{"id":2717,"date":"2026-10-15T09:00:00","date_gmt":"2026-10-15T01:00:00","guid":{"rendered":"https:\/\/www.jingpengpcb.com\/?p=2717"},"modified":"2026-10-08T20:14:42","modified_gmt":"2026-10-08T12:14:42","slug":"lpism-vs-dry-film-solder-mask","status":"publish","type":"post","link":"https:\/\/www.jingpengpcb.com\/en\/blog\/lpism-vs-dry-film-solder-mask\/","title":{"rendered":"What is the difference between liquid-phase solder mask and dry-film solder mask? A Comparison of Application Processes"},"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>Printed circuit board (PCB) manufacturing is an indispensable part of modern technology. Among the various processes involved, coating methods play a crucial role in PCB production. This article will take an in-depth look at several common PCB coating methods\u2014from dip coating to adhesive coating\u2014to provide you with an understanding of the important details of PCB manufacturing.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"1280\" height=\"720\" class=\"alignnone size-large wp-image-6562\" src=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/what-is-a-circuit-board-counterbore.jpg\" alt=\"What Are Blind Holes in Printed Circuit Boards?\" srcset=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/what-is-a-circuit-board-counterbore.jpg 1280w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/what-is-a-circuit-board-counterbore-300x169.jpg 300w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/what-is-a-circuit-board-counterbore-1024x576.jpg 1024w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/what-is-a-circuit-board-counterbore-768x432.jpg 768w\" sizes=\"auto, (max-width: 1280px) 100vw, 1280px\" \/><\/p>\n<h2>1. Solder Mask (S\/M)<\/h2>\n<p>Although the term is commonly used in <strong>Solder Mask<\/strong>, but the more formal way to say it is<strong>Solder Resist<\/strong>. Solder mask refers to the process of covering areas on the surface of a printed circuit board that are not intended for soldering with a permanent resin film. This film, known as S\/M, not only prevents solder from adhering to these areas but also provides protection and insulation.<\/p>\n<p>Only by breaking down and explaining the four functions of this layer can we understand why it is the most \u201cthankless\u201d layer on a PCB:<\/p>\n<ul>\n<li><strong>Solder Mask<\/strong>: During soldering, it prevents molten solder paste from flowing to areas where it shouldn\u2019t be, thereby avoiding bridging and short circuits. This is where its name comes from, and it is also its core function.<\/li>\n<li><strong>Insulation Protection<\/strong>: Shields against air, moisture, and contaminants to prevent oxidation of the copper surface and electrochemical migration (CAF).<\/li>\n<li><strong>Mechanical Protection<\/strong>: Prevent scratches on the wiring during handling and assembly.<\/li>\n<li><strong>Appearance and Logos<\/strong>: Provides the panel color (green, black, white, blue, red, etc.) and serves as a base for subsequent character printing.<\/li>\n<\/ul>\n<h2>2. Liquid Photoimaginable Solder Mask (LPSM)<\/h2>\n<p><strong>LPSM<\/strong>This is a solder mask used on the surface of printed circuit boards. It is particularly suitable for fine-line circuit boards. Traditional screen-printed, oven-cured epoxy solder masks can no longer meet the requirements of these fine-line boards. Therefore, LPSM was developed. After squeegeeing and partial curing, you can use a negative film for precise alignment and exposure, followed by development and full curing, ultimately resulting in a solder mask with accurate positioning. Having withstood years of mass production testing, LPSM offers highly reliable quality and has become the mainstream choice among various solder masks.<\/p>\n<p>The fundamental reason LPSM has replaced thermosetting green screen printing ink is<strong>Alignment Accuracy<\/strong>: Screen printing relies on the screen for positioning, with an accuracy typically ranging from \u00b1150 to 200 \u03bcm; LPSM uses exposure imaging, achieving alignment accuracy of \u00b150 \u03bcm or better (up to \u00b125 \u03bcm when combined with LDI). When the pad spacing falls below 0.5 mm, screen printing can no longer guarantee that the pads will not be covered.<\/p>\n<h2>3. Four coating methods: curtain coating, roller coating, spray coating, and film lamination<\/h2>\n<h3>3.1 Curtain Coating (Curtain Coating Method)<\/h3>\n<p><strong>The Liantu Method<\/strong>This is an automated method for applying photosensitive green paint to the surface of a circuit board. This coating method uses a thinned, non-water-soluble green paint ink. During the process, the green paint flows continuously in a water curtain-like manner from a long, narrow opening, striking the surface of the board at a right angle as it moves forward on an automated conveyor. This ensures that a uniform layer of ink is applied to the board surface. Once the solvent has evaporated and the ink has partially cured, the board must be flipped and the other side treated to facilitate image transfer via the photolithographic process. Although the cascade coating method is not new to the printed circuit board industry, it provides an efficient coating method for PCB manufacturing.<\/p>\n<h3>3.2 Roller Coating<\/h3>\n<p><strong>Roll Coating Method<\/strong>Green paint or photosensitive circuit ink is applied to the surface of the circuit board using rollers. This is followed by semi-curing, exposure, and development. This method is particularly advantageous for low-cost, high-volume circuit boards.<\/p>\n<h3>3.3 Spray Coating (Spray Coating Method)<\/h3>\n<p><strong>Spray Coating Method<\/strong>Compressed air is used to spray liquid coating onto the surface of the object being treated. This method is similar to conventional \u201cspray painting.\u201d It can also be combined with an electrostatic device to charge the atomized liquid spray, allowing it to adhere evenly to the surface of the object being treated. This technique is also used in the application of green paint to circuit boards.<\/p>\n<p>A Comparative Analysis of Three Liquid Coating Methods and Dry Film Laminating:<\/p>\n<div class=\"jp-tw\">\n<table>\n<thead>\n<tr>\n<th>Coating Method<\/th>\n<th>Thickness Uniformity<\/th>\n<th>Filling Capacity<\/th>\n<th>Panel Compatibility<\/th>\n<th>Equipment Costs<\/th>\n<th>Applicable Scenarios<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Curtain Coating (Curtain)<\/td>\n<td>\u4f18<\/td>\n<td>\u4e2d<\/td>\n<td>Mainly flat, rigid panels<\/td>\n<td>\u9ad8<\/td>\n<td>Large quantities of rigid circuit boards with strict requirements for thickness consistency<\/td>\n<\/tr>\n<tr>\n<td>Roller Application<\/td>\n<td>\u826f<\/td>\n<td>\u4e2d<\/td>\n<td>Flat plate, sensitive to warping<\/td>\n<td>\u4e2d<\/td>\n<td>Price-sensitive high-volume boards<\/td>\n<\/tr>\n<tr>\n<td>Spray Coating<\/td>\n<td>\u826f<\/td>\n<td>\u4f18<\/td>\n<td>Unevenness, thick copper, high aspect ratio<\/td>\n<td>Upper-middle<\/td>\n<td>Thick copper boards, boards with significant height differences<\/td>\n<\/tr>\n<tr>\n<td>Dry Film<\/td>\n<td>Excellent (determined by the membrane material)<\/td>\n<td>\u5dee<\/td>\n<td>On flat panels, bubbles are likely to form in concave areas.<\/td>\n<td>\u4f4e<\/td>\n<td>Standard Boards, Inner Layers, Simple Outlines<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>The criteria are straightforward:<strong>The more uneven the board surface and the thicker the copper, the more necessary it is to use spray coating.<\/strong>; For flat panels, large batches, and cost-sensitive applications, roller or curtain coating is more cost-effective; dry film, on the other hand, offers the advantage of thickness determined by the film material and the best consistency, but has the poorest coverage capability.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"1110\" height=\"624\" class=\"alignnone size-large wp-image-9350\" src=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2024\/01\/8-issues-for-pcb-copper-clad-coating.jpg\" alt=\"8 Things to Keep in Mind When Applying Copper to a PCB\" srcset=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2024\/01\/8-issues-for-pcb-copper-clad-coating.jpg 1110w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2024\/01\/8-issues-for-pcb-copper-clad-coating-300x169.jpg 300w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2024\/01\/8-issues-for-pcb-copper-clad-coating-1024x576.jpg 1024w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2024\/01\/8-issues-for-pcb-copper-clad-coating-768x432.jpg 768w\" sizes=\"auto, (max-width: 1110px) 100vw, 1110px\" \/><\/p>\n<h2>4. Key Comparison: Liquid Photoresist Solder Mask vs. Dry Film Solder Mask<\/h2>\n<p>This is the question the title of this article seeks to answer. It is not simply a matter of one being better than the other, but rather that they are applicable in different contexts:<\/p>\n<div class=\"jp-tw\">\n<table>\n<thead>\n<tr>\n<th>Comparison Items<\/th>\n<th>Liquid Photoresist Solder Mask (LPSM)<\/th>\n<th>Dry Film Solder Mask<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Film Formation Method<\/td>\n<td>Pre-baking (partial curing) after applying liquid ink<\/td>\n<td>Vacuum Film Application with Hot Roller Pressing<\/td>\n<\/tr>\n<tr>\n<td>Typical Film Thickness<\/td>\n<td>8\u201325 \u03bcm (adjustable as needed)<\/td>\n<td>Determined by the membrane material specifications; typically 25\u201350 \u03bcm<\/td>\n<\/tr>\n<tr>\n<td>Alignment Accuracy<\/td>\n<td>Excellent; can be used with LDI for precise alignment<\/td>\n<td>Liang, due to limitations in film tension and registration accuracy<\/td>\n<\/tr>\n<tr>\n<td>Filling Capacity<\/td>\n<td>Advantage: Adapts to uneven surfaces and height differences<\/td>\n<td>Poor; air bubbles tend to remain in the recesses.<\/td>\n<\/tr>\n<tr>\n<td>Fine-pitch Capabilities<\/td>\n<td>Excellent; can handle pitch sizes of 0.3 mm or less<\/td>\n<td>Generally, the film thickness limits the resolution.<\/td>\n<\/tr>\n<tr>\n<td>Resistance to Electroplating\/Chemical Resistance<\/td>\n<td>Good (depending on whether it was baked thoroughly afterward)<\/td>\n<td>\u4f18<\/td>\n<\/tr>\n<tr>\n<td>Production Cycle<\/td>\n<td>Requires pre-baking, exposure, development, and post-baking; the process is lengthy<\/td>\n<td>Just apply the film\u2014it\u2019s quick and easy.<\/td>\n<\/tr>\n<tr>\n<td>Cost<\/td>\n<td>High (Materials + Equipment + Labor)<\/td>\n<td>\u4f4e<\/td>\n<\/tr>\n<tr>\n<td>Typical Applications<\/td>\n<td>Fine-line PCBs, HDI, High-Density BGA, Rigid-Flex PCBs<\/td>\n<td>Standard boards, inner layers, and boards requiring high thickness consistency<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>In a nutshell:<strong>Liquid solder mask excels in precision and coverage, while dry-film solder mask excels in efficiency and consistency.<\/strong>. As pad spacing continues to shrink, liquid-phase photosensitive solder mask has become the mainstream choice for outer layers; dry film solder mask is primarily used for inner layers and cost-sensitive standard boards. For a complete surface treatment system, see<a href=\"\/en\/capabilities\/pcb-surface-finishes\/\">PCB Surface Treatment Processes<\/a>\u3002<\/p>\n<h2>5. Encroachment<\/h2>\n<p>In the printed circuit board industry,<strong>Encroachment<\/strong>This is a technical term. It refers to the accidental appearance of green solder mask marks on areas of solder pads that should not be coated, such as the walls of the holes in through-hole components or the solder pads on SMT (Surface Mount Technology) boards. This condition can severely affect solder performance during downstream assembly, which is why it is specifically referred to as \u201cencroachment.\u201d<\/p>\n<p>Encroachment is one of the most common and most critical defects in the solder mask process\u2014it directly renders the pads unsolderable and is often not detected until after SMT, resulting in extremely high rework costs. Common solder mask defects and countermeasures:<\/p>\n<div class=\"jp-tw\">\n<table>\n<thead>\n<tr>\n<th>Defects<\/th>\n<th>Performance<\/th>\n<th>Main Reasons<\/th>\n<th>Countermeasures<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Encroachment (Upper Pad)<\/td>\n<td>There is green paint residue on the pad.<\/td>\n<td>Misalignment, incomplete development, insufficient exposure energy<\/td>\n<td>Improve registration accuracy, monitor development spots, and calibrate exposure energy<\/td>\n<\/tr>\n<tr>\n<td>Bubbles \/ Voids<\/td>\n<td>There are bubbles in the solder mask layer<\/td>\n<td>Air bubbles and dents on the screen surface when applying the screen protector<\/td>\n<td>Switch to spray coating or vacuum film application, and enhance pretreatment<\/td>\n<\/tr>\n<tr>\n<td>Solder Mask Bubbling and Peeling<\/td>\n<td>Solder Mask Bulging After Reflow Soldering<\/td>\n<td>Inadequate pretreatment, contamination on the board surface, and insufficient post-baking<\/td>\n<td>Reinforce the grinding plate\/micro-etching; increase the post-baking temperature and duration<\/td>\n<\/tr>\n<tr>\n<td>Incomplete Development (Residual Toner)<\/td>\n<td>There is a hazy film residue between the pads<\/td>\n<td>Insufficient developer concentration or temperature; insufficient spray pressure<\/td>\n<td>Monitor the development point at 40\u201360%; change the tank solution periodically.<\/td>\n<\/tr>\n<tr>\n<td>Solder mask is too thin<\/td>\n<td>Insufficient wire insulation coverage, reduced voltage withstand<\/td>\n<td>Insufficient coating thickness, excessive copper thickness<\/td>\n<td>Increase the coating amount or switch to spraying; control the copper thickness<\/td>\n<\/tr>\n<tr>\n<td>Color Variation \/ Uneven Gloss<\/td>\n<td>Color inconsistencies within the same batch of panels<\/td>\n<td>Variations in ink batches, uneven post-printing curing temperatures<\/td>\n<td>Use ink from the same batch with the same lot number and calibrate the oven temperature profile<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p>For common issues with the \"Green Window\" (open-window) design, see<a href=\"\/en\/blog\/green-oil-plugging\/\">Common Issues in PCB Solder Mask Window Design<\/a>\u3002<\/p>\n<h2>6. Post-Cure (Follow-up Curing, Post-Baking)<\/h2>\n<p>In the printed circuit board industry, liquid photosensitive green solder mask or solder resist dry film requires further curing after development to enhance its solderability. This process is called<strong>Post-curing<\/strong>. In addition, for multilayer printed circuit boards, particularly those made of polyimide, it is also necessary to perform the following after lamination:<strong>Bake later<\/strong>, to ensure that the polymerization reaction is complete.<\/p>\n<p>The importance of post-baking is often underestimated. Although the solder mask has formed by the end of the development process, the cross-linking reaction is not yet complete; at this stage, its chemical resistance, hardness, and adhesion are all insufficient. Post-baking (typical conditions: 150 \u00b0C for 60\u201390 minutes, depending on the ink specification) increases the degree of cross-linking to 90% or higher, thereby ensuring:<\/p>\n<ul>\n<li><strong>Resistance to thermal shock during welding<\/strong>: Withstands lead-free reflow at temperatures above 260 \u00b0C without bubbling or cracking.<\/li>\n<li><strong>Chemical Resistance<\/strong>: Resistant to subsequent surface treatment solutions, flux, and cleaning agents.<\/li>\n<li><strong>Insulation Resistance<\/strong>: Only when the cross-linked membrane layer has a low moisture absorption rate can the surface insulation resistance (SIR) meet the required standards.<\/li>\n<li><strong>Long-Term Reliability<\/strong>: Reduces cracking and delamination under temperature and humidity cycling.<\/li>\n<\/ul>\n<h2>7. Tackiness<\/h2>\n<p>**Tackiness** has two meanings in printed circuit board manufacturing. First, it refers to the property of whether the board remains tacky to the film under strong light after the liquid photosensitive green mask (LPSM) has been applied. Second, it is also used to describe the printing on the solder pads of SMDs (surface-mount devices).<a href=\"\/en\/smt-factory\/\">Solder Paste<\/a>During this process, the solder paste must possess a certain degree of adhesion and positioning capability.<\/p>\n<p>The first issue relates to a practical challenge on the production line: After LPSM coating, a pre-bake (partial curing) is required. If the pre-bake is insufficient, the surface remains tacky, causing the film (or the LDI contact surface) to stick to the board during exposure. At best, this contaminates the film; at worst, it tears the coating, resulting in the entire batch being scrapped. The key control factor is matching the pre-bake temperature and time\u2014if the temperature is too high, development becomes difficult (over-baking), so the process window is very narrow. It is essential to follow the ink specification sheet and perform a first-article verification.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"1280\" height=\"720\" class=\"alignnone size-large wp-image-8586\" src=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/comparison-between-ldi-and-ccd-exposure-machines.jpg\" alt=\"A Comparison of LDI and CCD Exposure Systems\" srcset=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/comparison-between-ldi-and-ccd-exposure-machines.jpg 1280w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/comparison-between-ldi-and-ccd-exposure-machines-300x169.jpg 300w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/comparison-between-ldi-and-ccd-exposure-machines-1024x576.jpg 1024w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/comparison-between-ldi-and-ccd-exposure-machines-768x432.jpg 768w\" sizes=\"auto, (max-width: 1280px) 100vw, 1280px\" \/><\/p>\n<p>These terms and coating methods play an important role in circuit board manufacturing. A thorough understanding of them helps provide insight into the complexity and innovation involved in circuit board production.<\/p>\n<h2>8. Solder Mask Cutouts and Alignment: Essential Requirements in the Era of Fine Pitch<\/h2>\n<p>With the widespread adoption of BGA, CSP, and fine-pitch QFP packages, the precision requirements for solder mask openings have reached new heights. Four key parameters:<\/p>\n<ul>\n<li><strong>Window Opening Methods<\/strong>: SMD (solder mask-defined pads, with green solder mask applied to the edges of the pads) and NSMD (non-solder mask-defined pads, with openings larger than the pads). BGAs typically use NSMD, where the pads are defined by copper foil, resulting in higher reliability.<\/li>\n<li><strong>Window Tolerance<\/strong>: Standard \u00b150 \u03bcm; for fine-pitch applications, within \u00b125 \u03bcm.<\/li>\n<li><strong>Solder Mask Dam<\/strong>: The width of the green solder mask left between adjacent pads. For a BGA with a pitch of 0.4 mm, the solder mask barrier must be \u226575 \u03bcm; for a pitch of 0.3 mm, it must be \u226550 \u03bcm. If the barrier is too narrow, it may peel off due to insufficient adhesion.<\/li>\n<li><strong>Alignment Methods<\/strong>: Traditional photomasks rely on manual or CCD alignment, whereas LDI directly images the design data and can compensate for scaling, making it the obvious choice for fine-pitch designs.<\/li>\n<\/ul>\n<h2>9. Inspection: How to Verify That the Solder Mask Is Actually Compliant<\/h2>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"152\" height=\"85\" class=\"alignnone size-large wp-image-9962\" src=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2024\/11\/lpsalpine.png\" alt=\"Liquid Photosensitive Solder Mask Coating\" srcset=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2024\/11\/lpsalpine.png 152w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2024\/11\/lpsalpine-150x85.png 150w\" sizes=\"auto, (max-width: 152px) 100vw, 152px\" \/><\/p>\n<p>The solder mask is the final organic coating applied to the entire board; since problems often arise at this final stage, it is essential to ensure quality control before the product leaves the factory:<\/p>\n<ul>\n<li><strong>Full Visual Inspection<\/strong>: Check for excess solder, bubbles, scratches, color variations, and foreign objects.<\/li>\n<li><strong>Thickness Measurement<\/strong>: Measure the solder mask thickness using a thickness gauge or by cutting a cross-section; the thickness at the line edges must not be less than the specified value (generally \u22658 \u03bcm).<\/li>\n<li><strong>Adhesion Test<\/strong>: A tape test (cross-hatch method) confirms that the coating does not peel off.<\/li>\n<li><strong>Hardness Testing<\/strong>: Pencil hardness is generally required to be \u22656H.<\/li>\n<li><strong>Solvent Resistance and Solderability<\/strong>: The tin-plating test confirms good pad wetting, which is the final method for verifying encroachment.<\/li>\n<li><strong>12 Ink Performance Metrics<\/strong>: For the complete set of indicators, see<a href=\"\/en\/blog\/12-pcb-ink-technical-performance-indicators\/\">12 Key Technical Performance Metrics for PCB Ink<\/a>\u3002<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" width=\"1280\" height=\"720\" class=\"alignnone size-large wp-image-8571\" src=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/osp-surface-treatment-process-for-circuit-boards.jpg\" alt=\"OSP Surface Treatment Process for Printed Circuit Boards\" srcset=\"https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/osp-surface-treatment-process-for-circuit-boards.jpg 1280w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/osp-surface-treatment-process-for-circuit-boards-300x169.jpg 300w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/osp-surface-treatment-process-for-circuit-boards-1024x576.jpg 1024w, https:\/\/www.jingpengpcb.com\/wp-content\/uploads\/2023\/08\/osp-surface-treatment-process-for-circuit-boards-768x432.jpg 768w\" sizes=\"auto, (max-width: 1280px) 100vw, 1280px\" \/><\/p>\n<p>When introducing solder mask processes into new projects, following these four steps for selection can help avoid most issues that may arise later:<\/p>\n<ol>\n<li><strong>Kanban Board Status<\/strong>: For flat boards, dry film or roller application may be considered; boards with thick copper or significant height differences must be spray-coated.<\/li>\n<li><strong>Check the spacing requirements<\/strong>: For pad spacing \u22650.5 mm, dry film is acceptable; for spacing less than 0.4 mm, liquid photoresist solder mask + LDI must be used.<\/li>\n<li><strong>See the post-production process<\/strong>: If subsequent processes such as lead-free reflow, multiple reflow cycles, or chemical gold plating are involved, the post-baking temperature and ink chemical resistance requirements must be correspondingly increased.<\/li>\n<li><strong>View the Acceptance Criteria<\/strong>: Specify the grade in accordance with IPC-SM-840 or customer specifications, and include thickness, adhesion, and hardness in the inspection criteria.<\/li>\n<\/ol>\n<p>Four process windows that require daily monitoring on the production line:<\/p>\n<ul>\n<li><strong>Pre-bake Window<\/strong>: Follow the ink specification sheet for temperature and time settings; over-baking makes development difficult, while under-baking causes the ink to stick to the film. Verify by printing the first piece of each shift.<\/li>\n<li><strong>Exposure Energy<\/strong>: Calibrate daily using a Stouffer light bar; energy drift is the primary cause of top-pad defects and incomplete development.<\/li>\n<li><strong>Development Point<\/strong>: Maintain the level between 40 and 60%, and conduct regular checks of the spray pressure and bath concentration.<\/li>\n<li><strong>Temperature Distribution in the Post-Bake Chamber<\/strong>: Conduct regular temperature uniformity tests on the oven; excessive temperature variations are the primary cause of color variations within the same batch and uneven cross-linking.<\/li>\n<\/ul>\n<h2>Conclusion<\/h2>\n<p>Printed circuit board manufacturing is a field full of technical challenges and innovation. From dip coating to spray coating, various coating methods offer a wide range of options for printed circuit boards to meet different needs. At the same time, controlling the adhesion and quality of the solder mask is crucial for ensuring the performance of printed circuit boards. With the continuous advancement of technology, the future of printed circuit board manufacturing remains bright and full of potential.<\/p>\n<h2>Frequently Asked Questions<\/h2>\n<h3>1. What is the circuit board coating method?<\/h3>\n<p>The circuit board coating process involves applying green paint or solder mask to the surface of a circuit board to protect and isolate the conductive areas.<\/p>\n<h3>2. Why is encroachment so important in PCB manufacturing?<\/h3>\n<p>Encroachment can affect solder performance and may lead to soldering issues; therefore, it requires special attention in circuit board manufacturing.<\/p>\n<h3>3. What is LPSM?<\/h3>\n<p>LPSM is a liquid, photosensitive solder mask in green, used on the surface of printed circuit boards; it is particularly suitable for boards with fine lines.<\/p>\n<h3>4. Why are post-curing and post-baking required in circuit board manufacturing?<\/h3>\n<p>Post-curing and post-baking can enhance the physical properties and solderability of the coating, ensuring the performance of the circuit board.<\/p>\n<h3>5. Why is tackiness important?<\/h3>\n<p>Tackiness affects the properties of the coating, including its adhesion during the coating process and the adhesion of solder paste to SMD pads. These properties influence the quality and performance of printed circuit board manufacturing.<\/p>\n<h3>6. Liquid solder mask or dry film solder mask\u2014which one should you choose for standard circuit boards?<\/h3>\n<p>For standard boards (pad spacing \u22650.5 mm, flat board surface), dry film is more cost-effective, offers a shorter process, and provides better thickness consistency. However, when dealing with fine-pitch designs, dense BGAs, thick copper, or boards with significant surface variations, liquid photoresist solder mask must be used, as dry film cannot provide sufficient coverage or resolution.<\/p>\n<h3>7. Does the color of the solder mask affect performance?<\/h3>\n<p>There are subtle differences. Green is the most commonly used color and offers the best contrast for both AOI and visual inspection; black and white are often used for consumer-grade cosmetic parts, but black can reduce AOI detection rates, while white tends to show dirt more easily. A matte finish is more prone to showing fingerprints and scratches than a glossy finish. There is little difference in performance; the main impact is on inspection efficiency and appearance.<\/p>\n<h3>8. What are the consequences of a solder mask barrier that is too narrow?<\/h3>\n<p>When the width of the solder mask barrier is less than 50 \u03bcm, the contact area between the green solder mask and the substrate is insufficient, making it prone to peeling off entirely during reflow soldering or subsequent thermal processes. Once peeled off, isolation between adjacent pads is lost, significantly increasing the risk of bridging. During design, it is better to reduce the size of the pads than to push the solder mask barrier to its limit.<\/p>\n<h3>9. What are the signs of insufficient post-baking?<\/h3>\n<p>There are three typical issues: bubbling or whitening of the solder mask during reflow soldering; discoloration of the solder mask caused by penetration of surface treatment chemicals; and failure to meet surface insulation resistance (SIR) test standards. Excessively high post-bake temperatures are also problematic, as they can cause the coating to become brittle and prone to cracking; therefore, it is essential to follow the ink specification sheet.<\/p>\n<h3>10. What solder mask process is used for flexible circuits?<\/h3>\n<p>Flexible circuits typically use liquid photosensitive solder resist (PSR) or coverlay. Coverlay consists of a polyimide film with an adhesive layer; it offers better flexibility than ink and is the preferred choice for flexible areas, while ink is used for non-flexible areas and fine pads. Both can be used in combination; for specific process details, see<a href=\"\/en\/blog\/fpc-flexible-circuit-solder-mask-process\/\">A Detailed Explanation of the Solder Mask Process for FPC Flexible Printed Circuit Boards<\/a>\u3002<\/p>\n<p><strong>Related Processes<\/strong>\uff1a<a href=\"\/en\/blog\/application-of-uv-laser-in-circuit-board-production\/\">Applications of Ultraviolet Lasers in Printed Circuit Board Manufacturing<\/a> \u00b7 <a href=\"\/en\/blog\/multilayer-circuit-board-vs-double-sided-board\/\">Characteristics of Multilayer Printed Circuit Boards and How They Differ from Double-Sided Boards<\/a> \u00b7 <a href=\"\/en\/capabilities\/pcb-surface-finishes\/\">PCB Surface Treatment Processes<\/a><\/p>","protected":false},"excerpt":{"rendered":"<p>\u7535\u8def\u677f\u5236\u9020\u662f\u73b0\u4ee3\u79d1\u6280\u9886\u57df\u4e2d\u4e0d\u53ef\u6216\u7f3a\u7684\u4e00\u90e8\u5206\u3002\u5176\u4e2d\uff0c\u6d82\u88c5\u6cd5\u5728\u7535\u8def\u677f\u751f\u4ea7\u8fc7\u7a0b\u4e2d\u53d1\u6325\u7740\u5173\u952e\u4f5c\u7528\u3002\u672c\u6587\u5c06\u6df1\u5165\u63a2\u8ba8\u51e0\u79cd\u5e38 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":6562,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"slim_seo":{"title":"What is the difference between liquid-phase solder mask and dry-film solder mask? A Comparison of Application Processes","description":"What is the difference between liquid photosensitive solder mask and dry film solder mask? Explain the meanings of terms such as \"dip coating\" and \"roll coating,\" as well as \"post-bake curing.\" By checking your work against the checklist in this article, you can avoid one round of rework on your prototype."},"_slim_seo_primary_term_category":0,"_slim_seo_primary_term_post_tag":0,"footnotes":""},"categories":[409,26],"tags":[],"class_list":["post-2717","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-smt-assembly","category-blog"],"_links":{"self":[{"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/posts\/2717","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/comments?post=2717"}],"version-history":[{"count":5,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/posts\/2717\/revisions"}],"predecessor-version":[{"id":19886,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/posts\/2717\/revisions\/19886"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/media\/6562"}],"wp:attachment":[{"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/media?parent=2717"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/categories?post=2717"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.jingpengpcb.com\/en\/wp-json\/wp\/v2\/tags?post=2717"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}