{"id":432,"date":"2015-10-11T15:57:21","date_gmt":"2015-10-11T22:57:21","guid":{"rendered":"http:\/\/pididu.com\/wordpress\/solarbike\/?p=432"},"modified":"2015-10-11T15:57:21","modified_gmt":"2015-10-11T22:57:21","slug":"check-footprints-before-pcb-layout","status":"publish","type":"post","link":"http:\/\/pididu.com\/wordpress\/solarbike\/check-footprints-before-pcb-layout\/","title":{"rendered":"Check Footprints Before PCB Layout"},"content":{"rendered":"<p>I&#8217;m taking some time off from layout to check part footprints (aka land patterns).<\/p>\n<p>Silly me, I thought earlier that checking the footprints would be a simple formality. When I worked at a corporation as an engineer, the CAD components were always made by someone else, usually with a footprint approved by Corporate Engineering. But in this hobby design, I&#8217;m finding that almost every footprint has some imperfection, and that when footprints are adjusted, the layout needs to be adjusted slightly, too.<\/p>\n<p>Important note to self: Be sure to check all footprints BEFORE starting PCB layout.<\/p>\n<p>Below is one of the footprints that had a critical weakness.<\/p>\n<figure id=\"attachment_434\" aria-describedby=\"caption-attachment-434\" style=\"width: 315px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/pididu.com\/wordpress\/solarbike\/files\/2015\/10\/soic.gif\"><img decoding=\"async\" loading=\"lazy\" class=\"size-full wp-image-434\" alt=\"soic-8 footprint\" src=\"http:\/\/pididu.com\/wordpress\/solarbike\/files\/2015\/10\/soic.gif\" width=\"315\" height=\"185\" \/><\/a><figcaption id=\"caption-attachment-434\" class=\"wp-caption-text\">When I made the digital component for the ACS723 current sensor, I chose the default SOIC-8 footprint, as that was the package style that the chip came in. It fits, and would be fine for an op-amp or other low-power chip.<\/figcaption><\/figure>\n<figure id=\"attachment_433\" aria-describedby=\"caption-attachment-433\" style=\"width: 297px\" class=\"wp-caption aligncenter\"><a href=\"http:\/\/pididu.com\/wordpress\/solarbike\/files\/2015\/10\/sol.gif\"><img decoding=\"async\" loading=\"lazy\" class=\"size-full wp-image-433\" alt=\"so-8 long footprint\" src=\"http:\/\/pididu.com\/wordpress\/solarbike\/files\/2015\/10\/sol.gif\" width=\"297\" height=\"190\" \/><\/a><figcaption id=\"caption-attachment-433\" class=\"wp-caption-text\">This was the footprint for the MIC4452 MOSFET driver chip. It has a lot more contact area with the high-current pins of the IC. I changed the ACS723 component to use this footprint.<\/figcaption><\/figure>\n<p>While I was doing layout, I noticed that I was continually adjusting the 1206 footprint components by a few mils off the 5-mil layout grid.  The default 1206 footprint in DesignSpark is two 63-mil square pads, with a center-to-center spacing of 134 mils.  Possibly the part was translated from the metric, where 3.2 mm x 1.6 mm were the controlling dimensions.  I adjusted this footprint to be two 70-mil square pads, spaced 140 mils center-to-center.  This should make layout on the 5-mil grid much easier.  I also adjusted the 1210 footprint in similar fashion.  These changes threw off the existing routing for an awful lot of traces by a mil or two in various directions, and a lot of adjustment will be needed.  I&#8217;m not going to fix up the layout just yet, because I&#8217;m still checking the footprints of the rest of components.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I&#8217;m taking some time off from layout to check part footprints (aka land patterns). Silly me, I thought earlier that checking the footprints would be a simple formality. When I worked at a corporation as an engineer, the CAD components were always made by someone else, usually with a footprint approved by Corporate Engineering. But &hellip; <a href=\"http:\/\/pididu.com\/wordpress\/solarbike\/check-footprints-before-pcb-layout\/\" class=\"more-link\">Continue reading <span class=\"screen-reader-text\">Check Footprints Before PCB Layout<\/span> <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[63],"tags":[67,65,66,68],"_links":{"self":[{"href":"http:\/\/pididu.com\/wordpress\/solarbike\/wp-json\/wp\/v2\/posts\/432"}],"collection":[{"href":"http:\/\/pididu.com\/wordpress\/solarbike\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/pididu.com\/wordpress\/solarbike\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/pididu.com\/wordpress\/solarbike\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/pididu.com\/wordpress\/solarbike\/wp-json\/wp\/v2\/comments?post=432"}],"version-history":[{"count":0,"href":"http:\/\/pididu.com\/wordpress\/solarbike\/wp-json\/wp\/v2\/posts\/432\/revisions"}],"wp:attachment":[{"href":"http:\/\/pididu.com\/wordpress\/solarbike\/wp-json\/wp\/v2\/media?parent=432"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/pididu.com\/wordpress\/solarbike\/wp-json\/wp\/v2\/categories?post=432"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/pididu.com\/wordpress\/solarbike\/wp-json\/wp\/v2\/tags?post=432"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}