{"id":1519,"date":"2026-10-21T15:00:00","date_gmt":"2026-10-21T07:00:00","guid":{"rendered":"https:\/\/www.jingpengpcb.com\/?p=1519"},"modified":"2026-10-08T20:15:03","modified_gmt":"2026-10-08T12:15:03","slug":"smt-advantages-pad-wetting-issues","status":"publish","type":"post","link":"https:\/\/www.jingpengpcb.com\/en\/blog\/smt-advantages-pad-wetting-issues\/","title":{"rendered":"What Are the Advantages of SMT Technology? An Analysis of Reliability, Density, and High-Frequency Characteristics"},"content":{"rendered":"<style>\n.jp-tw{overflow-x:auto;margin:26px 0;-webkit-overflow-scrolling:touch;}\n.jp-tw table{border-collapse:collapse;width:100%;min-width:560px;font-size:15px;line-height:1.65;background:#fff;}\n.jp-tw th,.jp-tw td{border:1px solid #dde3ea;padding:11px 14px;text-align:left;vertical-align:top;}\n.jp-tw thead th{background:#eef2f7;color:#1b2733;font-weight:700;white-space:nowrap;border-bottom:2px solid #c9d3de;}\n.jp-tw tbody tr:nth-child(even){background:#fafbfc;}\n.jp-tw tbody tr:hover{background:#f1f5fa;}\n.jp-tw tbody td:first-child{font-weight:600;color:#1b2733;}\n@media(max-width:767px){.jp-tw table{font-size:14px;min-width:520px;}.jp-tw th,.jp-tw td{padding:9px 11px;}}\n<\/style>\n<p>In the field of modern electronics manufacturing, SMT (Surface Mount Technology) has become the mainstream method. At the same time, poor wetting of PCB pads is a common issue. This article will explore the advantages of SMT technology and provide an analysis of poor PCB pad wetting, helping you better understand these two topics closely related to electronics manufacturing.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"1512\" height=\"851\" class=\"alignnone size-large wp-image-8901\" src=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/12-suggestions-for-smt-processing-and-welding.jpg\" alt=\"12 Tips for SMT Soldering\" srcset=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/12-suggestions-for-smt-processing-and-welding.jpg 1512w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/12-suggestions-for-smt-processing-and-welding-300x169.jpg 300w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/12-suggestions-for-smt-processing-and-welding-1024x576.jpg 1024w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/12-suggestions-for-smt-processing-and-welding-768x432.jpg 768w\" sizes=\"auto, (max-width: 1512px) 100vw, 1512px\" \/><\/p>\n<h2>SMT Wafer Processing Technology<\/h2>\n<p><a href=\"\/en\/smt-factory\/\">SMT Assembly<\/a>Surface-mount technology (SMT) has come to play a vital role in electronics manufacturing. By mounting components directly onto the surface of a PCB rather than using through-hole assembly, it offers numerous advantages for electronic products. Below, we will detail several key advantages of SMT technology.<\/p>\n<h3>1. High reliability and strong vibration resistance<\/h3>\n<p>SMT assembly uses highly reliable surface-mount components, which are small, lightweight, and highly vibration-resistant. These components are typically manufactured using automated processes, resulting in a high level of assembly reliability. In SMT assembly, the defect rate for solder joints is typically less than 0.01%, which means the reliability of electronic products is well assured. In fact, nearly 90% of electronic products utilize SMT technology.<\/p>\n<h3>2. Electronic products are compact and have high assembly density.<\/h3>\n<p>SMT modules are only about one-tenth the size of traditional components and weigh just 10% of traditional components. Through surface-mount technology, the volume of electronic products can be reduced by 40% to 60%, and their performance can be improved by 60% to 80%, while their footprint and weight are also significantly reduced.<\/p>\n<p>SMT assembly has also enabled the component pitch to shrink from 1.27 mm to 0.63 mm, with some pitches now as small as 0.5 mm. Using through-hole mounting technology to install components allows for higher assembly density.<\/p>\n<h3>3. High-frequency performance and reliable operation<\/h3>\n<p>SMT assembly offers exceptional high-frequency performance. Because chip modules are securely mounted and components typically feature leadless or short leads, the effects of parasitic inductance and capacitance are reduced, which improves the circuit\u2019s high-frequency performance and minimizes electromagnetic and radio-frequency interference. Circuits designed using SMC and SMD technologies can operate at frequencies as high as 3 GHz, whereas surface-mount modules are limited to 500 MHz, thereby reducing signal propagation delay. These characteristics make SMT technology suitable for circuits with clock frequencies higher than 16 MHz; through MCM technology, high-end computer workstations can even achieve clock frequencies of up to 100 MHz, thereby reducing additional power consumption.<\/p>\n<h2>Advanced: What Processes Make Up an SMT Production Line?<\/h2>\n<p>The advantages of SMT are only realized on the production line. A typical SMT production line consists of the following processes in sequence; if any one of them goes awry, it will directly result in defective solder joints:<\/p>\n<ol>\n<li><strong>Solder Paste Printing<\/strong>: Align the steel mesh with the pads, then use the squeegee to spread the solder paste across the openings, depositing a measured amount of solder paste on each pad;<\/li>\n<li><strong>Mounting<\/strong>: The pick-and-place machine picks up components based on the coordinate file and places them in the corresponding positions;<\/li>\n<li><strong>Reflow Soldering<\/strong>: Melt the solder paste according to the preset temperature profile to form solder joints;<\/li>\n<li><strong>Testing<\/strong>: AOI (automatic optical inspection); X-ray inspection for hidden solder joints in BGAs, etc.; electrical testing as needed;<\/li>\n<li><strong>Repair and Panel Separation<\/strong>: Repair defective areas by spot welding or replace them, and finally separate the boards according to the panel layout.<\/li>\n<\/ol>\n<p>Compared with traditional through-hole technology (THT), the differences between the two can be summarized as follows:<\/p>\n<div class=\"jp-tw\">\n<table>\n<thead>\n<tr>\n<th>Comparison Items<\/th>\n<th>SMT<\/th>\n<th>THT<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Assembly Density<\/td>\n<td>Tall, can be mounted on either side<\/td>\n<td>Low; a jack must be provided<\/td>\n<\/tr>\n<tr>\n<td>Device Dimensions<\/td>\n<td>Small; the smallest size available is 01005<\/td>\n<td>Large; requires a hole for the pin<\/td>\n<\/tr>\n<tr>\n<td>High-Frequency Characteristics<\/td>\n<td>Parasitic parameter is small<\/td>\n<td>Long leads result in large parasitic components<\/td>\n<\/tr>\n<tr>\n<td>Vibration Resistance<\/td>\n<td>Okay, the device is lightweight and flush with the surface.<\/td>\n<td>It's fairly heavy and rests on its legs.<\/td>\n<\/tr>\n<tr>\n<td>Level of Automation<\/td>\n<td>Fully Automated<\/td>\n<td>Requires a plugin; automation is limited<\/td>\n<\/tr>\n<tr>\n<td>Difficulty of Repair<\/td>\n<td>Special tools are required<\/td>\n<td>Relatively easy<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"1430\" height=\"805\" class=\"alignnone size-large wp-image-8449\" src=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/pcba-smt-processing-control-and-management.jpg\" alt=\"Control and Management of PCBA Surface-Mount Assembly\" srcset=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/pcba-smt-processing-control-and-management.jpg 1430w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/pcba-smt-processing-control-and-management-300x169.jpg 300w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/pcba-smt-processing-control-and-management-1024x576.jpg 1024w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/pcba-smt-processing-control-and-management-768x432.jpg 768w\" sizes=\"auto, (max-width: 1430px) 100vw, 1430px\" \/><\/p>\n<p>For key management points on the production line, please refer to<a href=\"\/en\/blog\/pcba-smt-processing-control-and-management\/\">Control and Management of PCBA Surface-Mount Assembly<\/a>, The operating procedures for the placement machine itself are as follows:<a href=\"\/en\/faq\/operation-process-of-smt-machine\/\">SMT Placement Machine Operating Procedures<\/a>An article.<\/p>\n<h2>Analysis Report on Poor Wetability of PCB Pads<\/h2>\n<p>Next, let\u2019s turn to the analysis report on poor PCB pad wettability, a common issue in electronics manufacturing.<\/p>\n<h3>1. Sample Description<\/h3>\n<p>After conducting performance tests on a PCBA (Printed Circuit Board Assembly) prototype power supply, we discovered that the BGA (Ball Grid Array) components may have soldering defects (suspected cold solder joints). To resolve the issue, we conducted an analysis that primarily involved one PCBA sample and three PCB samples.<\/p>\n<h3>2. Analysis Process<\/h3>\n<ol>\n<li><strong>Trace Analysis<\/strong>\n<p>First, we performed microanalysis on the BGA components on the PCBA. We cut out the BGA components, then embedded them in epoxy resin, planed, polished, and etched them to examine the metallographic cross-sections of the BGA solder joints. At the fourth solder joint in the first row, we found clear signs of separation between the solder ball and the pad.<\/li>\n<li><strong>Analysis of PCB Pad Solderability<\/strong><\/li>\n<li><strong>Analysis of PCB Surface Conditions<\/strong><\/li>\n<li><strong>SEM and EDX Analysis<\/strong><\/li>\n<li><strong>Analysis of Solder Paste Wettability<\/strong><\/li>\n<\/ol>\n<h3>3. Conclusion<\/h3>\n<p>Based on the above analysis, we have reached the following conclusions:<\/p>\n<ul>\n<li>On the PCBA sample, the fourth solder joint in the BGA section of the first row has a defect; there is a clear open circuit between the solder ball and the pad.<\/li>\n<li>The cause of the open circuit is poor wetting (solderability) of the PCB pads; organic insulation and solder mask prevent the BGA solder balls from forming a metallized layer with the pads during soldering.<\/li>\n<\/ul>\n<p>This analytical report highlights the importance of PCB pad wettability and the potential issues that may arise during the electronics manufacturing process. Regular inspections and testing are critical steps in ensuring product quality and reliability.<\/p>\n<h2>Advanced: Six Root Causes of Poor Pad Wettability<\/h2>\n<p>Poor wettability is rarely caused by just one factor. In engineering practice, it is most efficient to troubleshoot by systematically examining the following six categories one by one:<\/p>\n<ul>\n<li><strong>Surface Condition of the Pad<\/strong>: Oxidation, organic contamination, solder mask residue, or incomplete development can all form a barrier layer;<\/li>\n<li><strong>Selection or Failure of Surface Treatments<\/strong>: OSP film is too thick or has expired; black plating on the gold-plated disk; oxidation of the spray-applied tin coating;<\/li>\n<li><strong>Solder Paste Issues<\/strong>: Metal content, flux activity, particle size, and storage conditions do not meet specifications;<\/li>\n<li><strong>Backflow Curve<\/strong>: Insufficient preheating, inadequate peak temperature, or too short a preheating time prevented the flux from being fully activated;<\/li>\n<li><strong>Pad Design<\/strong>: The pad size does not match the stencil aperture, or the pad is adjacent to a large copper area, resulting in insufficient local temperature;<\/li>\n<li><strong>Components and Incoming Materials<\/strong>: Pin oxidation; poor coplanarity of solder joints.<\/li>\n<\/ul>\n<div class=\"jp-tw\">\n<table>\n<thead>\n<tr>\n<th>Root Cause<\/th>\n<th>Typical Symptoms<\/th>\n<th>Verification Methods<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Pad Contamination \/ Organic Film<\/td>\n<td>Localized lack of wetting; the solder ball is concentrated on one side<\/td>\n<td>SEM\/EDX, Surface Energy Testing<\/td>\n<\/tr>\n<tr>\n<td>OSP is too thick or has expired<\/td>\n<td>Poor overall wetting; dark solder joints<\/td>\n<td>Coating Thickness Testing, Weldability Testing<\/td>\n<\/tr>\n<tr>\n<td>Insufficient Solubility of Solder Paste<\/td>\n<td>Rough solder joints and numerous solder balls<\/td>\n<td>Solder Paste Inspection, Wetting Balance<\/td>\n<\/tr>\n<tr>\n<td>Insufficient return temperature<\/td>\n<td>Local cold welds, incomplete welds<\/td>\n<td>Measured Furnace Temperature Curve<\/td>\n<\/tr>\n<tr>\n<td>Directly adjacent to the large copper heat-dissipating surface<\/td>\n<td>Some solder joints are not melted<\/td>\n<td>Surface Temperature Measured by a Thermocouple<\/td>\n<\/tr>\n<tr>\n<td>Pin Oxidation<\/td>\n<td>Some components are not properly secured<\/td>\n<td>Random Inspection of Incoming Materials for Appearance and Solderability<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"667\" height=\"376\" class=\"alignnone size-large wp-image-10145\" src=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/reasons-for-poor-soldering-of-circuit-boards.jpg\" alt=\"Poor Soldering on the Circuit Board\" srcset=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/reasons-for-poor-soldering-of-circuit-boards.jpg 667w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/reasons-for-poor-soldering-of-circuit-boards-300x169.jpg 300w\" sizes=\"auto, (max-width: 667px) 100vw, 667px\" \/><\/p>\n<p>For a more comprehensive classification of defects, see<a href=\"\/en\/blog\/pcb-soldering-defects-analysis-solutions\/\">Analysis of Causes and Solutions for PCB Soldering Defects<\/a>\u4e0e<a href=\"\/en\/blog\/smt-soldering-defects-solutions\/\">Analysis of SMT Soldering Defects and Solutions<\/a>\u3002<\/p>\n<h2>Advanced: How to Measure and Evaluate Wettability<\/h2>\n<p>If you encounter a suspected cold solder joint, we recommend following these six steps to gather evidence and avoid drawing conclusions based solely on experience:<\/p>\n<ol>\n<li><strong>Appearance and AOI<\/strong>: First, check the shape of the solder joints, the height of the solder wick, and whether there are any solder balls;<\/li>\n<li><strong>X-Ray<\/strong>: Hidden solder joints on BGAs, QFNs, and other packages must be inspected for voids, bridges, and open circuits;<\/li>\n<li><strong>Slice Analysis<\/strong>: Prepare metallographic sections of suspicious welds to examine whether the intermetallic compound (IMC) layer is continuous;<\/li>\n<li><strong>Surface Analysis<\/strong>: Use SEM\/EDX to determine whether there is an organic film or foreign matter on the surface of the pad;<\/li>\n<li><strong>Solderability Test<\/strong>: The wetting equilibrium method or tin-coating balance, which quantifies wetting force and wetting time;<\/li>\n<li><strong>Actual Furnace Temperature Measurements<\/strong>: Use a temperature-sensing plate to record the actual curve and verify that it matches the set value.<\/li>\n<\/ol>\n<p>To determine whether a solder joint is acceptable, the industry typically refers to<a href=\"\/en\/blog\/pcba-welding-standards\/\">PCBA Soldering Standards<\/a>Based on the visual inspection criteria,<a href=\"\/en\/blog\/12-suggestions-for-smt-processing-and-welding\/\">12 Tips for SMT Soldering<\/a>It also provides more specific operational guidelines.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"904\" height=\"664\" class=\"alignnone size-large wp-image-6787\" src=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/solder-joint-quality.jpg\" alt=\"Standard Requirements for Solder Joint Quality\" srcset=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/solder-joint-quality.jpg 904w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/solder-joint-quality-300x220.jpg 300w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/solder-joint-quality-768x564.jpg 768w\" sizes=\"auto, (max-width: 904px) 100vw, 904px\" \/><\/p>\n<h2>Advanced: Key Points to Consider When Tightening the Design After Increasing Density<\/h2>\n<p>As placement density increases, the margin for error regarding pads and layout decreases. The following requirements must be tightened accordingly:<\/p>\n<ul>\n<li><strong>Pad and Stencil Aperture<\/strong>: The aperture ratio, stencil thickness, and shape determine the amount of solder; fine-pitch components typically use thinner stencils and stepped apertures;<\/li>\n<li><strong>Device Spacing<\/strong>: Allow sufficient working space between the pick-and-place machine nozzle and the rework tool to prevent interference;<\/li>\n<li><strong>Devices Oriented in the Same Direction<\/strong>: For similar components, try to keep them in the same direction to reduce the number of times you need to change the nozzle or change direction, thereby improving efficiency;<\/li>\n<li><strong>Fiducial<\/strong>: Reference points must be provided both across the entire board and in specific areas to ensure placement alignment accuracy;<\/li>\n<li><strong>Thermal Balance Design<\/strong>: When a large copper surface is adjacent to small components, it can cause uneven temperature distribution; if necessary, provide thermal isolation or adjust the openings.<\/li>\n<\/ul>\n<div class=\"jp-tw\">\n<table>\n<thead>\n<tr>\n<th>Device pitch<\/th>\n<th>Wire Mesh Thickness<\/th>\n<th>Suggestions for Getting the Conversation Started<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>\u22650.65 mm<\/td>\n<td>0.12\u20130.15 mm<\/td>\n<td>Based on the 1:1 pad layout, fine-tuning is possible<\/td>\n<\/tr>\n<tr>\n<td>0.5 mm<\/td>\n<td>0.10\u20130.12 mm<\/td>\n<td>Abbreviate to prevent bridging<\/td>\n<\/tr>\n<tr>\n<td>0.4 mm or less<\/td>\n<td>0.08\u20130.10 mm<\/td>\n<td>Step or nano-coating, with strict control of tin content<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"1500\" height=\"844\" class=\"alignnone size-large wp-image-8904\" src=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/smt-solder-paste-printing-process-flow.jpg\" alt=\"SMT Solder Paste Printing Process Flow\" srcset=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/smt-solder-paste-printing-process-flow.jpg 1500w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/smt-solder-paste-printing-process-flow-300x169.jpg 300w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/smt-solder-paste-printing-process-flow-1024x576.jpg 1024w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/smt-solder-paste-printing-process-flow-768x432.jpg 768w\" sizes=\"auto, (max-width: 1500px) 100vw, 1500px\" \/><\/p>\n<h2>Advanced: Six Measures to Improve Welding Yield<\/h2>\n<ol>\n<li><strong>Include the requirements in the document<\/strong>: Pad dimensions, stencil apertures, and acceptable void rates, among other specifications, are clearly stated in the specifications;<\/li>\n<li><strong>First Item Confirmed<\/strong>: The first unit of each batch undergoes X-ray inspection and cross-section analysis; production is scaled up only after it has been approved;<\/li>\n<li><strong>Periodic Measurement of Furnace Temperature<\/strong>: Test each board type separately; do not simply reuse the old curves;<\/li>\n<li><strong>End-to-End Solder Paste Management<\/strong>: Records must be kept of refrigeration, thawing, mixing, and the expiration date;<\/li>\n<li><strong>Incoming Material Sampling Inspection<\/strong>: Random inspections of device pin oxidation and coplanarity, with particular attention to long-term inventory;<\/li>\n<li><strong>Data Closed-Loop<\/strong>: Tally AOI\/X-ray defects by pin number and pinpoint them to specific components or pads.<\/li>\n<\/ol>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"1100\" height=\"619\" class=\"alignnone size-large wp-image-8907\" src=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/solder-paste-for-smt-processing.jpg\" alt=\"SMT Solder Paste Basics\" srcset=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/solder-paste-for-smt-processing.jpg 1100w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/solder-paste-for-smt-processing-300x169.jpg 300w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/solder-paste-for-smt-processing-1024x576.jpg 1024w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/solder-paste-for-smt-processing-768x432.jpg 768w\" sizes=\"auto, (max-width: 1100px) 100vw, 1100px\" \/><\/p>\n<p>For information on the selection and management of solder paste, see<a href=\"\/en\/blog\/solder-paste-for-smt-processing\/\">Knowledge About Solder Paste for SMT Assembly<\/a>, For details on the printing process, see<a href=\"\/en\/blog\/smt-solder-paste-printing-process-flow\/\">SMT Solder Paste Printing Process Flow<\/a>\u3002<\/p>\n<h2>Conclusion<\/h2>\n<p>SMT technology offers significant advantages in modern electronics manufacturing, including high reliability, compact size, and excellent high-frequency performance. However, poor wettability of PCB pads can lead to soldering issues. Understanding these issues and taking appropriate measures is crucial for ensuring the quality of electronic products.<\/p>\n<h2>Frequently Asked Questions (FAQs)<\/h2>\n<h3>1. What is SMT technology?<\/h3>\n<p>SMT is a surface-mount technology that involves mounting components directly onto the surface of a PCB, rather than through through-hole insertion. It offers advantages such as compact size and high assembly density.<\/p>\n<h3>2. Why is the wettability of PCB pads important?<\/h3>\n<p>The wettability of PCB pads determines the quality of the solder joint; poor wettability can lead to soldering defects.<\/p>\n<h3>3. How can the wettability of PCB pads be improved?<\/h3>\n<p>To improve the wettability of PCB pads, you can use appropriate soldering processes and materials, ensure that the soldering surface is clean, and properly control the soldering temperature and time.<\/p>\n<h3>4. Why does SMT technology have good high-frequency performance?<\/h3>\n<p>SMT technology offers excellent high-frequency performance because it reduces the parasitic inductance and capacitance of components, thereby improving the high-frequency performance of the circuit.<\/p>\n<h3>5. How can problems in SMT soldering be resolved?<\/h3>\n<p>Resolving issues in SMT soldering requires careful analysis to identify the root cause of the problem, followed by appropriate measures, such as optimizing the soldering process or replacing materials.<\/p>\n<h3>6. How many voids are allowed in SMT solder joints?<\/h3>\n<p>According to common acceptance criteria, the void rate of BGA solder balls is generally required to be controlled at <strong>25%\u201330% and below<\/strong>, and for some high-reliability products, the tolerance will be tightened to 15%. The specific tolerance limits should be specified in the datasheet, and the results of X-ray spot checks shall prevail.<\/p>\n<h3>7. Why is X-ray inspection mandatory for BGAs?<\/h3>\n<p>Because the solder joints are located underneath the components, they cannot be detected during visual inspection or AOI. Short circuits, voids, insufficient solder, and open circuits can only be detected via X-ray; otherwise, these defects will not be revealed until the final assembly testing phase.<\/p>\n<h3>8. How do you choose the thickness of the wire mesh?<\/h3>\n<p>Determine based on the densest components on the board: for a pitch of \u22650.65 mm, use 0.12\u20130.15 mm; for 0.5 mm, use 0.10\u20130.12 mm; and for 0.4 mm and below, use 0.08\u20130.10 mm. When there are significant variations in component density on the same board, consider using a stepped stencil.<\/p>\n<h3>9. How long can solder paste be used after opening the package?<\/h3>\n<p>It is generally recommended to<strong>Within 24 hours<\/strong>Use as directed; refer to the solder paste specification sheet for details. Prolonged exposure after opening may cause moisture absorption and flux evaporation, resulting in poor printability and reduced solder joint quality. Any remaining solder paste should not be returned to the container and mixed with other batches.<\/p>\n<h3>10. Is there a big difference between lead-free and lead-based soldering in SMT?<\/h3>\n<p>The difference is significant. Lead-free solder has a higher melting point, requiring the peak reflow temperature to be increased by approximately 20\u201330\u00b0C. This places higher demands on the heat resistance of components and circuit boards, and its wettability is slightly poorer, which must be compensated for through flux activity and optimized temperature profiles.<\/p>\n<p><strong>Additional Information<\/strong>\uff1a<a href=\"\/en\/blog\/5-hdi-manufacturing-requirements\/\">5 Key Requirements and Optimization Strategies for the HDI Manufacturing Process<\/a> \u00b7 <a href=\"\/en\/faq\/smt-requires-customer-provided-information\/\">What information do customers need to provide before SMT assembly?<\/a><\/p>","protected":false},"excerpt":{"rendered":"<p>\u5728\u73b0\u4ee3\u7535\u5b50\u5236\u9020\u9886\u57df\uff0cSMT\u6280\u672f\uff08\u8868\u9762\u8d34\u88c5\u6280\u672f\uff09\u5df2\u7ecf\u6210\u4e3a\u4e3b\u6d41\u3002\u540c\u65f6\uff0cPCB\u710a\u76d8\u6da6\u6e7f\u6027\u5dee\u4e5f\u662f\u4e00\u4e2a\u5e38\u89c1\u7684\u95ee\u9898\u3002\u672c\u6587\u5c06 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":8901,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"slim_seo":{"title":"What Are the Advantages of SMT Technology? An Analysis of Reliability, Density, and High-Frequency Characteristics","description":"Why does SMT improve reliability and density? This article also analyzes the symptoms and causes of poor PCB pad wettability and provides a framework for improving solder joint quality. 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