George and Rich, I have a memo from UL that they accept UL Recognized multilayer boards in lieu of the tests in 2.9.7. Basically they state that the bond strength tests in UL796 (standard for PWBs) are not equivalent to the bond strength tests in Clause 2.9.7 of UL1950, but that the multilayer board is accepted as a Recognized Component meeting US component standard. However, for supplementary or double/reinforced insulation reuirements you must ensure compliance with the minimum 0.4 mm distance through insulation requirements.
Best Regards, > > > Hi George: > > > > Along this line, I was asked, if placing power and ground traces on > > separate (PCB) layers would be an acceptable way of reducing clearance > > requirements between (gnd&pwr) traces. Is there anyway to anticipate > > clearance between PCB layers of a multi layered board? Is there a need to > > as far as 950 is concerned? I haven't been able to find anything that > > mentions this. > > Supposedly, the insulation between traces on separate PCB layers > should constitute solid insulation (not clearance). Therefore, > the requirements of Sub-clause 2.9.4.1 should apply. Depending > on the insulation, the 0.4 mm requirement for reinforced solid > insulation may apply. (There is no dimensional requirement for > solid basic insulation.) > > This is a three-dimensional problem. The 0.4 mm applies in all > three dimensions with respect to plated-through holes. Also, at > the edges of the board, the construction must meet the applicable > creepage distance if the inner layer conductors extend to the edge > of the board. > > The issue is complicated by certification houses who require > proof that the insulation bonds within the board comply with > Sub-clause 2.9.7, "spacings filled by insulating compound." > This sub-clause requires proof that no voids or cracks are > likely in the solid insulation provided by the prepreg layers. > Such PCB multilayer construction may be difficult to prove. > > You should take up this question with your certifier, as the > applicability of the requirements to multi-layer PCBs may vary > with the certifier. > > (UL 1950 Second Edition "Application Guidelines," number 2.9.4-001 > implies acceptance of multi-layer glass fiber PCBs as supplementary > or reinforced insulation between layers. However, this same > guideline does not appear in the current "Guidelines.") > > I'm surprised the PCB design would require power and ground on > separate layers. Most primary power circuits can be adequately > insulated from ground without using multi-layer technology. In > my experience, the only use of ground in power supply circuits is > for the return of the Y capacitors, which need not have 25-amp > capability. But, if the power circuit is a secondary power circuit, > then such construction may effectively use multi-layer technology. > > > > Best regards, > Rich > > > > ------------------------------------------------------------- > Richard Nute Product Safety Engineer > Hewlett-Packard Company Product Regulations Group > AiO Division Tel : +1 619 655 3329 > Effective 6/12/99: +1 858 655 3329 > 16399 West Bernardo Drive FAX : +1 619 655 4979 > Effective 6/12/99: +1 858 655 4979 > San Diego, California 92127 e-mail: ri...@sdd.hp.com > ------------------------------------------------------------- > > > > > > --------- > 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). > 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).
