I don't believe there is any IPC standard regarding minimum pieces of prepreg to form a dielectric. It is a legacy requirement by some customers in believing that single prepreg between two copper layers is less reliable. It may be true but difficult to enforce nowadays because 1) with increasing # of layer, you don't always have the space to put two or more prepreg. 2) in the low cost region, the manufacturers always choose single prepreg if possible to save cost. Customers have every right to specify minimum of two prepreg. But if they did not give you such requirements before you made the boards, I don't think the products are rejectable at this point. Best regards, Jason Zhao VP of North America Operations Sunshine Global PCB Group US Cell 510-468-4412, China Cell 131-62722392 www.sunshinepcbgroup.com -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Francesco Di Maio Sent: Sunday, October 19, 2014 5:00 PM To: [log in to unmask] Subject: [TN] Number of prepreg foils between copper layers Hello Technet, I am looking to understand if there is an IPC standard where is specified the minimum number of prepreg foils that should be put between two PCB layers. I know that IPC 6012C (par. 3.6.2.15) specify that the minimum dielectric spacing is 90um and that the supplier choice the number of prepreg layers, but I was wondering if there are other standards that may specify this statement. I have a case where a Customer is expecting that a minumum of two prepreg foils should be put between copper layers. Does anyone know in which IPC standard I can find criteria where is stated that a minimum of two prepreg foils should be used and why ? Which benefits ? Thanks in advance for your help. Best Regards Francesco Francesco Di Maio GEST labs - Via Kennedy Ingresso 2, 20871 Vimercate (MB) - Italy E-Mail:[log in to unmask] ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________