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A Guide to Solder Paste - Precision Dispensing Systems ...

A Guide toSolder Paste 2 For many years, Nordson EFD has been formulating,manufacturing and supplying SolderPlus Solder pastes fordispense applications, SolderPlus Solder pastes for stencilprinting, and FluxPlus flux pastes to customers pastes are manufactured under highest quality standardsand provide outstanding batch-to-batch consistency toprovide our customers with high process EFD s SolderPlus Solder pastes are specificallyformulated for Dispensing application and provide unmatchedperformance. Combined with Nordson EFD dispensingsystems, they ensure a high yield application document provides an introduction to the fundamentalsof Solder Paste .

4 When choosing a solder alloy, there are four key considerations: lead content, melting temperature, alloy powder particle size and joint strength.

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Transcription of A Guide to Solder Paste - Precision Dispensing Systems ...

1 A Guide toSolder Paste 2 For many years, Nordson EFD has been formulating,manufacturing and supplying SolderPlus Solder pastes fordispense applications, SolderPlus Solder pastes for stencilprinting, and FluxPlus flux pastes to customers pastes are manufactured under highest quality standardsand provide outstanding batch-to-batch consistency toprovide our customers with high process EFD s SolderPlus Solder pastes are specificallyformulated for Dispensing application and provide unmatchedperformance. Combined with Nordson EFD dispensingsystems, they ensure a high yield application document provides an introduction to the fundamentalsof Solder Paste .

2 While there are many possible options whenformulating a Solder Paste , Nordson EFD s general purposesolder pastes will meet the requirements of most special requirements, Nordson EFD offers a wide range ofspecialized formulations. To find out which Solder Paste is thebest solution for your application, please contact yourNordson EFD Solder sales specialist for a free the Right Solder Paste34 When choosing a Solder alloy, there are four key considerations:lead content, melting temperature, alloy powder particle size andjoint strength. Lead content, melting temperature and strength are typicallyaddressed at the same time. The Alloy Chart (Figure 1) listsmelting and strength statistics, along with composition for 18typical Solder alloys.

3 At temperatures below the solidus, the alloy will be completelysolid. At temperatures above the liquidus, the alloy will becompletely liquid. In between, the alloy is in a plastic state andneither fully liquid nor fully solid, and strength is near zero. Forbest wetting, a peak temperature 15 C or more above liquidus isrequired. If a Solder joint needs to retain physical integrity duringa later operation, such as a second reflow process, the peaktemperature of the later operation needs to be below the solidustemperature of the first alloy. The Solder alloy tensile strength values listed are valid at 25 Cat a particular strain rate for a particular age of the alloy strength drops as temperature increases.

4 Near thesolidus, tensile strength approaches zero. When using strength values to make a decision, consider thevalues as a useful comparison to determine if one alloy is likelyto be better than another. Include a factor of two or more as asafety margin for joint variability, and to compensate for anyinaccuracy in the tensile strength value reported. Be mindfulthat alloys with higher solidus retain more strength at highertemperatures. Example: At 210 C Sn95 Ag5, which has asolidus of 221 C, is weaker than Sn5 Pb95, which has a solidusof 308 C, despite the higher tensile strength of Sn95 Ag5 at 25 picked an alloy, the required particle size is the next itemto identify.

5 The Powder Size Chart (Figure 2) cross-referencesparticle size to typical printing and Dispensing requirements. Thedimensions listed for gullwing, square/circle and dispense dotsizes represent the smallest feature recommended for that sizepowder. If the feature is smaller, the application requires the nextsmaller powder size. Using too large a powder will cause printing and dispensingdifficulties, compromising quality. Using a smaller powder willjust cost Alloy SelectionThe alloy requirements must be evaluated and an alloy identified as meeting all product requirements. 5 Figure 1 Figure 2 Lead-freeAlloy:Solidus ( C)Liquidus ( C)TensileStrength (psi)Sn42 Bi57 Sb52322405900Sn89 Sb10250257n/aAlloy ChartAlloy:Solidus ( C)Liquidus ( C)TensileStrength (psi)Sn43 Pb43 Bi141441636120Sn62 Pb36 Ag21791896700Sn63 Pb371836700Sn60 Pb401831916200Sn10 Pb88 Ag22682904900Sn10 Pb902753024600Sn5 Pb953083124190 Powder Size ChartPowder TypePowder Size (micron)Gullwing Lead Pitch (mm)Square/Circle Aperture (mm)/(in)Dispense Dot Dia.

6 (mm)/(in)II45-75 / / / / / / / / / / / / / / / specifications and industry usage have contributed tocurrent naming conventions for fluxes. Industry conventionincludes five basic categories of fluxes to choose from: R, RMA,RA, NC and WS. The following summary is an explanation ofhow specifications affected the categories. There are four categories of flux to choose from, as defined byMilitary Specification QQ-S-571E: Rosin (R) Rosin or Resin Mildly Activated (RMA) Rosin or Resin Activated (RA) Non-rosin or non-resin, commonly refered to in the industryas Water Soluble (WS). Each category of flux is available with a variety of activity levels,with the limits of each defined by applicable test results.

7 IPC also has a flux rating system. The system uses fourcharacters to describe any flux as published in four characters describe the product in terms of materialtype, including but not limited to such categories as rosin andinorganic, along with an approximation of activity level and halidecontent. Example: a halide-free, rosin-based Solder Paste withlow activity is categorized as ROL0. RO stands for rosin, the L isfor low activity and the number 0 is for no detectable halides. Flux type: RO: Rosin OR: Water soluble Activity level: Low: L Medium: M High: HHalides detectable No: 0 Yes: 1In addition, the IPC standard added a category of flux calledNo Clean (NC).

8 This new category of flux is defined by non-tacky residue and compliance with a Surface InsulationResistance (SIR) test to a value of 1x108 . Each of the five flux categories can be described in brief bynoting their activity, the physical qualities of their residue andthe cleaning methods that may be used in their removal. Rosin (R)flux consists of rosin and solvent. Rosin flux has verylow activity and is suitable only for clean and easy-to-soldersurfaces. IPC classification is usually ROL0. R residue is hard,non-corrosive, non-conductive, and may be left on many typesof assemblies. Residue may be removed with an Clean (NC)flux consists of rosin, solvent and a small amountof activator.

9 NC flux typically has low-to-moderate activity andis suited to easily solderable surfaces. IPC classification is2. Flux Type SelectionThe flux types that are valid options must be identified. This is a process of elimination, where fluxeswith unacceptable criteria are removed from ROL0 or ROL1. NC residue is clear, hard, non-corrosive,non-conductive, and designed to be left on many types ofassemblies. Residue may be removed with an appropriatesolvent. Some, but not all, NC fluxes are more difficult toremove than RMA fluxes. Rosin mildly activated (RMA)flux consists of rosin, solventand a small amount of activator. Most RMA flux is fairly low inactivity and best suited to easily solderable surfaces.

10 IPCclassification is usually ROL0, ROL1, ROM0 or ROM1. RMA fluxresidue is clear and soft. Most are non-corrosive andnonconductive. Cleaning requirements will be based on theactivity of the flux and the product it is used on. Many RMAfluxes pass SIR testing as a NC flux. Residue may be removedwith an appropriate solvent. Rosin activated (RA)flux consists of rosin, solvent andaggressive activators. RA flux has similar and higher activitythan RMA for moderately and highly oxidized surfaces. IPCclassification is usually ROM0, ROM1, ROH0 or ROH1. RAflux residue is considered corrosive. Assemblies sensitive tocorrosion or the possibility of electrical conduction through theresidue should be cleaned as soon as possible after may be removed with an appropriate solvent.


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