Overall thickness of the board is a A-list criterion (needs to be met, before you can dig deeper into meeting circuit performance issues). This is "macro" criteria, which also includes no delam, dryness, etc. Otherwise you just throw the panel away, preferably as soon as possible before sinking more cost into it. These primary concerns are effects of prepreg performance and prepreg selection. He probably had "issues" in the past, and either he or his supplier blamed it on proper build-up. Jim Paulus at Itron: 507-837-4326 at office: 608-787-0817 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Brooks,Bill Sent: Tuesday, July 13, 2004 1:31 PM To: [log in to unmask] Subject: Re: [TN] 7628 prepreg? Thanks Paulus, I typically do not specify which resin system or particular prepreg to use unless there is a specific need. Typical FR4 construction meets the needs of almost 99% of the boards here. This particular 4 layer design is working in the 150 Mhz range, so I can't see it being particularly sensitive to impedance matching, the wave length is approximately 2 meters (6.5 feet) a quarter wavelength would then be about 1.625 ft. or almost 20 inches. So I find it unlikely that this 50 mil trace that the designer used would act anything like the intended 50 ohms impedance in the circuit. It probably closer to 80 ohms but it's so short that the change in impedance would still be very negligible to the circuit. The trace is about 2 inches long. I'm left scratching my head trying to figure out why he/she decided to call out the prepreg layers in the stackup by part number unless the only thing they wanted to do was control the distance from the outer top layer to the inner ground plane just beneath it... But it could be they were working on false assumptions... and may have had little or no effect on the electrical performance of the board at all. I would like to see a good presentation on board stack up and its affects on designs. If anyone knows of one in our area in Southern California, please let me know. We could use some better guidelines to help in the formation of the notes controlling stackup parameters on our boards and fabrication drawings. Maybe we could avoid having future 'head scratching' sessions here... Best regards, Bill Brooks PCB Design Engineer , C.I.D., C.I.I. Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 http://pcbwizards.com -----Original Message----- From: Paulus, Jim [mailto:[log in to unmask]] Sent: Tuesday, July 13, 2004 10:40 AM To: [log in to unmask] Subject: Re: [TN] 7628 prepreg? To add to J Bush's comments: FR4 resin Dk is 3.5 and E-glass is 6.5 (approx), with the mixture being in the 4.2 (60+% resin) to 5.3 (35% resin) range. Your 031" laminate (assume core is actually 028") is 38-40% resin on 4-7628. But the 7628 prepreg is 45-48%, so there's some difference to be accounted for (although Bush is correct in that the impedance is not hughly affected.) Prepreg dielectrics will be different thicknesses depending on the conductor layer(s) facing them. 2 plies of typical 7628 pp against near-solid ground plane on one side and copper foil on the other will press out at 7.5+ mils/ply. Another variable is lamination -- 170 psi in a vac press may not squeeze out much resin, leaving a thicker and flatter dielectric. Copper foil thickness is another. Most laminators have dielectric calculators to figure out predicted thicknesses based on factors such as conductor thickness, signal vs grd, etc. Repeating a basic tenet, laminators do not use the same prepreg in their laminates that they sell for bond plies. Resin content and flow properties are adjusted to fill and bond layer details -- 3-D space w/holes, canyons, etc. Laminate plies are low RC and low flow, because they're only building a flat 2-D structure. So you can't assume the same values for mechanical and electrical properties for dielectrics made with core lamiante vs prepreg. Jim Paulus at Itron: 507-837-4326 at office: 608-787-0817 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Jeffrey Bush Sent: Tuesday, July 13, 2004 12:18 PM To: [log in to unmask] Subject: Re: [TN] 7628 prepreg? I see a .014 spacing (yield is actually ~.013" since resin is used to fill some of the plane geometry) with a microstrip line thickness of .0012" (0.5 oz + plate) will yield ~ a 50 OHM value with a .022" line. 7628 is glass rich and has a slightly higher Dk, but in a build like this the Dk variation only effect the impedance by a few %. Using 7328 is preferred in this build since the predicted yield is stable verses using multiple plies of a resin rich build that produces a much higher standard deviation in thickness. Designs requiring higher frequencies with smaller lines - example in this case a .005" dielectric with a .007" line yields the same impedance value, but will tend to have a higher variation then the first build, although the resulting characteristic impedance is more stable at higher frequencies due to the resin content of the dielectric. Jeffrey Bush Director, Quality Assurance and Technical Support 76 Technology Drive - POB 1890 Brattleboro, Vermont 05302-1890 Tel. 802.257.4571.21 Fax. 802.257.0011 [log in to unmask] http://www.vtcircuits.com -----Original Message----- From: Brooks,Bill [mailto:[log in to unmask]] Sent: Tuesday, July 13, 2004 12:46 PM To: [log in to unmask] Subject: Re: [TN] 7628 prepreg? So in a stackup that requires a .031 core with 2 oz. Cu both sides and a symmetrical build up of 2 layers of 7628 on both sides (4 total) and then 1.5 oz Cu finished outside... Would the objective then be to control the spacing from the outer conductors to the inner ground plane at .014 in.? Is the DK of 7628 different than other glass epoxy materials? I would like to calculate the impedance of the traces on this board. Is there a materials sheet available on-line that describes the electrical and physical characteristics of the prepreg material? And does it change when laminated? This is an older board and I'm just trying to decipher the designer's intent. Thanks in advance... Bill Brooks PCB Design Engineer , C.I.D., C.I.I. Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 http://pcbwizards.com -----Original Message----- From: Jeffrey Bush [mailto:[log in to unmask]] Sent: Tuesday, July 13, 2004 4:10 AM To: [log in to unmask] Subject: Re: [TN] 7628 prepreg? 7628 glass has different yield thickness based on resin content and the rheology. You can purchase 7628 in epoxy from a yield per ply thickness of .0065" to where you are with yours. 7629 glass can give you up to .009" in yield as this is some what heavier glass. I think the standard has been a .007" per ply yield - this is fairly standard from laminate suppliers. Jeffrey Bush Director, Quality Assurance and Technical Support 76 Technology Drive - POB 1890 Brattleboro, Vermont 05302-1890 Tel. 802.257.4571.21 Fax. 802.257.0011 [log in to unmask] http://www.vtcircuits.com --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- This message was scanned for viruses!! --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- This message was scanned for viruses!! --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------