Rocky, there are lots of 'it depends', as would say certain can opener. - What kind of product, commercial, MIL, Space, toys etc? These dictate the general requirements - decide low moisture permeability level - decide mobile ions barrier - decide level of repair ability - decide level of encapsulant purity - decide the dielectric constant to match the propagation delay requirements - decide the vulnerability against alfa particles (some semis are) - decide the thermal conductivity - surface tension (vs encapsulant) -decide warpage -others may fill in...lots To use Pertinax or CEM is maybe not an easy task for unexperienced designers, but could be a good idea if you got money and time and lots of go in you. I don't belong to the rigid who say No to every unusual proposal. You have probably seen the 'computers' built on paper and which can be rolled and put in a tube. So, why not make a try. Personally, i know little about paper substrates. So, it's not easy to give a precise advice not knowing the expected final product. I was engaged in COB twenty years ago, very amusing job. There is a lot of litterature about COB, one very good book is this one: Chip On Board edited by John H. Lau ISBN 0-442-014441-4 Van Nostrand Reinhold NY Good Luck Inge On 14 November 2011 14:25, Joyce Koo <[log in to unmask]> wrote: > BT > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Rocky Wang > Sent: Monday, November 14, 2011 3:22 AM > To: [log in to unmask] > Subject: [TN] PCB substrate material choose for COB product > > Hello Technetters; > If there anybody has the knowledge to choose the PCB substrate > material (Paper board, CEM, FR-4) for COB product? For sure FR4 will be > the best. However, why in some case, Paper material work, and in some case, > go to CEM material. If there have some choose guideline, such as from the > die bonding pad size, pad pitch, number of bonding wire, and the size of > the bonding wire or other conditions? > > Best Regards > Rocky > > > ______________________________________________________________________ > This email has been scanned by the MessageLabs Email Security System. > For more information please contact helpdesk at x2960 or [log in to unmask] > ______________________________________________________________________ > > --------------------------------------------------- > Technet Mail List provided as a service by IPC using LISTSERV 16.0 > 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 > For additional information, or contact Keach Sasamori at [log in to unmask] 847-615-7100 > ext.2815 > ----------------------------------------------------- > > --------------------------------------------------------------------- > This transmission (including any attachments) may contain confidential > information, privileged material (including material protected by the > solicitor-client or other applicable privileges), or constitute non-public > information. 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