{"id":18114,"date":"2025-12-31T18:23:30","date_gmt":"2025-12-31T10:23:30","guid":{"rendered":"https:\/\/www.bestpcbs.com\/blog\/?p=18114"},"modified":"2025-12-31T18:24:08","modified_gmt":"2025-12-31T10:24:08","slug":"2oz-thicker-copper-rigid-flex-pcb-manufacturing-challenges","status":"publish","type":"post","link":"https:\/\/www.bestpcbs.com\/blog\/2025\/12\/2oz-thicker-copper-rigid-flex-pcb-manufacturing-challenges\/","title":{"rendered":"2oz Thicker Copper Rigid-Flex PCB Manufacturing &#038; Challenges"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_82_2 ez-toc-wrap-left counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.bestpcbs.com\/blog\/2025\/12\/2oz-thicker-copper-rigid-flex-pcb-manufacturing-challenges\/#Project_Introduction\" >Project Introduction<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.bestpcbs.com\/blog\/2025\/12\/2oz-thicker-copper-rigid-flex-pcb-manufacturing-challenges\/#Material_Structure_and_Key_Design_Parameters\" >Material Structure and Key Design Parameters<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.bestpcbs.com\/blog\/2025\/12\/2oz-thicker-copper-rigid-flex-pcb-manufacturing-challenges\/#Why_This_Rigid-Flex_PCB_Was_Inherently_Difficult\" >Why This Rigid-Flex PCB Was Inherently Difficult?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.bestpcbs.com\/blog\/2025\/12\/2oz-thicker-copper-rigid-flex-pcb-manufacturing-challenges\/#Technical_Challenge_1_Thick_Copper_Etching_with_Narrow_Spacing\" >Technical Challenge #1: Thick Copper Etching with Narrow Spacing<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.bestpcbs.com\/blog\/2025\/12\/2oz-thicker-copper-rigid-flex-pcb-manufacturing-challenges\/#Technical_Challenge_2_Annular_Ring_Integrity_in_Plated_Through_Holes\" >Technical Challenge #2: Annular Ring Integrity in Plated Through Holes<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/www.bestpcbs.com\/blog\/2025\/12\/2oz-thicker-copper-rigid-flex-pcb-manufacturing-challenges\/#Technical_Challenge_3_Stiffener_Bonding_Alignment_and_Adhesive_Overflow\" >Technical Challenge #3: Stiffener Bonding, Alignment, and Adhesive Overflow<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/www.bestpcbs.com\/blog\/2025\/12\/2oz-thicker-copper-rigid-flex-pcb-manufacturing-challenges\/#DFM_Guidelines_for_Rigid-Flex_PCB_Designers\" >DFM Guidelines for Rigid-Flex PCB Designers<\/a><\/li><\/ul><\/nav><\/div>\n<div class=\"yzp-no-index\"><\/div>\n<p>Recently, Best Technology faced a huge challenge in a 2oz copper <a href=\"https:\/\/www.bestfpc.com\/Products\/Rigid_Flex_PCB\/\">rigid flex PCB manufacturing<\/a>, this board appeared simple on the drawing but revealed multiple layers of engineering challenges once entering mass production. But finally, we finished this project very well and overcome this challenge, let\u2019s see what are the challenges on this project and how does our team overcome them!<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Project_Introduction\"><\/span>Project Introduction<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>The board used a 70\/25 double-sided adhesive ED flexible substrate with PI25\/AD50 coverlay, coupled with a 2+2 layers dual access structure that required thick copper, small annular rings, narrow spacings, and FR4 stiffeners with extremely limited clearance. Each of these parameters independently creates difficulty, but combined, they demand precise collaboration between engineering, fabrication, and process control.<\/p>\n\n\n\n<p>This article explains:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Why the design was inherently difficult<\/li>\n\n\n\n<li>What manufacturing risks were present<\/li>\n\n\n\n<li>How our engineering team solved each challenge<\/li>\n\n\n\n<li>What PCB designers should avoid in similar projects<\/li>\n\n\n\n<li>Why Best Technology can manufacture such <a href=\"https:\/\/www.bestpcbs.com\/blog\/2025\/12\/2oz-thicker-copper-rigid-flex-pcb-manufacturing-challenges\/\">high-reliability rigid-flex PCBs<\/a><\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Material_Structure_and_Key_Design_Parameters\"><\/span>Material Structure and Key Design Parameters<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>The board consisted of the following:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Flexible substrate: 70\/25 double-sided adhesive ED copper<\/li>\n\n\n\n<li>Coverlay: PI 25 \u00b5m + Adhesive 50 \u00b5m<\/li>\n\n\n\n<li>Base copper: <strong>2 oz copper<\/strong><\/li>\n\n\n\n<li>Layer count: Four-layer rigid-flex structure<\/li>\n\n\n\n<li>Critical routing: 0.15 mm minimum trace\/space<\/li>\n\n\n\n<li>Plated hole: 0.66 mm with hole spacing of only 0.60 mm<\/li>\n\n\n\n<li>Annular ring: 0.05 mm on certain pads<\/li>\n\n\n\n<li>Stiffener: FR4 stiffener with 0.95 mm stiffener hole and 0.31 mm ribs<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-image size-full\"><a href=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2025\/12\/Material-Structure-and-Key-Design-Parameters.png\"><img decoding=\"async\" src=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2025\/12\/Material-Structure-and-Key-Design-Parameters.png\" alt=\"Material Structure and Key Design Parameters\" class=\"wp-image-18121\"\/><\/a><\/figure>\n\n\n\n<p>This combination is common in advanced <strong>HDI rigid-flex PCB manufacturing<\/strong>, yet its manufacturability depends heavily on copper behavior, adhesive flow, and drilling tolerances.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Why_This_Rigid-Flex_PCB_Was_Inherently_Difficult\"><\/span>Why This Rigid-Flex PCB Was Inherently Difficult?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p><strong>1. Thick copper increases side-etching risk<\/strong><\/p>\n\n\n\n<ol class=\"wp-block-list\"><\/ol>\n\n\n\n<p>With 2 oz copper, the etching rate is higher and lateral etch\u2014often called side-etch\u2014is harder to control. In this case, the side-etching amount reached: 0.0070 \u00b1 0.003 mm. For ultra-fine traces in a <strong><a href=\"https:\/\/www.bestpcbs.com\/blog\/2025\/12\/2oz-thicker-copper-rigid-flex-pcb-manufacturing-challenges\/\">rigid-flex PCB design<\/a><\/strong>, this will eat into the design margin.<\/p>\n\n\n\n<p><strong>2. Small annular rings compromise via reliability<\/strong><\/p>\n\n\n\n<p>Pads with 0.05 mm annular ring severely restrict drilling tolerance. In <strong>flex-rigid PCB fabrication<\/strong>, annular rings below 0.10 mm are classified as high-risk features.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><a href=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2025\/12\/f2114e56e5a44d3abaf1144eb9793f9f.png\"><img decoding=\"async\" src=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2025\/12\/f2114e56e5a44d3abaf1144eb9793f9f.png\" alt=\"Why This Rigid-Flex PCB Was Inherently Difficult?\" class=\"wp-image-18122\"\/><\/a><\/figure>\n\n\n\n<p><strong>3. Extremely tight stiffener clearance<\/strong><\/p>\n\n\n\n<p>The stiffener needed:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u00b10.20 mm placement tolerance<\/li>\n\n\n\n<li>\u00b10.05 mm drilling tolerance<\/li>\n<\/ul>\n\n\n\n<p>But the designer only left 0.15 mm clearance, causing a mismatch between <strong>rigid-flex PCB stiffener<\/strong> alignment tolerance and actual manufacturing capability.<\/p>\n\n\n\n<p><strong>4. Thin FR4 stiffener ribs cause glue overflow<\/strong><\/p>\n\n\n\n<p>Ribs only 0.31 mm wide cannot allow adhesive to retreat during bonding, causing pure glue to overflow and block the stiffener holes.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><a href=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2025\/12\/555.png\"><img decoding=\"async\" src=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2025\/12\/555.png\" alt=\"Why This Rigid-Flex PCB Was Inherently Difficult?\" class=\"wp-image-18124\"\/><\/a><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Technical_Challenge_1_Thick_Copper_Etching_with_Narrow_Spacing\"><\/span>Technical Challenge #1: Thick Copper Etching with Narrow Spacing<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>A 2 oz <strong>thick copper PCB<\/strong> combined with:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>0.15 mm trace\/space<\/li>\n\n\n\n<li>0.05 mm annular ring<\/li>\n\n\n\n<li>0.66 mm PTH<\/li>\n<\/ul>\n\n\n\n<p>creates a situation where compensation is unavoidable.<\/p>\n\n\n\n<p>However, after compensation (~0.007 mm), the remaining trace width would drop to:<\/p>\n\n\n\n<p><strong>0.08 mm<\/strong> (0.15 \u2013 0.07 mm)<\/p>\n\n\n\n<p>This is below the safe manufacturability range of most <strong>rigid-flex PCB suppliers<\/strong>.<\/p>\n\n\n\n<p><strong>Best Technology&#8217;s solution<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Eliminated compensation on 0.15 mm traces<\/li>\n\n\n\n<li>Implemented fine-tuned etching control<\/li>\n\n\n\n<li>Maintained ~0.10 mm final copper width<\/li>\n\n\n\n<li>Ensured full electrical reliability<\/li>\n<\/ul>\n\n\n\n<p>This is a proven strategy in <strong>advanced rigid-flex PCB manufacturing<\/strong> for thick-copper builds.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Technical_Challenge_2_Annular_Ring_Integrity_in_Plated_Through_Holes\"><\/span>Technical Challenge #2: Annular Ring Integrity in Plated Through Holes<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p>Annular rings &lt;0.10 mm are extremely vulnerable to:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Drill wander<\/li>\n\n\n\n<li>Etching undershoot<\/li>\n\n\n\n<li>Copper thinning<\/li>\n<\/ul>\n\n\n\n<p>This is especially critical in <strong>high-reliability rigid-flex PCBs<\/strong>, where via integrity is essential.<\/p>\n\n\n\n<p><strong>Best Technology&#8217;s solution<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Applied rigid-board-level PTH plating process<\/li>\n\n\n\n<li>Improved copper thickness inside the via barrel<\/li>\n\n\n\n<li>Adjusted drilling control to <strong>0.65 \u00b1 0.075 mm<\/strong><\/li>\n\n\n\n<li>Customer accepted partial ring breakage as long as electrical integrity remained intact<\/li>\n<\/ul>\n\n\n\n<p>This ensured consistent via performance even in ultra-dense rigid-flex PCB layouts.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><a href=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2025\/12\/rigid-flex-pcb-1.png\"><img decoding=\"async\" src=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2025\/12\/rigid-flex-pcb-1.png\" alt=\"rigid flex pcb\" class=\"wp-image-18125\"\/><\/a><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Technical_Challenge_3_Stiffener_Bonding_Alignment_and_Adhesive_Overflow\"><\/span>Technical Challenge #3: Stiffener Bonding, Alignment, and Adhesive Overflow<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p><strong>1. Why stiffener tolerance was problematic<\/strong><\/p>\n\n\n\n<p>In <strong>rigid-flex PCB assembly<\/strong>, stiffeners are critical for mechanical reinforcement. However:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Hole spacing was only 0.60 mm<\/li>\n\n\n\n<li>Stiffener clearance only 0.15 mm per side<\/li>\n\n\n\n<li>Combined tolerance \u00b10.25 mm<\/li>\n<\/ul>\n\n\n\n<p>This inevitably leads to the stiffener covering the pads unless advanced alignment controls are used.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><a href=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2025\/12\/rigid-flex-pcb-stiffener.png\"><img decoding=\"async\" src=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2025\/12\/rigid-flex-pcb-stiffener.png\" alt=\"rigid flex pcb with stiffener\" class=\"wp-image-18126\"\/><\/a><\/figure>\n\n\n\n<p><strong>2. Why glue overflow occurs<\/strong><\/p>\n\n\n\n<p>Thin ribs (0.31 mm) cannot provide an escape path for adhesive. During lamination:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The glue squeezes into the holes<\/li>\n\n\n\n<li>Holes become blocked<\/li>\n\n\n\n<li>Boards fail inspection<\/li>\n<\/ul>\n\n\n\n<p><strong>3. Best Technology\u2019s engineered solution<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Pre-laminated pure adhesive onto FR4 stiffener<\/li>\n\n\n\n<li>Re-drilled stiffener holes after bonding<\/li>\n\n\n\n<li>Greatly reduced glue overflow<\/li>\n\n\n\n<li>Added 100% AOI + manual inspection for hole clearing<\/li>\n\n\n\n<li>Rejected defective boards, shipped only fully passing units<\/li>\n<\/ul>\n\n\n\n<p>This is a common best practice in <strong>flex PCB stiffener processing<\/strong> when tolerances are tight.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"DFM_Guidelines_for_Rigid-Flex_PCB_Designers\"><\/span>DFM Guidelines for Rigid-Flex PCB Designers<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Avoid annular rings under 0.15 mm, especially in 2 oz copper flex-rigid PCB design.<\/li>\n\n\n\n<li>Avoid combining thick copper with fine lines, this will increase manufacturing risk.<\/li>\n\n\n\n<li>Ensure stiffener clearance > total tolerance stack-up. If your clearance is smaller than the alignment tolerance, the stiffener will inevitably shift.<\/li>\n\n\n\n<li>Keep stiffener ribs \u22650.5 mm<\/li>\n\n\n\n<li>Send your design for DFM review before finalizing. A good<a href=\"https:\/\/www.bestfpc.com\/\"> <strong>rigid-flex PCB manufacturer<\/strong><\/a> will help adjust the stack-up, drill size, and stiffener layout to avoid expensive redesigns.<\/li>\n<\/ol>\n\n\n\n<p>This case demonstrates how a complex <strong>rigid-flex PCB<\/strong>\u2014with 2 oz copper, ultra-fine traces, small annular rings, and extreme stiffener constraints\u2014can be successfully manufactured through detailed engineering, advanced process control, and disciplined quality screening.<\/p>\n\n\n\n<p>Best Technology combines strong fabrication capability with practical DFM insight, enabling customers to produce compact, reliable, and manufacturable <strong><a href=\"https:\/\/www.bestfpc.com\/design-guidance\/\">rigid-flex PCB designs<\/a><\/strong> that perform consistently under demanding conditions.<\/p>\n\n\n\n<p>If you need support with your next rigid-flex or flex PCB project, our engineering team is ready to assist with stack-up review, DFM checks, or trial builds.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Recently, Best Technology faced a huge challenge in a 2oz copper rigid flex PCB manufacturing, this board appeared simple on the drawing but revealed multiple layers of engineering challenges once entering mass production. But finally, we finished this project very well and overcome this challenge, let\u2019s see what are the challenges on this project and [&hellip;]<\/p>\n","protected":false},"author":623,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_uf_show_specific_survey":0,"_uf_disable_surveys":false,"footnotes":""},"categories":[175,174,164,3,162],"tags":[842,3196,843,977,986],"class_list":["post-18114","post","type-post","status-publish","format-standard","hentry","category-best-pcb","category-bestpcb","category-design-guide","category-pcb-news","category-rigid-flex-circuit","tag-rigid-flex-pcb-2","tag-rigid-flex-pcb-assembly","tag-rigid-flex-pcb-design","tag-rigid-flex-pcb-manufacturer","tag-rigid-flex-pcb-manufacturing"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.bestpcbs.com\/blog\/wp-json\/wp\/v2\/posts\/18114","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bestpcbs.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bestpcbs.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bestpcbs.com\/blog\/wp-json\/wp\/v2\/users\/623"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bestpcbs.com\/blog\/wp-json\/wp\/v2\/comments?post=18114"}],"version-history":[{"count":2,"href":"https:\/\/www.bestpcbs.com\/blog\/wp-json\/wp\/v2\/posts\/18114\/revisions"}],"predecessor-version":[{"id":18128,"href":"https:\/\/www.bestpcbs.com\/blog\/wp-json\/wp\/v2\/posts\/18114\/revisions\/18128"}],"wp:attachment":[{"href":"https:\/\/www.bestpcbs.com\/blog\/wp-json\/wp\/v2\/media?parent=18114"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bestpcbs.com\/blog\/wp-json\/wp\/v2\/categories?post=18114"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bestpcbs.com\/blog\/wp-json\/wp\/v2\/tags?post=18114"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}