors . 12 5.1.6 Material factors . 12 5.2 Solder . 13 5.3 Grouping of soldering conditions . 13 5.4 Ability to be soldered . 13 5.5 Moisture sensitivity of components . 13 5.6 Relation between storage time/storage conditions and solderability . 14 5.6.1 Natural and accelerated ageing . 14 5.6.2 Oxidation . 14 5.6.3 Growth of intermetallic layers . 14 5.6.4 Effect of ageing to wetting characteristics . 14 5.6.5 Test conditions for accelerated ageing . 15 5.7 Place of soldering tests in testing . 16 6 Soldering tests . 17 6.1 General . 17 6.2 Solder . 18 6.3 Fluxes . 18 6.4 Test equipment . 18 6.5 Evaluation methods . 18 6.5.1 Criteria for visual inspection . 18 6.5.2 Criteria for quantitative evaluation of the wetting characteristic . 19 6.5.3 Special cases . 19 6.6 Acceptance criteria . 19 7 Soldering tests – Methods . 19 7.1 General principles . 19 7.2 Survey of test methods . 19 7.3 Bath test . 22 7.4 Reflow test . 23 7.4.1 With/without solder land . 23 SIST EN 60068-3-13:2016
IEC 60068-3-13:2016 IEC 2016 – 3 – 7.4.2 Selection of solder paste (flux system and activity grade) . 23 7.5 Soldering iron test . 23 7.6 Resistance to dissolution of metallization and soldering heat . 23 7.6.1 General . 23 7.6.2 Limitations . 23 7.6.3 Choice of severity . 24 7.7 Wetting balance test . 24 7.7.1 General . 24 7.7.2 Test methods available . 25 7.7.3 Limitations . 25 8 Requirements and statistical character of results . 25 Bibliography . 27
Figure 1 – Sessile drop of solder on oxidised copper . 8 Figure 2 – Sessile drop of solder plus flux on clean copper . 9 Figure 3 – Sessile drop equilibrium forces . 9 Figure 4 – Typical soldering processes . 12 Figure 5 – Soldering tests for devices with leads . 21 Figure 6 – Soldering tests for SMDs . 22
Table 1 – Solder process groups . 13
– 4 – IEC 60068-3-13:2016 IEC 2016 INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________
ENVIRONMENTAL TESTING –
Part 3-13: Supporting documentation and guidance on Test T – Soldering
FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees. 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services carried out by independent certification bodies. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications. 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 60068-3-13 has been prepared by IEC technical committee 91: Electronics assembly technology. This first edition cancels and replaces IEC 60068-2-44:1995 and constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: – information for lead-free solders are added; – technical update and restructuring.
IEC 60068-3-13:2016 IEC 2016 – 5 – The text of this standard is based on the following documents: FDIS Report on voting 91/1345/FDIS 91/1356/RVD
Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. A list of all parts in the IEC 60068 series, published under the general title Environmental testing, can be found on the IEC website. The committee has decided that the contents of this publication will remain unchanged until the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to the specific publication. At this date, the publication will be • reconfirmed, • withdrawn, • replaced by a revised edition, or • amended.
– 6 – IEC 60068-3-13:2016 IEC 2016 ENVIRONMENTAL TESTING –
Part 3-13: Supporting documentation and guidance on Test T – Soldering
1 Scope This part of IEC 60068 provides background information and guidance for writers and users of specifications for electric and electronic components, containing references to the test standards IEC 60068-2-20, IEC 60068-2-58, IEC 60068-2-69, IEC 60068-2-83, and to IEC 61760-1, which defines requirements to the specification of surface mounting components. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60068-2-20:2008, Environmental testing – Part 2: Tests – Test T: Test methods for solderability and resistance to soldering heat of devices with leads IEC 60068-2-58, Environmental testing – Part 2-58: Tests – Test Td: Test methods for solderability, resistance to dissolution of metallization and to soldering heat of surface mounting devices (SMD) IEC 60068-2-69, Environmental testing – Part 2-69: Tests – Test Te: Solderability testing of electronic components for surface mounting devices (SMD) by the wetting balance method1 IEC 60068-2-83, Environmental testing – Part 2-83: Tests – Test Tf: Solderability testing of electronic components for surface mounting devices (SMD) by the wetting balance method using solder paste IEC 61760-1, Surface mounting technology – Part 1: Standard method for the specification of surface mounting components (SMDs) IEC 62137-3, Electronics assembly technology – Part 3: Selection guidance of environmental and endurance test methods for solder joints 3 Terms, definitions and abbreviations 3.1 Terms and definitions For the purposes of this document the following terms and definitions apply. 3.1.1
solderability ability of the lead, termination or electrode of a component to be wetted by solder at the temperature of the termination or electrode, which is assumed to be the lowest temperature in the soldering process within the applicable temperature range of the solder alloy ________________ 1
A new edition (third edition) is currently under consideration. SIST EN 60068-3-13:2016
IEC 60068-3-13:2016 IEC 2016 – 7 – Note 1 to entry: The term “solderability” is often used in combination with the term “test”, indicating a specific method to evaluate the wettability or ability to be soldered of a surface under worst case conditions (soldering temperature and contact time with solder). It is not to be confused with the concepts “ability to be soldered” (see 4.1, 5.1.1) or “soldering ability” (see 3.1.4). 3.1.2
resistance to soldering heat ability of the component to withstand the highest temperature stress in terms of temperature gradient, peak temperature and duration of the soldering process, where the temperature of the component body is within the applicable temperature range of solder alloy 3.1.3
wettability intrinsic property of the termination material to form an alloy with the solder Note 1 to entry: Wettability depends on the base metal used to produce the termination or, in the case of a plated termination, the condition and material used to plate the base metal. 3.1.4
soldering ability ability of a specific combination of components to facilitate the formation of a proper solder joint Note 1 to entry: See 3.1.3, wettability. 3.2 Abbreviations SMD Surface mounted device SMT Surface mounting technology THD Through-hole mounting device THT Through-hole mounting technology THR Through-hole reflow soldering 4 Overview 4.1 Factors influencing the formation and reliability of solder joints (ability to be soldered) The conditions of ease of production and the reliability of a soldered joint can be classified in three groups, as follows. a) The joint design, determined by the choice of the two metallic elements to be joined (their shape, size, composition, etc.) and of the assembly method (relative position, initial fastening, etc.). b) The wettability of the surfaces to be joined. c) The conditions adopted for the soldering operation (temperature, time, flux, solder alloy, equipment, etc.). The choice of conditions of groups a) and c) concerns the manufacturer of equipment or subassemblies, who shall know the importance of each of the conditions and the limits of their variation. Condition b) depends to a large extent on the component manufacturer, except in cases of unusual handling or storage conditions by the equipment manufacturer. The wettability of surfaces needs to be defined with whatever degree of precision is necessary to allow the equipment manufacturer to choose conditions of classes a) and c) appropriate to that wettability. On the other hand, components of satisfactory surface quality will not necessarily prevent rejectable joints arising from faults in joint design or joining conditions. SIST EN 60068-3-13:2016
– 8 – IEC 60068-3-13:2016 IEC 2016 This often complex overlapping of responsibilities between component manufacturers and equipment manufacturers creates a need to be able to define with considerable precision the wettability of component terminations or, more generally, the solderability of components. 4.2 Physics of surface wetting In order to obtain wetting between a substrate and molten solder, the tin in the solder shall react with the substrate to form an alloy. In order to form an alloy the tin and the substrate has to come into molecular contact. In order to do this the surface of both the molten solder and the substrate shall be free from contamination. In order to better understand how molten solder spreads over a substrate, and what determines solderability, the surface tension property of the solder needs to be examined. A free droplet of molten solder held in free space will form into a globule shape, just as a free drop of water will form into a spherical shape. The droplet is held in this shape by the surface tension force of the molten solder. Inside the droplet the atoms are uniformly surrounded by other atoms, and the net force on them is zero, ignoring thermal motion. At the surface there is an imbalance in the inter-atomic attraction forces, as the surface atoms experience a net force into the body of the droplet. The complete system tries to adopt a shape that has the minimum free energy, which means the minimum surface-to-volume ratio. This situation is achieved when the molten solder forms into a sphere. The strength of the surface tension force is determined by the bond energies between the atoms within the molten solder. If the molten sphere of solder is placed onto a heated, oxidised copper plate, the shape of the sphere is depressed by gravity, to form a sessile drop, as shown in Figure 1 below.
Figure 1 – Sessile drop of solder on oxidised copper If a suitable flux is added to the sessile drop on the oxidised copper, the oxide layer will be removed from the copper and the solder, and the tin in the solder will react with the copper to form an intermetallic layer, allowing the solder to spread, as shown in Figure 2 below. IEC Solder Oxide layer SIST EN 60068-3-13:2016
IEC 60068-3-13:2016 IEC 2016 – 9 –
Figure 2 – Sessile drop of solder plus flux on clean copper The final shape of the spreading solder will depend on the surface tension forces acting at the interfaces. Solid and solid-liquid interfaces also exert a surface tension force, and all try to reduce their surface areas to a minimum to attain a minimum free energy. As a result equilibrium is reached whereby the net force at the advancing solder front is zero. Figure 3 below shows the forces acting at the advancing solder front. The surface tension of the solid copper in air is balanced by the surface tension between the liquid solder and the air, and the liquid solder and the solid copper.
Figure 3 – Sessile drop equilibrium forces The resulting forces at the advancing solder front can be written as follows: SA = LS + LA cos
where SA is surface tension between solid copper and air; LS is surface tension between liquid solder and solid copper; LA is surface tension between liquid solder and air. This equation is known as Young’s equation. The contact angle
can be used as a measure of the degree of spreading obtained. The smaller the contact angle, the greater the spreading, and the better the wetting obtained. If the cohesive forces within the solder are greater than the adhesive forces between the solder and the copper, then the solder will remain as a non-spreading sessile drop, and the contact angle will be greater than 90°. If the adhesive forces exceed the cohesive forces, then it is energetically favourable for the solder to react with the copper and spread outward, reducing the contact angle below 90°. IEC Solder Diffusion layer IEC γLA γLS γSA θ SIST EN 60068-3-13:2016
– 10 – IEC 60068-3-13:2016 IEC 2016 The surface tension between solid and air, SA, will be high when the solid is free from oxides, sulphides, chlorides, hydrocarbons and other surface contaminants, which will all reduce the surface tension. For the surface tension between liquid and solid, LS, to be low, a metallurgical bond has to be formed between the tin and the substrate. The surface tension between liquid solder and air, or flux film, will depend on the solder alloy, the soldering temperature and the flux used to solder the parts. The surface tension of the alloy can be markedly affected by the impurities in the solder. Very small levels of impurity can have a large effect on the surface tension. This is because the surface tension of a liquid is determined by the surface composition of the solder and not the composition of the bulk of the solder. Impurities with low surface energies will rapidly segregate to the surface of the liquid, reducing the surface tension, LA. Impurities in the solder alloy, and changes to the alloy composition may also affect the surface tension between the liquid and the solid, altering the intermetallic formation, and can also affect the surface tension between the solid and the air, affecting the diffusion process across the solid, ahead of the liquid front. Alloy additions or impurities may also affect the spreading and wetting properties of an alloy, by altering the viscosity of the liquid solder. 4.3 Quality and reliability of solder joints The quality of solder joints is characterised by wetted area, wetting angle, microstructure and specific visual criteria. One factor affecting the reliability of electronic assemblies is solder joint microstructure, which in turn depends on the thermal conditions under which the solder joint solidifies. Both the bulk microstructure of the solder and the intermetallic layer structure at the interfaces between solder and component termination should be taken into consideration. IEC 62137-3 gives guidance to test methods for the evaluation of solder joint reliability under consideration of the above described four elements. 5 Component soldering – Processes 5.1 General considerations 5.1.1 Components' ability to be soldered Because of the large variety of processing conditions a component can no longer simply be classified as suitable e.g. for “flow soldering” or “reflow soldering”, or “lead-free soldering”. Specific attention should be given to the fact, that the suitability of a component for “lead-free soldering” cannot be stated because of the variety of lead-free solder alloys and processing conditions. Typical soldering processes and related process conditions are described in IEC 61760-1. To be suitable for a certain soldering process a component shall fulfil the following requirements: a) material and surface of the component termination shall be suitable to be soldered with the solder alloy and soldering method; b) it shall possess thermal characteristics (thermal demand) small enough for a temperature sufficiently higher than the liquidus of the solder alloy used, to be reached and maintained for the length of time for wetting to occur; SIST EN 60068-3-13:2016
IEC 60068-3-13:2016 IEC 2016 – 11 – c) it shall withstand without short-term or long-term change the thermal stresses associated with the soldering cycle (including rework and possible repair by soldering iron); d) it shall withstand without short-term or long-term damage the mechanical and chemical stresses accompanying cleaning operations for the removal of flux residues. Cleaning considerations are not emphasized in this Guide. Thus, certain components containing lubricated mechanical parts (e.g. switches), or being unsealed are sensitive to contamination (e.g. relays, potentiometers), or containing plastic material with poor heat resistance (e.g. certain capacitors with thermoplastic dielectric), shall be carefully selected for mass-soldering operations because of their inability to withstand one or more of the stresses associated with the process. For these reasons careful distinction shall be made between the processability (ability to be soldered) of the component, which refers to the total suitability for industrial soldering, and the wettability of the termination, which refers only to the ease of coating the termination with solder. Unfortunately, these concepts are often confused in ordinary language, and such confusion can prevent smooth running of production. Furthermore, unsuitability of a component for soldering under the general conditions specified (see below) does not mean that its terminations cannot be soldered to a printed circuit board or other support. It entails only that it is necessary to take special precautions depending on the condition it does not satisfy, such as having thermally sensitive insulation, or incompatibility with some or all solvents. Only defective wettability of the terminations prevents the use of soldering for mounting the component. This quality is of prime importance, but does not exclude consideration of the others. The standardised tests referred to here are all directed to simulating some part of the effects of this set of conditions. The appropriate choice of a group of these tests, in conjunction with electrical and mechanical measurements, allows to answer the question: "ls this component solderable by the methods normally used in electronics?" This is one of the questions which the equipment manufacturer shall consider before putting a component on a soldering line. The principle of each standardised test and the degree of information it supplies are defined in Clause 7. In this way the component specifier can, in full knowledge of the reasons, select the number and type of tests needed to establish the behaviour of the component during soldering, as well as the requirements that shall be determined in every case to reflect the general requirements of the method of manufacture. Similarly, the person conducting the tests will appreciate the degree of information given.
– 12 – IEC 60068-3-13:2016 IEC 2016 5.1.2 Soldering processes Figure 4 shows typical soldering processes grouped into types.
Figure 4 – Typical soldering processes 5.1.3 Soldering defects The series IEC 61191 and IEC 61192 provide information about requirements for soldered electrical and electronic assemblies and related workmanship standards. • Non wetting, dewetting • Tombstoning • Shifting • Wicking • Bridging 5.1.4 Geometrical factors which may influence the soldering result • Land pattern design • Component geometry • Component terminal geometry • Insertion hole diameter • Annular ring 5.1.5 Process factors • Time – Temperature profile • Temperature spread (different temperatures at solder joints) • Atmosphere (air, nitrogen) 5.1.6 Material factors • Solder paste, solder alloy • Flux activity IEC Flow
soldering Reflow
soldering Special soldering
processes Wave (double, single) Selective (mini-wave, solder pot,
dip soldering) Convection (with or without IR support) Vapour phase Soldering iron Hot air Hot plate Induction / microwave soldering Laser Hot bar SIST EN 60068-3-13:2016
IEC 60068-3-13:2016 IEC 2016 – 13 – 5.2 Solder The composition of the solder alloy affects the surface tension of the liquid solder. Relatively small concentrations of impurities in the solder can have a marked effect on the wetting properties of the solder. Thus, the solder alloy used for soldering and for tests shall be described in the relevant specification. 5.3 Grouping of soldering conditions The melting temperatures of lead free solder alloys selected for industrial processes are significantly different from those of tin lead solder alloy. Moreover, the melting temperatures of present solder alloys are different from each other but can be clustered in groups. The ability of the SMD to withstand the typical temperature and dwell time conditions shall match the exposure to the process temperature groups using the selected alloys. The following groups of soldering processes in Table 1 are given as a guideline for selecting the severities for the wetting and resistance to soldering heat tests against the specified soldering heat profile. Table 1 – Solder process groups Process temperature group 1 Low 2 Medium 3 Medium-high 4 High Typical solder alloy family Sn-Bi Sn-Pb Sn-Ag-Cu Sn-Cu Flow – (235 to 250)°C (250 to 260)°C (250 to 260)°C Reflow (170 to 210)°C (210 to 240)°C (235 to 250)°C –
5.4 Ability to be soldered The ability to be soldered is determined mainly by the following three properties of a component. • Solderability of components The determination of solderability can be made at the time of manufacture, at receipt of the components by the user, or just before assembly and soldering. • Thermal demand It is necessary to bring the joint area to the soldering temperature. It is possible that the component design will allow the heat being applied to the joint area to be drained away into the component body, causing the temperature at the joint site to fall too low to produce an adequate solder joint. Preheat may be used to overcome thermal demand issues. • Resistance to soldering heat The component shall be able to withstand the thermal stress of the soldering process without any loss of functionality. This is particularly important with current assembly methods where components may experience rapidly changing thermal gradients. The result of this definition is that a matrix of soldering tests standards have evolved, which measure some or all of these three properties individually or in some cases a combination of the first two properties (see 7.2). 5.5 Moisture sensitivity of components The relevant specification may prescribe a moisture soak procedure to determine the sensitivity of a component against the influence of humidity during storage to the component body. SIST EN 60068-3-13:2016
– 14 – IEC 60068-3-13:2016 IEC 2016 NOTE 1 As distinguished from moisture soak the sensitivity of the component terminal surface against humidity is described by accelerated ageing (see 5.6.4). Typical soak conditions are: 85 °C/85 % r.h., 85 °C/60 % r.h., 60 °C/60 % r.h., 30 °C/60 % r.h. Duration of moisture soak (168 h to 696 h) depends on the diffusion speed of water and the absorption characteristics of the material. Thus, it needs specific investigation. NOTE 2 Examples for suitable soak procedures for semiconductor components may be found in IEC 60749-20 or J-STD-020. Applicable pre-drying and soak conditions for other types of components are under consideration. See also IEC 61760-4. 5.6 Relation between storage time/storage conditions and solderability 5.6.1 Natural and accelerated ageing Ageing is the natural process by which the solderability of a component decreases with time. The correlation between natural ageing and accelerated conditions (“accelerated ageing”) is difficult to be determined and cannot be generalized. The majority of component terminations are formed from a base material over which a solderable coating is applied to retain the solderability of the termination. It is common practice to plate a barrier layer over the base metal, before applying the solder coating, particularly if the base metal has a high solubility in solder. 5.6.2 Oxidation Tin forms an oxide SnO with the atmosphere, which forms a protective layer on the substrate. The rate of oxidation is accelerated by temperature and moisture in the atmosphere. Lead also forms an oxide PbO with the atmosphere, but generally SnO is formed preferentially as the tin has a greater affinity for oxygen. Sulphur levels in the atmosphere are generally low and tin and lead have very little reaction with sulphur at low concentration levels. Silver, however, reacts with sulphur at very low levels to form a black sulphide layer, which reduces the solderability of the substrate. Nitrous oxide (NO2) and chlorine both react with tin and lead to form lead nitrate (PbNO3) and tin and lead chlorides (SnCl2) (PbCl2). Lead nitrate forms a non-protective coating, which is difficult to solder. Both the chlorides are also non-protective and again reduce solderability (although the lead chloride is usually reduced to lead nitrate which cannot be soldered with normal electronic grade fluxes). 5.6.3 Growth of intermetallic layers The vast majority of electronic component terminations are coated with tin or tin-lead, and so most of the intermetallic layers contain tin. We have just seen that while the solder is molten the intermetallic layer is continually forming and being dissolved. In the solid state migration of the tin in the solder towards the intermetallic layer still continues, combined with diffusion of the substrate through the intermetallic, resulting in an increase in the thickness of the intermetallic layer into the solder coating. This process is proportional to the square root of the temperature and is significant even at room temperature. 5.6.4 Effect of ageing to wetting characteristics Typical ageing effects are: • degradation of metallic layers (oxidation); SIST EN 60068-3-13:2016
IEC 60068-3-13:2016 IEC 2016 – 15 – • degradation of organic constituents of galvanic platings; • growth of intermetallic phases through solderable surface; • cracking of the solderable surface. Degradation of wetting normally occurs in three distinct phases. a) Firstly the wetting time starts to increase as the solderability is reduced by the formation of oxides or corrosion products on the solder surface. b) Then there is a phase where no further deterioration occurs as the solder oxide layer protects the solder from further oxidation, by reducing the diffusion through the oxide layer and a chemical passivation of the surface. c) In the third phase the intermetallic layer has grown through to the surface of the solder coating, and the wetting time again begins to increase. Intermetallic growth is a major factor in the deterioration of the solderability of a solderable substrate, but the initial degradation is due to the reaction of the solderable coating with the atmosphere. 5.6.5 Test conditions for accelerated ageing The natural ageing process of a component is a very complicated process that would be impossible to accurately reproduce for each component, as we would need to be able to predict the storage environment and temperature over a long period. We therefore need to compress the ageing process into a much shorter time so that we can predict how components will age as they enter the factory. Clearly, it is impossible to produce an ageing method that will provide the same ageing mechanism as natural ageing. The international solderability specifications include a number of methods to accelerate the ageing process and provide data parallel to natural ageing, although the exact mechanism could never be the same. Typical ageing conditions are (see IEC 60068-2-20): • dry heat: at 155 °C for 2 h, 4 h, 16 h; • damp heat: at 40 °C, 93 % r.h. for 4 days, 10 days; • steam: in steam for 1 h, 4 h; • unsaturated pressurized vapour: at 125 °C, 85 % r.h. for 4 h. These methods either affect the surface of the solder by use of moisture or a corrosive atmosphere, or accelerate the rate of intermetallic growth by the use of high temperatures. Care has to be taken when using these methods as we have already seen that different pollutants in the atmosphere will produce different modifications to the solder surface. The aim of accelerated ageing methods is to compress one or two years of natural ageing into a few hours. We have seen that this is not possible as the mechanism of the ageing process changes as we increase the temperature to increase the reaction rates. Simulating the storage environment is also very difficult, in particular accelerating the effects of atmospheric pollutants, and predicting the pollutants that will be encountered, is almost impossible. In order to produce a similar mechanism to natural ageing it would be necessary to use a medium length process such as 40 °C, 93 % RH, which produces very similar effects to natural ageing on tin-lead. Different ageing processes will affect different plating materials, by different mechanisms. For example, dry heat at 155 °C will accelerate the intermetallic growth rate and oxide growth rate on a tin-lead coated component, but will have little effect on a silver-palladium component, which has already been fired at 800 °C during its manufacturing process. The solderability of a silver-palladium plated component will be affected by the levels SIST EN 60068-3-13
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...