Every now and again, you get asked about a part that’s been around for ages.\u00a0 There’s not usually any surprises left and any ‘gotchas’ are usually well documented in the datasheet.\u00a0 So when I got a question via one of our catalogue customers about an industry standard\u00a0voltage monitor chip behaving erratically, it came as a bit of a surprise.<\/p>\n
The problem came, they explained, when their end-customer potted their PCB\u00a0containing\u00a0the device with a potting compound, an epoxy resin\u00a0for which\u00a0they kindly provided me with the data sheet.\u00a0 According to their data sheet, the epoxy was suitable for potting transformers and other electronic components.<\/p>\n
I did some reading up on potting compounds and from this research a likely cause of the customer’s issue began to emerge.\u00a0 The problem with epoxy resins is that the glass transition temperature (Tg\u00a0 – the temperature at which the resin goes from being\u00a0soft to being hard)\u00a0is relatively high.<\/p>\n
The Coefficient of Thermal Expansion (CTE) of the potting compounds is higher than that of the\u00a0board, so\u00a0the potting shrinks more than the board as it cools.\u00a0 For through-hole boards this is not a problem as the component leads provide\u00a0‘strain relief’ to alleviate this mismatch in CTE.\u00a0<\/p>\n
However, with surface mount boards,\u00a0as the ambient temperature is below the Tg of the potting compound, the compound becomes harder and pushes against the surface mount component until in some cases it breaks the solder connection.\u00a0 For this reason, epoxy resin is not recommended for surface mount boards.<\/p>\n
For potting surface mount boards, low Tg potting compounds like silicone and urethane,\u00a0which remain flexible and deform rather than moving the component, are recommended.\u00a0 Our customer also supplied a silicone resin for potting via their catalogue and a quick check of the data sheet showed it was recommended for potting surface mount boards.<\/p>\n
Their end customer hasn’t come back with any more questions, so I presume that this was the problem and that the proposed solution is working just fine.<\/p>\n","protected":false},"excerpt":{"rendered":"
Every now and again, you get asked about a part that’s been around for ages.\u00a0 There’s not usually any surprises left and any ‘gotchas’ are usually well documented in the datasheet.\u00a0 So when I got a question via one of our catalogue customers about an industry standard\u00a0voltage monitor chip behaving erratically, it came as a … Continue reading “Potting Problems”<\/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":[1],"tags":[],"class_list":["post-7","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"http:\/\/blog.mtfwalker.com\/index.php?rest_route=\/wp\/v2\/posts\/7","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/blog.mtfwalker.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/blog.mtfwalker.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/blog.mtfwalker.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/blog.mtfwalker.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=7"}],"version-history":[{"count":1,"href":"http:\/\/blog.mtfwalker.com\/index.php?rest_route=\/wp\/v2\/posts\/7\/revisions"}],"predecessor-version":[{"id":8,"href":"http:\/\/blog.mtfwalker.com\/index.php?rest_route=\/wp\/v2\/posts\/7\/revisions\/8"}],"wp:attachment":[{"href":"http:\/\/blog.mtfwalker.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=7"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/blog.mtfwalker.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=7"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/blog.mtfwalker.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=7"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}