[{"data":1,"prerenderedAt":64},["ShallowReactive",2],{"blog-solder-non-wetting-vs-dewetting-en":3},{"title":4,"description":5,"date":6,"lastUpdated":6,"category":7,"image":8,"readingTime":9,"wordCount":10,"timeRequired":11,"htmlContent":12,"faq":13,"tags":29,"slug":33,"sourceLocale":34,"availableLocales":35,"jsonld":40},"Solder Non-Wetting vs Dewetting: How to Diagnose Both","Distinguish solder non-wetting from dewetting using joint patterns, material history and process evidence, while recognizing the limits of visual inspection.","2026-10-31","assembly",null,12,2312,"PT12M","\u003Cp>\u003Cstrong>Non-wetting means solder fails to adhere to all or part of a surface it contacts. Dewetting means solder first spreads over a surface and then recedes.\u003C/strong> Both can leave an irregular-looking joint, but they describe different process histories—and a photograph taken after soldering usually cannot establish that history by itself.\u003C/p>\n\u003Cp>Start by identifying \u003Cem>where\u003C/em> the solder is absent, what material should have been solderable there, and whether the joint received enough heat, solder and active flux. Then compare the affected locations with unaffected joints and retained materials before choosing a test or rework method. A visual symptom is a reason to investigate, not automatically a verdict on the board finish, component or assembly process.\u003C/p>\n\u003Cp>This article focuses on interpreting patterns on assembled joints. For test methods and acceptance planning, see \u003Ca href=\"/en/blog/pcb-solderability-testing/\">PCB solderability testing\u003C/a>. For incomplete melting, profiles and related process defects, see \u003Ca href=\"/en/blog/reflow-soldering/\">reflow soldering\u003C/a>.\u003C/p>\n\u003Ch2>What wetting means at a solder joint\u003C/h2>\n\u003Cp>Wetting occurs when molten solder contacts a suitable surface, spreads and forms an interface with it. In a sound joint, that interface must develop appropriately over the required portions of the pad and termination. The result depends on both the materials and the process: surface condition, flux action, temperature, exposure time and solder availability all matter.\u003C/p>\n\u003Cp>A useful observation is not merely “the solder looks dull” or “the metal is visible.” Record which specific surface is involved:\u003C/p>\n\u003Cul>\n\u003Cli>The PCB pad or plated through-hole barrel\u003C/li>\n\u003Cli>The component lead or termination\u003C/li>\n\u003Cli>A region close to the solder mask\u003C/li>\n\u003Cli>A location where solder was never intended to cover the surface\u003C/li>\n\u003C/ul>\n\u003Cp>The exposed appearance of a pad finish, a component termination and the solder alloy can be difficult to distinguish in an image. Lighting, residue and viewing angle can also obscure the boundary. Identify the materials and the intended solderable area before interpreting the pattern.\u003C/p>\n\u003Ch2>Non-wetting: failure to adhere to a contacted surface\u003C/h2>\n\u003Cp>Non-wetting is a failure of solder to adhere to an initially contacted surface, either across the relevant area or locally. The solder may appear to have pulled into a mass alongside a region it did not adhere to, or coverage may be incomplete on one side of a joint.\u003C/p>\n\u003Cp>Possible contributors include:\u003C/p>\n\u003Cul>\n\u003Cli>Oxidation or contamination on the pad or termination\u003C/li>\n\u003Cli>An unsuitable or degraded solderable surface\u003C/li>\n\u003Cli>Insufficient flux delivery or flux activity at the affected location\u003C/li>\n\u003Cli>Process exposure that leaves the surface poorly protected before solder contact\u003C/li>\n\u003Cli>Local thermal conditions that prevent the intended soldering action\u003C/li>\n\u003C/ul>\n\u003Cp>Those are hypotheses, not conclusions drawn from appearance alone. For example, a pad-side pattern repeated across different component types suggests a different investigation from a pattern confined to one component termination lot. Neither pattern proves the cause.\u003C/p>\n\u003Ch2>Dewetting: solder spreads and then recedes\u003C/h2>\n\u003Cp>Dewetting describes a sequence: solder initially spreads, then withdraws from part of the wetted area. Investigating it therefore requires evidence about process history, not just the final shape.\u003C/p>\n\u003Cp>The \u003Cstrong>ALPHA Wave Soldering Troubleshooting Guide\u003C/strong> describes non-wetting in its wave-process context as leaving exposed basis metal, while its dewetting description includes a thin solder film with the basis metal not exposed. ZVEI’s \u003Cstrong>Guidelines for Long-Term Storage\u003C/strong>, section 4.7, also discusses solder receding from initially wetted areas and nonsolderable areas.\u003C/p>\n\u003Cp>These descriptions are useful, but they are not universal visual pass/fail rules. Terminology, thin-film interpretation, exposed-metal treatment and acceptance depend on the specified standard, revision and test or inspection method. A finished joint that appears to contain a thin film does not, by itself, prove solder spread and receded; nor does visible metal automatically establish non-wetting.\u003C/p>\n\u003Cp>Stronger evidence may come from a documented in-process observation or a suitably designed comparison under known conditions. Even then, relate the result to the product and process being investigated rather than assuming it describes every joint in the lot.\u003C/p>\n\u003Ch2>Separate wetting symptoms from other joint defects\u003C/h2>\n\u003Cp>A joint can have inadequate coverage without the initial cause being a surface-wetting failure. Check these alternatives before assigning a wetting label:\u003C/p>\n\u003Cul>\n\u003Cli>\u003Cstrong>Insufficient melting or local heat:\u003C/strong> Paste or solder may not have reached the required molten condition at a particular joint. Compare the actual thermal exposure at that location with nearby joints and the process requirements. A cold-joint appearance is a symptom, not a complete root-cause diagnosis.\u003C/li>\n\u003Cli>\u003Cstrong>Insufficient solder volume:\u003C/strong> A poor paste deposit, missing preform or inadequate solder supply can leave a small joint even where the available solder wetted normally. Review deposit records and the joint design as well as the finished appearance.\u003C/li>\n\u003Cli>\u003Cstrong>Excessive or uneven process exposure:\u003C/strong> Heat and time can affect surfaces and flux before the solder contacts the joint. This is distinct from simply saying the joint was “too cold.”\u003C/li>\n\u003Cli>\u003Cstrong>Design or geometry effects:\u003C/strong> Pad geometry, termination shape, solder-mask registration and local thermal mass can change how solder is delivered and where it is expected to spread.\u003C/li>\n\u003C/ul>\n\u003Cp>Do not use contact angle, color, shininess or visible metal as a universal acceptance test. Apply the product’s agreed workmanship criteria and revision to the actual joint type. The \u003Ca href=\"/en/blog/solder-paste/\">solder paste guide\u003C/a> provides useful context when the deposit and paste condition are part of the investigation.\u003C/p>\n\u003Ch2>A practical decision table\u003C/h2>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth>Observation or evidence\u003C/th>\n\u003Cth>What it can suggest\u003C/th>\n\u003Cth>Next check—not an automatic conclusion\u003C/th>\n\u003C/tr>\n\u003C/thead>\n\u003Ctbody>\u003Ctr>\n\u003Ctd>Coverage is incomplete mainly on PCB pads across several component types\u003C/td>\n\u003Ctd>A common board surface, local process exposure or flux-delivery issue\u003C/td>\n\u003Ctd>Map affected pads by board lot and position; inspect retained boards and compare process records\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>Coverage is incomplete mainly on one component’s terminations across boards\u003C/td>\n\u003Ctd>A termination-specific material or handling issue, or a geometry-related process issue\u003C/td>\n\u003Ctd>Trace component lots and storage history; compare the same location and component type using retained material where available\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>Several locations show poor coverage after a documented flux or process change\u003C/td>\n\u003Ctd>Flux delivery, activation or exposure deserves review\u003C/td>\n\u003Ctd>Compare actual settings, materials and recorded conditions; confirm whether other variables also changed\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>Paste remains visibly uncoalesced or a local joint shows evidence of inadequate melting\u003C/td>\n\u003Ctd>Local heat transfer or profile exposure may be insufficient\u003C/td>\n\u003Ctd>Review a representative thermal profile and sensor locations; compare the suspect joint with neighboring joints\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>A joint is small, but the available solder appears to have adhered\u003C/td>\n\u003Ctd>Solder supply or deposition may be insufficient\u003C/td>\n\u003Ctd>Review paste deposit, placement, pad design and relevant inspection records\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>Solder was observed spreading and then withdrawing under documented conditions\u003C/td>\n\u003Ctd>Dewetting is a credible description of that observed sequence\u003C/td>\n\u003Ctd>Identify the surface, flux, temperature and timing; compare with the applicable specification\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>Only a post-process image is available\u003C/td>\n\u003Ctd>The image establishes an appearance, not necessarily the wetting sequence\u003C/td>\n\u003Ctd>Preserve the assembly and gather material and process history before assigning cause\u003C/td>\n\u003C/tr>\n\u003C/tbody>\u003C/table>\n\u003Cp>The table directs the next investigation; it does not replace acceptance criteria. A joint can involve more than one contributor—for example, a marginal surface combined with local process conditions.\u003C/p>\n\u003Ch2>Investigate in a sequence that preserves evidence\u003C/h2>\n\u003Ch3>1. Hold and document before rework\u003C/h3>\n\u003Cp>Place suspect material under the project’s hold process and record its identifiers and quantity. Photograph representative joints at useful magnification, including both affected and unaffected examples. Capture board orientation, component reference, pad or lead location, lot identifiers and the solder-mask condition around the joint.\u003C/p>\n\u003Cp>Retain representative assembled units, unused boards, components and relevant material samples where available. Do not strip solder mask or otherwise alter a sample simply to make the initial inspection easier; its condition and position may be relevant.\u003C/p>\n\u003Cp>Cleaning, baking or another reflow cycle can change the evidence. Do not apply any of them as a blanket first response. Decide whether they are appropriate only after the affected parties have reviewed the failure, material limits and proposed investigation or rework plan.\u003C/p>\n\u003Ch3>2. Map the distribution\u003C/h3>\n\u003Cp>Create a joint-level record rather than counting only failed boards. Note whether the pattern follows:\u003C/p>\n\u003Cul>\n\u003Cli>A board lot, panel location or pad type\u003C/li>\n\u003Cli>A component type, termination style or component lot\u003C/li>\n\u003Cli>A particular side of a component or position on the assembly\u003C/li>\n\u003Cli>A production shift, material change or process interval\u003C/li>\n\u003Cli>A specific flux, paste or soldering operation\u003C/li>\n\u003C/ul>\n\u003Cp>Also record what looks normal. A good comparison needs comparable joint designs, inspection conditions and acceptance definitions. If every suspect joint is in one region of the board, local thermal mass or process access may be as important to investigate as the incoming materials.\u003C/p>\n\u003Ch3>3. Review the available history\u003C/h3>\n\u003Cp>Collect the records that can distinguish material condition from process exposure: board finish and lot, component termination and lot, storage and handling history, paste or flux identification, and relevant process records. Where a reflow profile is used as evidence, check that its measured locations represent the suspect area and that the run is relevant to the assembly being investigated.\u003C/p>\n\u003Cp>For wave soldering, review the actual flux application and process sequence as well as solder contact conditions. For reflow, examine paste deposition and local heating alongside the finish and termination condition. The same final appearance can arise from different combinations of variables.\u003C/p>\n\u003Cp>The \u003Ca href=\"/en/blog/pcb-surface-finish-comparison/\">PCB surface finish comparison\u003C/a> can help frame finish selection, but a finish name alone cannot establish the condition of a particular delivered lot.\u003C/p>\n\u003Ch3>4. Compare and test deliberately\u003C/h3>\n\u003Cp>Select tests to answer a stated question. Examples include comparing retained board material or component leads under an agreed solderability method, inspecting paste deposits, reviewing a representative thermal profile, or examining a selected joint cross-section.\u003C/p>\n\u003Cp>A solderability test on retained material can help assess that sample under the specified method. It does not automatically reproduce the original assembly operation. A cross-section can reveal features of a finished joint, but it generally cannot establish by itself whether solder first spread and then receded. Destructive examination also consumes evidence, so agree on sample selection and authorization first.\u003C/p>\n\u003Cp>Electrical continuity alone is not a substitute for the agreed visual and workmanship assessment. Likewise, choose imaging or other inspection tools for the question they can answer, rather than assuming a single method can identify the cause. See \u003Ca href=\"/en/blog/pcb-inspection/\">PCB inspection\u003C/a> for related inspection considerations.\u003C/p>\n\u003Ch2>How to interpret a small comparison\u003C/h2>\n\u003Cp>Suppose an inspection finds \u003Cstrong>12 suspect joints in 24 from lot A\u003C/strong> and \u003Cstrong>2 suspect joints in 24 from lot B\u003C/strong>:\u003C/p>\n\u003Cul>\n\u003Cli>Lot A: 12 ÷ 24 = 0.50 = \u003Cstrong>50%\u003C/strong>\u003C/li>\n\u003Cli>Lot B: 2 ÷ 24 = 0.0833… = \u003Cstrong>8.3%\u003C/strong>, rounded to one decimal place\u003C/li>\n\u003C/ul>\n\u003Cp>Both groups contain the same number of inspected joints, which makes the observed proportions straightforward to compare. The counts do \u003Cstrong>not\u003C/strong> establish that lot A caused the defects.\u003C/p>\n\u003Cp>For the comparison to guide the investigation, record the joint types, boards sampled, inspection criteria and production conditions. Joints on the same assembly may share materials and process exposure; they are not necessarily independent samples. If the lots were assembled at different times or with different components, profiles or operators, those differences can also matter. This is an observation to investigate, not a controlled experiment.\u003C/p>\n\u003Ch2>Assign responsibilities and release criteria\u003C/h2>\n\u003Cp>An effective investigation identifies who owns each record and decision without assuming a particular party caused the issue.\u003C/p>\n\u003Cul>\n\u003Cli>\u003Cstrong>The product owner or engineering team\u003C/strong> identifies the affected function, approved design, applicable acceptance standard and revision, and disposition authority.\u003C/li>\n\u003Cli>\u003Cstrong>The assembler\u003C/strong> provides the assembly and process records available for the affected build, identifies retained material where available, and participates in an agreed investigation or rework plan.\u003C/li>\n\u003Cli>\u003Cstrong>Board and component suppliers\u003C/strong> provide relevant material identification and available manufacturing or handling information for the supplied lots.\u003C/li>\n\u003Cli>\u003Cstrong>The parties together\u003C/strong> agree on sample selection, any external testing, interpretation of results, corrective action and release.\u003C/li>\n\u003C/ul>\n\u003Cp>Before releasing material or requesting a new build, put the following fields in the record or RFQ:\u003C/p>\n\u003Col>\n\u003Cli>Assembly part number and revision; affected board, component and material lot identifiers\u003C/li>\n\u003Cli>Joint locations, quantities inspected and suspect counts, with representative photographs\u003C/li>\n\u003Cli>Required acceptance standard, revision, joint class or other applicable product criteria\u003C/li>\n\u003Cli>Board finish and component termination requirements, including any agreed storage and handling controls\u003C/li>\n\u003Cli>Solder alloy, paste or flux requirements, and the applicable soldering process\u003C/li>\n\u003Cli>Available process history and the specific question each proposed test must answer\u003C/li>\n\u003Cli>Sample ownership, destructive-test authorization, rework limits and disposition authority\u003C/li>\n\u003Cli>Required evidence for closure and who must approve release\u003C/li>\n\u003C/ol>\n\u003Cp>For a new assembly request, include the design files and applicable manufacturing information as well as any known wetting concerns. HILPCB’s \u003Ca href=\"/en/products/smt-assembly/\">SMT assembly service\u003C/a> may be relevant to the project; specific investigation, inspection, testing and rework responsibilities should be established in the project agreement. Use the \u003Ca href=\"/en/quote/\">quote request\u003C/a> to share build requirements or \u003Ca href=\"/en/contact/\">contact HILPCB\u003C/a> to discuss the evidence and intended scope.\u003C/p>\n\u003Cdiv data-component=\"BlogQuickQuoteInline\">\u003C/div>\n\u003C!-- faq:start -->\n\u003Ch2>FAQs\u003C/h2>\n\u003Ch3>Can a photograph distinguish non-wetting from dewetting?\u003C/h3>\n\u003Cp>It can show the final coverage pattern, but usually not whether solder first spread and receded. Use process observations and other evidence to investigate the sequence.\u003C/p>\n\u003Ch3>Does exposed metal always mean a joint fails?\u003C/h3>\n\u003Cp>No. Identify the exposed material and intended solderable area, then apply the specified acceptance criteria for that joint and product. Appearance alone is not a universal rule.\u003C/p>\n\u003Ch3>Is a cold joint the same as non-wetting?\u003C/h3>\n\u003Cp>No. A cold-joint appearance can be associated with inadequate melting or heat, among other conditions. Non-wetting describes failure to adhere to a contacted surface; the investigation should consider both possibilities.\u003C/p>\n\u003Ch3>Should suspect assemblies be cleaned and reflowed immediately?\u003C/h3>\n\u003Cp>Not as a blanket response. Cleaning or reheating can alter evidence and may affect the assembly. Hold samples and agree on an investigation and rework plan first.\u003C/p>\n\u003Ch3>Will a solderability test prove what happened in assembly?\u003C/h3>\n\u003Cp>Not necessarily. It evaluates selected material under a specified method. Compare its conditions and sample history with the original build before drawing conclusions.\u003C/p>\n\u003C!-- faq:end -->\n\u003Csection class=\"related-links\" aria-label=\"Related\">\u003Ch3>Related links\u003C/h3>\u003Cul>\u003Cli>\u003Ca href=\"/en/blog/pcb-solderability-testing/\">PCB Solderability Testing for Reliable Electronic Assembly\u003C/a>\u003C/li>\u003Cli>\u003Ca href=\"/en/blog/reflow-soldering/\">Reflow Soldering: Process Stages, Temperatures and Reflow vs Wave Soldering\u003C/a>\u003C/li>\u003Cli>\u003Ca href=\"/en/blog/solder-paste/\">What Is Solder Paste? Composition, Alloys, Storage and How It Is Used in SMT\u003C/a>\u003C/li>\u003Cli>\u003Ca href=\"/en/blog/pcb-surface-finish-comparison/\">PCB Surface Finish Comparison: HASL, OSP, ENIG, Immersion Silver, and Immersion Tin in Mass Production\u003C/a>\u003C/li>\u003Cli>\u003Ca href=\"/en/blog/pcb-inspection/\">PCB Inspection Services: AOI, X-Ray, and Quality Control Solutions\u003C/a>\u003C/li>\u003Cli>\u003Ca href=\"/en/products/smt-assembly/\">SMT assembly service\u003C/a>\u003C/li>\u003Cli>\u003Ca href=\"/en/quote/\">quote request\u003C/a>\u003C/li>\u003C/ul>\u003C/section>",[14,17,20,23,26],{"question":15,"answer":16,"answerText":16},"Can a photograph distinguish non-wetting from dewetting?","It can show the final coverage pattern, but usually not whether solder first spread and receded. Use process observations and other evidence to investigate the sequence.",{"question":18,"answer":19,"answerText":19},"Does exposed metal always mean a joint fails?","No. Identify the exposed material and intended solderable area, then apply the specified acceptance criteria for that joint and product. Appearance alone is not a universal rule.",{"question":21,"answer":22,"answerText":22},"Is a cold joint the same as non-wetting?","No. A cold-joint appearance can be associated with inadequate melting or heat, among other conditions. Non-wetting describes failure to adhere to a contacted surface; the investigation should consider both possibilities.",{"question":24,"answer":25,"answerText":25},"Should suspect assemblies be cleaned and reflowed immediately?","Not as a blanket response. Cleaning or reheating can alter evidence and may affect the assembly. Hold samples and agree on an investigation and rework plan first.",{"question":27,"answer":28,"answerText":28},"Will a solderability test prove what happened in assembly?","Not necessarily. It evaluates selected material under a specified method. Compare its conditions and sample history with the original build before drawing conclusions.",[30,31,32],"solder non-wetting","solder dewetting","PCB solderability","solder-non-wetting-vs-dewetting","en",[34,36,37,38,39],"de","cn","fr","ru",{"blog":41,"breadcrumb":50},{"@context":42,"@type":43,"headline":4,"description":5,"url":44,"datePublished":6,"dateModified":6,"timeRequired":11,"keywords":45,"articleSection":7,"author":46,"publisher":49},"https://schema.org","BlogPosting","https://hilpcb.com/en/blog/solder-non-wetting-vs-dewetting/","solder non-wetting, solder dewetting, PCB solderability",{"@type":47,"name":48},"Organization","HILPCB",{"@type":47,"name":48},{"@context":42,"@type":51,"itemListElement":52},"BreadcrumbList",[53,58,62],{"@type":54,"position":55,"name":56,"item":57},"ListItem",1,"Home","https://hilpcb.com/",{"@type":54,"position":59,"name":60,"item":61},2,"Blog","https://hilpcb.com/en/blog/",{"@type":54,"position":63,"name":33,"item":44},3,1794062105032]