Cengiz, theoretically speaking, when you define the thickness of dielectric, = prepreg or core, you ask to your customer for the value after the = pressing phase. So you do not care if the dielectric is core or prepreg, = it is your customer problem how much thick is the initial prepreg to = obtanin the wanted final thickness. Hope this help Carlo -----Messaggio originale----- Da: steve weir [mailto:weirsi@xxxxxxxxxx] Inviato: luned=EC 11 luglio 2005 11.35 A: caydin@xxxxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx Oggetto: [SI-LIST] Re: Impedance deviation due to prepreg shrinking Cengiz, yes the material varies. This is an issue that addresses the = skill=20 and experience of the board fabricator. An experienced shop will be = able=20 to adjust the unpressed stack thickness and copper line width so that = after=20 pressing good impedance control is maintained when the stack-up is=20 reasonable to begin with. Steve. At 12:28 PM 7/11/2005 +0000, caydin@xxxxxxxxxxxxxxxxx wrote: >Dear listl, > >How prepreg layers effect the impedance of >a stripline? To clarify, my stack-up is; > >S1 >-------------- core >-------------- >GND >-------------- prepreg >-------------- >S2 >-------------- core >-------------- >VDD1 >-------------- prepreg >-------------- >S3 >-------------- core >-------------- >GND >-------------- prepreg >-------------- >S4 >-------------- core >-------------- >VDD2 >-------------- prepreg >-------------- >GND >-------------- core >-------------- >S5 > >We assume that pcb cores are hard enough to >achieve the required line impedances. >But, how about the impedances for the striplines >with one core and one prepreg layer as neighbours, >such as GND-S2-VDD1. Is there a rate of deviation after >pcb manufacturing due to prepreg shrinking? Is not it >more problematic if we have multiple core and >prepreg layers? > >Any comments, suggestions? Thank you. > >Cengiz Aydin >Researcher >Bilkent University > >------------------------------------------------------------------ >To unsubscribe from si-list: >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > >or to administer your membership from a web page, go to: >//www.freelists.org/webpage/si-list > >For help: >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > >List FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > >List technical documents are available at: > http://www.si-list.org > >List archives are viewable at: > //www.freelists.org/archives/si-list >or at our remote archives: > http://groups.yahoo.com/group/si-list/messages >Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu