Doesn't anyone supply prepreg with 104 glass? Should start at 2 each ply and reduce some at pressing. Fills the traces because the resin content is very high. Chuck Brummer Charles W. Brummer | 3M Manufacturing Engineer 3M Electronic Solutions Division 3M Canoga Park, 8357 Canoga Ave. | Canoga Park, CA 91304 Office: 818 734 4930 [log in to unmask] | www.3M.com This message (including any attachments) may contain material, non-public information or proprietary information and is for the intended recipients only. If you are not the intended recipient, you should notify the sender and delete this message. Any disclosure, copying, or use of this information is strictly prohibited and may subject you to legal liability. From: Tan Geok Ang <[log in to unmask]> To: <[log in to unmask]> Date: 08/03/2011 08:28 PM Subject: Re: [TN] PCB dielectric - 2 layers prepreg Sent by: TechNet <[log in to unmask]> Agreed but maybe I should rephrase my question. To meet a thickness of 3.5mils, what I know is that the fabrication process will need at least 2 prepreg to meet this requirement. Believed not under the following prepreg material 106, 1080, 2113, 2116, 7628. -----Original Message----- From: Frank Kimmey [mailto:[log in to unmask]] Sent: Monday, 1 August 2011 10:11 PM To: 'TechNet E-Mail Forum'; Tan Geok Ang Subject: RE: PCB dielectric - 2 layers prepreg I think mostly for fill. As an example, 1080 prepreg starts at about 3.5 mils and after pressing is about 2.5 mils. This means there is about 0.5 mils per side to fill in etched areas on adjacent layers. That is less than 1/2 oz copper (currently IPC considers 1.2 mil thickness per oz). Poor fill will aid in delamination and poor reliability. Use of 2 sheets will allow more resin to flow towards needed fill areas giving better bonding. Also resin content on thinner prepregs is usually higher allowing more resin flow to use for fill A Designers understanding of why Frank N Kimmey CID+ Manager - PCB Design Powerwave Technologies Inc Mobile - 916-670-0645 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Tan Geok Ang Sent: Sunday, July 31, 2011 6:50 PM To: [log in to unmask] Subject: [TN] PCB dielectric - 2 layers prepreg Hi All, In one of the Class 3/A Exception Requirements, it indicates that for "Dielectric Thickness of 0.089 mm [0.0035 in] minimum with 2 layers prepreg if not specified on drawing.", what is the reason to use 2 layers prepreg, what is the advantage over a single layer? Thanks. Regards GA Tan ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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