I worked at a company that produced several products per month, all of which needed to pass FCC A and B,
and this might have happened to us if we ever went back to the lab once we initially had the boards pass
test, but since we only took are boards to have them tested until they passed it wasn't a problem.  I do
however know for a fact that because manufactures process, materials etc vary so much it is possible that
your layer structure from vendor "A" used a combination of materials, and spacing that resulted in an
impedance controlled board, and vendor "B" was different.  Also turn around time should be taken into
consideration.  If you set up your board design layer stack-up for impedance control also include in your
fabrication requirements a way of verifying it. A cross-section / micro-section works really well for doing
this.

Paul Brionez wrote:

> ? Has anyone had the pleasure of  a design that was tested and passed FCC
> Class A & B ,miserably fail when we order a small prototype run of these
> same multilayer PCBs for a quick turn from a different vendor. "We do not
> specify our layer dielectric thicknesses by default."  Please share with me
> you experinces and solutions I would appreciate any feedback that I can get.
>
> Thanks
>
> Paul Brionez
> Sr. PCB Designer
> Cherry Electrical Products
> 11200 88th Ave
> P.O. Box 581913
> Pleasant Prairie, WI 53158-0913
> PH 414-942-6659
> Fax 414-942-6334
> Pager 414-318-9964
> [log in to unmask]
>
> ################################################################
> DesignerCouncil E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
> ################################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
> To subscribe:   SUBSCRIBE DesignerCouncil <your full name>
> To unsubscribe:   SIGNOFF DesignerCouncil
> ################################################################
> Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
> For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
> ################################################################

################################################################
DesignerCouncil E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE DesignerCouncil <your full name>
To unsubscribe:   SIGNOFF DesignerCouncil 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################