{"id":202,"date":"2018-03-31T01:12:45","date_gmt":"2018-03-31T01:12:45","guid":{"rendered":"https:\/\/ninedotconnectssandbox.com\/blog\/?p=202"},"modified":"2020-08-29T18:08:49","modified_gmt":"2020-08-29T18:08:49","slug":"detangling-a-power-short","status":"publish","type":"post","link":"https:\/\/ninedotconnectssandbox.com\/blog\/index.php\/2018\/03\/31\/detangling-a-power-short\/","title":{"rendered":"Detangling a Power Short"},"content":{"rendered":"

Preface:\u00a0 Mark Saunders is currently a senior at the Rochester Institute of Technology.\u00a0 He is one of the few undergraduate students with a working knowledge of PCB design.\u00a0 Although his focus is firmware, he has used Altium Designer for several personal and class projects.<\/em><\/p>\n

<\/p>\n

I met Mark and his family through my daughter\u2019s attendance at the same grade school.\u00a0 While in high school, he obtained a student license for Altium Designer with my assistance.\u00a0 Mark and I have kept in contact throughout the years.<\/em><\/p>\n

\"\"<\/p>\n

The Far Out Rocket Team.\u00a0 Mark Saunders is in the back row, second from the right.<\/em><\/p>\n

Mark\u2019s intern experience includes SpaceX where he met several other sharp individuals from various North American colleges and universities in different engineering disciplines.\u00a0 These interns decided to create the Far Out Rocketry team for the FAR-MARS launch contest.\u00a0 This is no easy feat since the team members are geographically separated.\u00a0 Mark\u2019s role is a custom flight computer board design.<\/em><\/p>\n

The adventure began at 9:00 PM PST on March 12th.\u00a0 In true engineering college fashion, Mark was up at midnight (EST) burning the candle at both ends.\u00a0 He called me, seeking guidance regarding a power short on his flight computer board.\u00a0 Three four-layer boards were made, one was populated.\u00a0 Power shorts were discovered on each board!<\/p>\n

The problem with power shorts is they can be very difficult to track down.\u00a0 For the next hour, we discussed the issue and used GoToMeeting to look at the PCB layout together.\u00a0 There were no glaring violations, though I did think it was unusual that copper clearances were 5 mils.\u00a0 This tends to be at the cutting edge of price-sensitive fabricators.\u00a0 I asked about the fabricator but did not probe deep enough.\u00a0 This later became apparent.<\/p>\n

What\u2019s one to do?\u00a0 One suggestion that came from the rocket team was to crank up the voltage and see if there were any hot spots.\u00a0 Unfortunately, Mark did not have temperature sensing equipment available.\u00a0 He had a diamond bandsaw available at the time, so I suggested a binary search to cut the board down to where he could isolate the short through a diode check.<\/p>\n

After the call was completed, my wife (also an engineer in the field of ICs) suggested there may be more than one power short.\u00a0 Sure enough, the next day Mark sent the picture below, confirming my wife\u2019s suspicion:<\/p>\n

\"\"<\/p>\n

In further e-mail communications, Mark had discovered that the other board not only had similar shorts but also additional shorts.\u00a0 This made it clear that it was a fabrication issue.<\/p>\n

In further discussions, I learned this fabricator had a student sponsorship program.\u00a0 If the layer stackup matches and panel real estate is available, the idea is to piggyback the student\u2019s design onto a panel being run for a customer.\u00a0 These panels are usually 24″ X 18″, with approximately 1 inch of the panel edge being kept cleared for mounting equipment.\u00a0 Mark\u2019s design was more than likely placed on the periphery of the panel.\u00a0 The center of the panel real estate is reserved for the company paying the standard rate for the fabrication.<\/p>\n

Having a board fabricated on the periphery can be an issue due to possible misregistration between layers.\u00a0 The center is least impacted by such issues but misregistration nearing the edges can be more pronounced.<\/p>\n

\"\"<\/p>\n

The secret of most fabricators is a customer\u2019s design will be reviewed and modified by a CAM technician.\u00a0 They will clean up potential copper issues to ensure higher yield.\u00a0 However, one needs to understand that the customer\u2019s design documentation and the fabricator\u2019s documentation when the product is finished are not the same.\u00a0 This is why boards that work with a prototyping fabricator may not work with a fabricator in the business of \u201cas is\u201d mass production.\u00a0 Most fabricators will NOT disclose their work done on the board and most customers do not know their designs were modified.<\/p>\n

While CAM service is provided to commercial customers, it is not likely provided to student projects.\u00a0 Also, Mark used the ruleset from the fabricator allowing 5 mils copper clearance.\u00a0 This clearance may have worked if a CAM technician cleaned up the board and the board was being placed in the center of the panel.\u00a0 In the redesign, Mark made the clearances more robust at 10 mils.\u00a0 The fabricator was very accommodating, allowing Mark another run of the board, this time with success.<\/p>\n

There were lessons learned that go beyond an EDA tool.\u00a0 In the end, PCB designers must not only know the tools they are using to design the board but the fabrication process as well.<\/p>\n

———————-<\/p>\n

We at Nine Dot Connects understand that these are good lessons to learn in an undergraduate environment.\u00a0 However, they are not fun to learn in a work environment, where budget constraints and market windows (and career advancement) are on the line.\u00a0 That is why we created the PCB Foundations<\/em><\/a> training.\u00a0 This three-day course is designed to walk you through the entire design process, conception through production, helping you become aware of the little things that make a big difference when manufacturing a board.<\/p>\n

Authored by Paul Taubman<\/p>\n

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

Preface:\u00a0 Mark Saunders is currently a senior at the Rochester Institute of Technology.\u00a0 He is one of the few undergraduate students with a working knowledge of PCB design.\u00a0 Although his focus is firmware, he has used Altium Designer for several personal and class projects.<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[99,28,95,98,97,32,55,93,96,94],"class_list":["post-202","post","type-post","status-publish","format-standard","hentry","category-9dot-thinking","tag-cam","tag-eda","tag-far-mars","tag-flight-computer","tag-launch","tag-pcb","tag-pcb-foundations","tag-power-short","tag-rocket","tag-spacex"],"_links":{"self":[{"href":"https:\/\/ninedotconnectssandbox.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/202","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ninedotconnectssandbox.com\/blog\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ninedotconnectssandbox.com\/blog\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ninedotconnectssandbox.com\/blog\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/ninedotconnectssandbox.com\/blog\/index.php\/wp-json\/wp\/v2\/comments?post=202"}],"version-history":[{"count":5,"href":"https:\/\/ninedotconnectssandbox.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/202\/revisions"}],"predecessor-version":[{"id":465,"href":"https:\/\/ninedotconnectssandbox.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/202\/revisions\/465"}],"wp:attachment":[{"href":"https:\/\/ninedotconnectssandbox.com\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=202"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ninedotconnectssandbox.com\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=202"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ninedotconnectssandbox.com\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=202"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}