RE: PCB coating questions
Arjen - Check the Conditions of Acceptability on the coatings you're interested in using. UL Recognized conformal coatings are, for the most part, are tested for use on the bare board (base laminate) and are not tested for use on solder masks. Regards, Peter L. Tarver Nortel Networks ptar...@nortelnetworks.com -Original Message- From: pe...@itl.co.il [SMTP:pe...@itl.co.il] Sent: Sunday, March 07, 1999 9:38 AM Dear Arjen, Solder mask is not considered as a conformal coating. You may find UL Recognized conformal coating manufacturers in the UL Recognized Component Directory under Coatings for Printed Wiring Boards. To be able to use it on your boards, you must obtain a copy of the UL Conditions of Acceptability (COAs) to ensure that the coating is suitable for the ANSI grade (FR4, etc.) of the board base material. For ITE (UL1950/CSA C22.2 950), you can use a UL Recognized conformal coating or alternatively must subject the the PWB with coating to all the applicable construction and tests in UL1950/CSA C22.2 950 for coated PWBs. For ITE built for Europe, a US/Canadian Recognized/Certified coating is usually not acceptable and the PWB with coating must be subjected to all applicable tests in EN 60950 for coated PWBs. Best Regards, From: Arjen Dragt adr...@inverpower.com Date sent:Thu, 4 Mar 1999 14:59:16 -0500 In looking at meeting CSA and UL spacing requirements for some of our PCB's (in power supplies up to 600 V) some questions concerning the use of conformal coatings (allowing reduction of spacing) have come up. The information that I am seeking is for both CSA and UL; the wording that they use concerning coatings on boards is similar, but not the same. Coatings on a PCB could include both a solder mask, and a strict conformal coating. Does anybody have real-world knowledge as to whether or not a solder mask is accepted by UL/CSA as a coating, and if so, under what conditions? Also, the method by which a coating is applied to a board could have considerable impact on the effectiveness of that coating. For instance, spraying a board will not get at any traces that are buried underneath components, whereas dipping will have a better chance of accessing those hidden areas. The standards that I am looking at say nothing about method of applying a coating (the process). I assume that the decision as to how a coating will be applied is left up to the manufacturer and board supplier. Does anybody out there have best practices that are worth considering when looking at our options for coating methods? Arjen Dragt PETER S. MERGUERIAN I.T.L. (PRODUCT TESTING) LTD. - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
Re: PCB coating questions
Dear Arjen, Solder mask is not considered as a conformal coating. You may find UL Recognized conformal coating manufacturers in the UL Recognized Component Directory under Coatings for Printed Wiring Boards. To be able to use it on your boards, you must obtain a copy of the UL Conditions of Acceptability (COAs) to ensure that the coating is suitable for the ANSI grade (FR4, etc.) of the board base material. For ITE (UL1950/CSA C22.2 950), you can use a UL Recognized conformal coating or alternatively must subject the the PWB with coating to all the applicable construction and tests in UL1950/CSA C22.2 950 for coated PWBs. For ITE built for Europe, a US/Canadian Recognized/Certified coating is usually not acceptable and the PWB with coating must be subjected to all applicable tests in EN 60950 for coated PWBs. Best Regards, From: Arjen Dragt adr...@inverpower.com To: EMC-PSTC Listserv emc-p...@majordomo.ieee.org Subject:PCB coating questions Date sent: Thu, 4 Mar 1999 14:59:16 -0500 Send reply to: Arjen Dragt adr...@inverpower.com In looking at meeting CSA and UL spacing requirements for some of our PCB's (in power supplies up to 600 V) some questions concerning the use of conformal coatings (allowing reduction of spacing) have come up. The information that I am seeking is for both CSA and UL; the wording that they use concerning coatings on boards is similar, but not the same. Coatings on a PCB could include both a solder mask, and a strict conformal coating. Does anybody have real-world knowledge as to whether or not a solder mask is accepted by UL/CSA as a coating, and if so, under what conditions? Also, the method by which a coating is applied to a board could have considerable impact on the effectiveness of that coating. For instance, spraying a board will not get at any traces that are buried underneath components, whereas dipping will have a better chance of accessing those hidden areas. The standards that I am looking at say nothing about method of applying a coating (the process). I assume that the decision as to how a coating will be applied is left up to the manufacturer and board supplier. Does anybody out there have best practices that are worth considering when looking at our options for coating methods? Arjen Dragt PETER S. MERGUERIAN MANAGING DIRECTOR PRODUCT TESTING DIVISION I.T.L. (PRODUCT TESTING) LTD. HACHAROSHET 26, P.O.B. 211 OR YEHUDA 60251, ISRAEL TEL: 972-3-5339022 FAX: 972-3-5339019 E-MAIL: pe...@itl.co.il Visit our Website: http://www.itl.co.il - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
RE: PCB coating questions
Arjen, For insulation over PCB traces, some types of dry film solder mask might be suitable. These films are manufactured to a consistent thickness, and then laminated to the PCB. You need to check with your board vendor as to types and approval ratings. These films are very tough, just ask anyone who has ever tried to scrape through one in order to expose a trace for rework. You will want to make sure that your PCBs are fabricated as SMOBC, or solder mask over bare copper.Tin coatings have a tendency to flow when boards are wave soldered or reflowed, and may weaken the integrity of solder mask. You will also get better performance at high frequencies. As to conformal coatings, there are several issues to consider. The first is cleanliness. No-clean flux leaves a thin film over the PCB surface which will prevent proper adhesion of coatings. Most conformal coatings are intended for protection against moisture and humidity, and voids under the coating won't matter. For arc prevention, the coating must adhere tightly to the board and components. The second issue is how much of the board to coat. Coatings tend to interfere with repairs. Even repairable coatings make the job more difficult, and more importantly, tend to create voids when heated with a soldering iron. If only certain portions of your boards require protection you might consider selectively applying an epoxy potting compound to those areas. I hope that this will be of some help. Scott - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
RE: PCB coating questions
Arjen, Board with only solder mask is considered as non coated. Conformal coating is the type accepted to be allowed to reduce the spacing between trace. However be aware that your safety agency will have to test that coating. The test is described in UL1950 (I do not remember the section and do not have the standard at hand now). Also an audit of your process for applying the coating will be performed periodically. This is in addition to the normal safety audit. Daniel Sicard Compliance Engineer / Ingénieur Certification Transport Systems Business Unit RELTEC Corporation Tel: 514-685-1737 Ext. 4631 Fax: 514-822-4054 Web: http://www.relteccorp.com E-mail: mailto:dsic...@positronfiber.com -Original Message- From: Arjen Dragt [SMTP:adr...@inverpower.com] Sent: Thursday, March 04, 1999 2:59 PM To: EMC-PSTC Listserv Subject: PCB coating questions In looking at meeting CSA and UL spacing requirements for some of our PCB's (in power supplies up to 600 V) some questions concerning the use of conformal coatings (allowing reduction of spacing) have come up. The information that I am seeking is for both CSA and UL; the wording that they use concerning coatings on boards is similar, but not the same. Coatings on a PCB could include both a solder mask, and a strict conformal coating. Does anybody have real-world knowledge as to whether or not a solder mask is accepted by UL/CSA as a coating, and if so, under what conditions? Also, the method by which a coating is applied to a board could have considerable impact on the effectiveness of that coating. For instance, spraying a board will not get at any traces that are buried underneath components, whereas dipping will have a better chance of accessing those hidden areas. The standards that I am looking at say nothing about method of applying a coating (the process). I assume that the decision as to how a coating will be applied is left up to the manufacturer and board supplier. Does anybody out there have best practices that are worth considering when looking at our options for coating methods? Arjen Dragt - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, j...@gwmail.monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
