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]



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