{"id":38482,"date":"2026-11-06T17:35:10","date_gmt":"2026-11-06T09:35:10","guid":{"rendered":"https:\/\/www.bestpcbs.com\/blog\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/"},"modified":"2026-11-06T17:35:10","modified_gmt":"2026-11-06T09:35:10","slug":"ceramic-substrate-cte-copper-pad-cracks","status":"publish","type":"post","link":"https:\/\/www.bestpcbs.com\/blog\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/","title":{"rendered":"Ceramic Substrate CTE: Why Copper Pad Edges Crack"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_89 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\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#What_Does_Ceramic_Substrate_CTE_Mean\" >What Does Ceramic Substrate CTE Mean?<\/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\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#Detailed_CTE_Parameters_for_Bare_Ceramic_Materials\" >Detailed CTE Parameters for Bare Ceramic Materials<\/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\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#Alumina_vs_Aluminum_Nitride_Which_Interface_Matters\" >Alumina vs Aluminum Nitride: Which Interface Matters?<\/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\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#Why_Copper_Edges_Are_More_Vulnerable\" >Why Copper Edges Are More Vulnerable<\/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\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#Worked_Example_A_20_mm_Pad_and_a_100%C2%B0C_Swing\" >Worked Example: A 20 mm Pad and a 100\u00b0C Swing<\/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\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#Why_the_Example_Is_Not_a_Stress_or_Lifetime_Prediction\" >Why the Example Is Not a Stress or Lifetime Prediction<\/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\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#What_Copper_Thickness_and_Pattern_Change\" >What Copper Thickness and Pattern Change<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#When_DBC_and_AMB_Are_Worth_Comparing\" >When DBC and AMB Are Worth Comparing<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#Thermal_Cycling_vs_Power_Cycling\" >Thermal Cycling vs Power Cycling<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#How_to_Compare_Two_Substrates_Fairly\" >How to Compare Two Substrates Fairly<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#What_to_Inspect_After_Cycling\" >What to Inspect After Cycling<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#What_a_Cross-Section_Can_Confirm\" >What a Cross-Section Can Confirm<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#What_to_Send_for_a_Substrate_Review\" >What to Send for a Substrate Review<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-14\" href=\"https:\/\/www.bestpcbs.com\/blog\/2026\/11\/ceramic-substrate-cte-copper-pad-cracks\/#FAQ\" >FAQ<\/a><\/li><\/ul><\/nav><\/div>\n<div class=\"yzp-no-index\"><\/div><p>Copper and ceramic do not expand by the same amount when heated. Bond them together, and they cannot move independently. That mismatch can concentrate stress at the edges of copper pads. Here is how to estimate the mismatch and decide what needs testing before choosing a substrate for a power module.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"What_Does_Ceramic_Substrate_CTE_Mean\"><\/span>What Does Ceramic Substrate CTE Mean?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>CTE is the coefficient of thermal expansion. A value of 5 ppm\/K means a free, uniform piece changes length by about five millionths of its original length for each kelvin of temperature change, within the range where that coefficient applies. A one-kelvin change has the same magnitude as a one-degree Celsius change.<\/p>\n<figure><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2026\/11\/copper-ceramic-top.jpg\" width=\"1120\" height=\"747\" style=\"max-width:100%;height:auto\" alt=\"Patterned copper on a white ceramic power substrate\"><figcaption>AI-generated illustration of a metallized ceramic substrate, not a qualified part.<\/figcaption><\/figure>\n<h2><span class=\"ez-toc-section\" id=\"Detailed_CTE_Parameters_for_Bare_Ceramic_Materials\"><\/span>Detailed CTE Parameters for Bare Ceramic Materials<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The following bare ceramic values come from the <a href=\"https:\/\/www.rogerscorp.com\/advanced-electronics-solutions\/curamik-ceramic-substrates\">Rogers curamik substrate specifications<\/a>. They are material examples over a stated range, not guaranteed properties for every grade or the effective CTE of the finished part.<\/p>\n<figure class=\"wp-block-table\">\n<table>\n<tbody>\n<tr>\n<td><strong>Bare ceramic<\/strong><\/td>\n<td><strong>Linear CTE<\/strong><\/td>\n<td><strong>Stated temperature range<\/strong><\/td>\n<\/tr>\n<tr>\n<td>&#8212;<\/td>\n<td>&#8212;<\/td>\n<td>&#8212;<\/td>\n<\/tr>\n<tr>\n<td>Alumina<\/td>\n<td>6.8 ppm\/K<\/td>\n<td>20\u00b0C to 300\u00b0C<\/td>\n<\/tr>\n<tr>\n<td>Aluminum nitride<\/td>\n<td>4.7 ppm\/K<\/td>\n<td>20\u00b0C to 300\u00b0C<\/td>\n<\/tr>\n<tr>\n<td>Silicon nitride<\/td>\n<td>2.5 ppm\/K<\/td>\n<td>20\u00b0C to 300\u00b0C<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n<h2><span class=\"ez-toc-section\" id=\"Alumina_vs_Aluminum_Nitride_Which_Interface_Matters\"><\/span>Alumina vs Aluminum Nitride: Which Interface Matters?<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<figure class=\"wp-block-table\">\n<table>\n<tbody>\n<tr>\n<td><strong>Review point<\/strong><\/td>\n<td><strong>Alumina example<\/strong><\/td>\n<td><strong>Aluminum nitride example<\/strong><\/td>\n<\/tr>\n<tr>\n<td>&#8212;<\/td>\n<td>&#8212;<\/td>\n<td>&#8212;<\/td>\n<\/tr>\n<tr>\n<td>Free expansion relative to copper<\/td>\n<td>Smaller mismatch in the worked example<\/td>\n<td>Larger mismatch in the worked example<\/td>\n<\/tr>\n<tr>\n<td>Heat transfer through the ceramic<\/td>\n<td>Compare actual grade and thickness<\/td>\n<td>Often chosen for higher conductivity; verify the grade<\/td>\n<\/tr>\n<tr>\n<td>Qualification decision<\/td>\n<td>Compare the full bonded stack<\/td>\n<td>Compare the full bonded stack<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n<p>A ceramic closer to the expansion of copper is not necessarily closer to the expansion of the semiconductor die. Identify which interface is driving the failure before treating any one material property as the selection rule.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"Why_Copper_Edges_Are_More_Vulnerable\"><\/span>Why Copper Edges Are More Vulnerable<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Away from a pad edge, the joined layers constrain each other. At the edge of the metal, that constraint changes abruptly. <a href=\"https:\/\/www.rogerscorp.com\/blog\/2018\/reliability-of-metallized-ceramic-substrates-for-power-electronics-applications\">Rogers&#8217; reliability discussion<\/a> identifies pad edges and corners as stress concentration sites. A crack near the edge still needs failure analysis to rule out other causes.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"Worked_Example_A_20_mm_Pad_and_a_100%C2%B0C_Swing\"><\/span>Worked Example: A 20 mm Pad and a 100\u00b0C Swing<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>For an illustrative uniform temperature rise from 25\u00b0C to 125\u00b0C, assume copper CTE is 17 ppm\/K and use the data sheet&#8217;s average alumina value of 6.8 ppm\/K as an approximation. The difference in free length change is 20 mm \u00d7 (17 \u2212 6.8) \u00d7 0.000001\/K \u00d7 100 K, or about 0.0204 mm. Using the listed aluminum nitride value gives about 0.0246 mm instead.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"Why_the_Example_Is_Not_a_Stress_or_Lifetime_Prediction\"><\/span>Why the Example Is Not a Stress or Lifetime Prediction<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>The calculated values compare two unbonded materials that would otherwise expand freely. They are not actual slip, crack opening, or deformation of the bonded part. Stress also depends on elastic and plastic behavior, geometry, temperature gradients, residual stress and restraint from the rest of the assembly.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"What_Copper_Thickness_and_Pattern_Change\"><\/span>What Copper Thickness and Pattern Change<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Copper thickness and pad shape change the mechanical load carried by the ceramic. Corners, pad spacing and differences between the top and bottom patterns can influence the result. Ask the supplier to review the exact pattern rather than transferring rules from a different ceramic or joining process.<\/p>\n<figure><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/www.bestpcbs.com\/blog\/wp-content\/uploads\/2026\/11\/ceramic-edge.jpg\" width=\"1120\" height=\"560\" style=\"max-width:100%;height:auto\" alt=\"Side view of copper bonded to a white ceramic coupon\"><figcaption>AI-generated illustration of a copper\u2013ceramic interface, not a measured section.<\/figcaption><\/figure>\n<h2><span class=\"ez-toc-section\" id=\"When_DBC_and_AMB_Are_Worth_Comparing\"><\/span>When DBC and AMB Are Worth Comparing<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Direct bonded copper (DBC) and active metal brazing (AMB) are different ways to join metal and ceramic. Compare the actual ceramic grade, bond structure, copper thickness and intended duty. A cycle count for one construction does not establish a cycle count for all substrates made with the same bonding method.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"Thermal_Cycling_vs_Power_Cycling\"><\/span>Thermal Cycling vs Power Cycling<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>A chamber test changes the ambient temperature around the specimen. A power cycling test changes the load in a powered device and can create different temperature gradients. Select a test based on where the real assembly heats and what failure mode you need to investigate.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"How_to_Compare_Two_Substrates_Fairly\"><\/span>How to Compare Two Substrates Fairly<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Keep the pad geometry, attachment and inspection criteria consistent where possible. Record temperature limits, ramp rates, dwell times, sample sizes and inspection intervals. If you deliberately change copper thickness or another factor, record it as a variable rather than attributing every result to the ceramic.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"What_to_Inspect_After_Cycling\"><\/span>What to Inspect After Cycling<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Use the before-test condition as a baseline. Inspect representative copper corners and edges, and document the location and direction of any damage. Define whether the test is looking for ceramic cracking, bond separation, solder fatigue or an electrical change; these findings are not interchangeable.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"What_a_Cross-Section_Can_Confirm\"><\/span>What a Cross-Section Can Confirm<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>A section through the suspect edge can show whether a crack runs into the ceramic or whether separation follows an interface. Take a comparison section away from the damaged area if the inspection plan allows. Use those observations with the test history rather than assigning a failure mechanism from a surface photo alone.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"What_to_Send_for_a_Substrate_Review\"><\/span>What to Send for a Substrate Review<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Send the ceramic grade, metal thicknesses, pad artwork, attachment method, temperature history and intended inspection criteria. For related construction information, see the <a href=\"https:\/\/www.bestpcbs.com\/products\/ceramic-substrate.htm\">DCB ceramic design guide<\/a>. Contact Best Technology at <a href=\"mailto:sales@bestpcbs.com\">sales@bestpcbs.com<\/a> to discuss the design requirements.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"FAQ\"><\/span>FAQ<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<h3>Does aluminum nitride always last longer than alumina?<\/h3>\n<p>No. Thermal conductivity and thermal cycling life answer different questions. A material that lowers the operating temperature may still behave differently at a copper edge or a solder joint. Compare substrates with representative geometry and attachment under a duty cycle relevant to your application before drawing a reliability conclusion.<\/p>\n<h3>Why do cracks start near the copper corner?<\/h3>\n<p>The copper ends at the edge, but the ceramic continues. The change in restraint concentrates stress near that boundary, particularly at corners. Location alone is not proof of a thermal expansion failure; compare inspection records, cross-sections and handling history before assigning a root cause.<\/p>\n<h3>Is the bare ceramic CTE the finished substrate CTE?<\/h3>\n<p>No. A metallized substrate combines materials with different expansion behavior, and the effective response depends on the construction. Use the bare ceramic value for material comparisons and early estimates. Ask for an appropriate measured or modeled property when the overall movement of the finished structure matters.<\/p>\n<h3>Can I calculate lifetime from the CTE difference?<\/h3>\n<p>No. The CTE difference gives a first estimate of how differently the free materials would move. It does not capture bonding, plastic deformation, fracture behavior or the true temperature field. Use modeling and testing to compare designs, and do not translate chamber cycles directly into field years without a validated model.<\/p>\n<h3>Should I make all copper pads smaller?<\/h3>\n<p>Not as a blanket rule. A smaller pad can change stress distribution, but it can also affect current flow, heat spreading, electrical clearances and assembly. Evaluate alternatives together with the supplier and test the resulting geometry rather than applying a universal size limit to different constructions.<\/p>\n<h3>What if only one side has a large copper area?<\/h3>\n<p>An uneven metal pattern can change how the substrate bends during heating and cooling. Include both sides in the design review rather than describing only the visible top pattern. Confirm the required flatness and check it under relevant conditions if warpage would affect attachment or assembly.<\/p>\n<h3>Can I use a chamber test instead of power cycling?<\/h3>\n<p>A chamber test is useful for a comparative evaluation, but it does not reproduce every gradient created by a powered die. Choose the test based on the suspected failure mechanism. A useful plan may use both methods if ambient cycling and local heating each matter in service.<\/p>\n<h3>Which drawings and data should I ask the supplier for?<\/h3>\n<p>Request the ceramic grade, thickness, copper pattern on both faces, joining method and documented test conditions for any reliability data. If the supplier shares cycle results, check whether the tested geometry and inspection criteria apply to your design before using those numbers as acceptance evidence.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Learn why copper pad edges can crack on ceramic substrates, estimate thermal expansion mismatch, and plan a thermal cycling comparison for power modules.<\/p>\n","protected":false},"author":32827,"featured_media":38480,"comment_status":"open","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_uf_show_specific_survey":0,"_uf_disable_surveys":false,"footnotes":""},"categories":[174],"tags":[9119,9120,9122,9121],"class_list":["post-38482","post","type-post","status-publish","format-standard","hentry","category-bestpcb","tag-ceramic-substrate-cte","tag-copper-ceramic-mismatch","tag-power-module-reliability","tag-thermal-cycling"],"acf":[],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 5.0.4 - aioseo.com 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