{"id":11405,"date":"2025-08-13T15:22:06","date_gmt":"2025-08-13T19:22:06","guid":{"rendered":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/?p=11405"},"modified":"2026-03-27T09:47:34","modified_gmt":"2026-03-27T13:47:34","slug":"copper-thickness","status":"publish","type":"post","link":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/2025\/08\/13\/copper-thickness\/","title":{"rendered":"Copper thickness: Closing the knowledge gap to design success"},"content":{"rendered":"\n

I\u2019m occasionally asked why 0.6 mils (15 \u03bcm) is often used to for thickness of half-ounce copper rather than 0.7 mils (18 \u03bcm) and similarly why 1.2 mils (30 \u03bcm) is often used for 1-oz. copper instead of 1.4 mils (36 \u03bcm).  If you\u2019re curious about the details or if none of these numbers are familiar to you, here\u2019s a quick primer on the subject.  The copper thickness parameter, \u201ct,\u201d in FIGURE 1<\/em> shows the thickness we\u2019re interested in here.<\/p>\n\n\n

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\"image
FIGURE 1. The parameter \u201ct,\u201d shown in a stripline cross section, represents the copper thickness we\u2019re interested in here. (Image from Z-zero\u2019s Z-solver software.)<\/figcaption><\/figure><\/div>\n\n\n

Copper weight\u2014why we use ounces<\/h3>\n\n\n\n

Let\u2019s start the discussion with why weights (ounces) are used to describe thickness.<\/p>\n\n\n\n

If someone asked your height and you told them 180 pounds, they\u2019d think you were crazy.  However, in electronics, weight is still used as a determinant for copper thickness.  Why is that? <\/p>\n\n\n\n

The ounce rating has its roots in the gold-foil industry and subsequently for copper\u2019s use in the building industry. It\u2019s based on spreading an ounce of a given metal over one square foot of area.  Today\u2019s copper foils for printed-circuit boards are manufactured and sold by weight. The method has persisted in its use for electronic circuits and there\u2019s a good reason for it.<\/p>\n\n\n\n

Nominal thickness<\/h3>\n\n\n\n

Thickness determination of rolled and electro-deposited (ED) copper foil by weight provides far more accuracy than contact-thickness gauges. Since the topography of treated foil varies greatly, and since the density of copper is known, weighing a 1-by-1 foot sheet is the best way to determine the average thickness of a sheet of copper.  So formally, the unit that we refer to as \u201counces\u201d is actually ounces per square foot<\/em>.  For example, 1-oz. copper weighs one ounce per square foot and is 0.00135 inches or 34 \u03bcm thick, nominally, as shown in TABLE 1<\/em>.  Some sources report the nominal thickness of 1-oz. copper at 35 \u03bcm, but I\u2019m working off of the IPC numbers here rather than Wikipedia.<\/p>\n\n\n\n

Copper Weight (oz.)<\/strong><\/td>Nominal Thickness<\/strong><\/td>After Fabrication<\/strong><\/td>90% of Nominal<\/strong><\/td><\/tr>
1\/2 oz.<\/td>0.68 mils (17.1 \u03bcm)<\/td>0.6 mils (15 \u03bcm)<\/td>0.61 mils (15.5 \u03bcm)<\/td><\/tr>
1 oz.<\/td>1.35 mils (34.3 \u03bcm)<\/td>1.2 mils (30 \u03bcm)<\/td>1.22 mils (30.9 \u03bcm)<\/td><\/tr>
2 oz.<\/td>2.7 mils (68.6 \u03bcm)<\/td>2.4 mils (61 \u03bcm)<\/td>2.43 mils (61.7 \u03bcm)<\/td><\/tr><\/tbody><\/table>
TABLE 1.  Copper foils are available in several thicknesses, measured by weight.  The most common copper thicknesses used in multilayer PCBs are shown here, including nominal thicknesses, per IPC-4562A.<\/figcaption><\/figure>\n\n\n\n
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Go beyond copper thickness.<\/strong><\/h2>\n\n\n\n

Explore the relationship between copper roughness and signal integrity. Discover 10 critical things you need to know about copper roughness and its impact on board costs during your stackup design process. <\/p>\n\n\n\n

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View webinar<\/a><\/div>\n<\/div>\n<\/div>
\"copper<\/a><\/figure><\/div>\n\n\n\n<\/div>\n\n\n\n

IPC-4562A<\/h3>\n\n\n\n

You may read other values for these nominal copper thicknesses from other sources, but the manufacturers in the PCB industry are working from IPC-4562A, the \u201cMetal Foil for Printed Board Applications\u201d standard.  If your laminate or copper vendor is providing you with different thicknesses, you may want to use this standard\u2014or this article\u2014as a guide for double-checking the numbers they\u2019re providing.  To this day, in fact, I see electronic design (EDA) tools using nominal copper thicknesses<\/a> in their stackup representations rather than the as-fabricated thicknesses.<\/p>\n\n\n\n

The subject of copper thickness and weight becomes even more interesting when you factor in the  tolerances<\/em><\/strong> described in IPC-4562A<\/a>, which specifies that the minimum thickness<\/em> shall not be below the nominal value in TABLE 1<\/em> by more than 10 percent.  If you\u2019re a copper manufacturer pushing 2,000-5,000 tons of copper foil out per month and you can keep your volume-production copper weights above 90 percent of the nominal values in TABLE 1<\/em>, that\u2019s a great way to save some money and that\u2019s in fact what happens in practice.  The third column in TABLE 1<\/em> shows these 90 percent of nominal values, which are shown graphically for one-ounce copper in FIGURE 2<\/em>.<\/p>\n\n\n\n

\"the
FIGURE 2. The variation in copper-foil thickness for 1-ounce copper, including the thickness that many designers assume, the IPC-4562A nominal thickness, the minimum IPC tolerance thickness, and a typical value after fabrication.<\/figcaption><\/figure>\n\n\n\n

After fabrication<\/h3>\n\n\n\n

After fabrication, including the etching and cleaning processes, the final thickness of these foils will average 0.2 mils (5 microns) thinner than the \u201cassumed\u201d copper thickness (1.4 mils) for one-ounce copper, as shown in FIGURE 2.  TABLE 1<\/em> shows that half-ounce copper will have a final thickness of about 0.6 mils (15 \u03bcm). Your fabricator may have an etching process that differs slightly from these values, but on 95 percent of the stackups I see from fabricators, these are the values they use.<\/p>\n\n\n\n

As a side note for comparison, the aluminum foil that most people use for household cooking purposes is about 0.6 mils (15 \u03bcm) thick, just like half-ounce copper.<\/p>\n\n\n\n

Consequences of using inaccurate copper thicknesses<\/h3>\n\n\n\n

If you\u2019re looking to calculate bulk resistivity from sheet resistance, sheet thickness is in the denominator and whether you\u2019re getting the copper thickness from an assumed or estimated thickness as opposed to the weight-based methodology noted above, you need to have an understanding of the real values in printed-circuit boards rather than values you might find on Wikipedia, for example.<\/p>\n\n\n\n

I often see engineers, designers and EDA tools rounding the above nominal values to 0.7 mils (18 \u03bcm), 1.4 mils (36 \u03bcm), and 2.8 mils (71 \u03bcm). I\u2019m not normally against rounding, but when you\u2019re rounding in the wrong direction, it needs to be questioned.<\/p>\n\n\n\n

Board thickness, too, will be affected.  On a four-layer design, the difference may not be significant, but on a 20-layer design using one-ounce copper throughout and the wrong assumptions, your board thickness will be off by as much as 4 mils.  I\u2019m pretty sure the mechanical engineers, if no one else, would appreciate it if PCB designers worked with a sharper pencil. FIGURE 3 shows impedance and skin effect loss at 10 GHz for an 85-ohm example cross section for half-ounce copper using the post-fabrication number.<\/p>\n\n\n\n

\"FIGURE
FIGURE 3. Impedance and skin effect loss at 10 GHz for an 85-ohm example stripline cross section from Figure 1 using half-ounce copper and the post-fabrication number. (Image from Z-planner Enterprise.)<\/figcaption><\/figure>\n\n\n\n

Conclusion<\/h3>\n\n\n\n

Truth be told, the difference between using a 0.7 mil copper thickness and the more-correct 0.6 mil thickness isn\u2019t huge, but if you\u2019re tracking millivolts and picoseconds while signaling at multi-gigabit SERDES speeds and taking the time to simulate virtual prototypes using expensive signal-integrity software, it only makes sense to take every form of avoidable uncertainty off the table.  Differential impedance will be affected.  Signal integrity and crosstalk simulations will be affected.  And losses from skin effect will be affected at some level.  Why not feed that expensive SI simulator real numbers?<\/p>\n\n\n\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

Copper thickness determination of rolled and electro-deposited (ED) copper foil by weight provides far more accuracy than contact-thickness gauges. Since the topography of treated foil varies greatly, and since the density of copper is known, weighing a 1-by-1 foot sheet is the best way to determine the average thickness of a sheet of copper. \u00a0So formally, the unit that we refer to as \u201counces\u201d is actually ounces per square foot. <\/p>\n","protected":false},"author":115516,"featured_media":11445,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"spanish_translation":"","french_translation":"","german_translation":"","italian_translation":"","polish_translation":"","japanese_translation":"","chinese_translation":"","footnotes":""},"categories":[17],"tags":[1730,1125],"industry":[341],"product":[998],"coauthors":[2051],"class_list":["post-11405","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-tips-tricks","tag-pcb-design-best-practices","tag-stackup","industry-electronics-semiconductors","product-z-planner-enterprise"],"featured_image_url":"https:\/\/blogs.sw.siemens.com\/wp-content\/uploads\/sites\/65\/2025\/06\/IMG_1699.jpeg","_links":{"self":[{"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/posts\/11405","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/users\/115516"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/comments?post=11405"}],"version-history":[{"count":4,"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/posts\/11405\/revisions"}],"predecessor-version":[{"id":11529,"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/posts\/11405\/revisions\/11529"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/media\/11445"}],"wp:attachment":[{"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/media?parent=11405"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/categories?post=11405"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/tags?post=11405"},{"taxonomy":"industry","embeddable":true,"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/industry?post=11405"},{"taxonomy":"product","embeddable":true,"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/product?post=11405"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/blogs.sw.siemens.com\/electronic-systems-design\/wp-json\/wp\/v2\/coauthors?post=11405"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}