Message

Hi Alexis,

 

EMI control is very dependant on many interactions between circuit features, shielding, return paths, low inductance grounding, etc... and there are conducted and emitted types of electromagnetic interference. Changing trace widths might compromise the spacing to ground or an adjacent trace. I know when I was at REMEC, I worked in the C-band (2 GHz to 6 GHz) range and a 5% change in trace geometries could significantly alter the performance of an edge coupled filter or RF mixer or combiner, or coupler in the circuit.  Unless I knew the science that went into the design, I wouldn't 'fix it' if it's not broken.  However, if the cost impact savings is substantial, I would go to the CCB and propose the alternate solution as a cost reduction enhancement, after careful review by the EE's and RF Engineers.

 I know that really doesn't answer your question in general, except to say 'it depends'...  but it would take serious analysis of the board design to know how to address this particular question. I must assume you are working with cell phone technology in the hand held market or the cell switching relay site market. I'm not sure what frequencies that encompasses. I should but it has been a while since I worked in those frequencies at PCSI. But as frequency increases, the sensitivity to circuit geometries increases as well. So the caution still stands.

 

It may be, and I am speculating, that the core and layering is not as sensitive to these minor changes proposed, but I would not take it on the advice of the board shop, without careful review and circuit analysis in the responsible RF engineer's hands. He/she has the ability to review the proposed changes and look at the impact to the design. One way to approach this would be to have the board shop do a prototype run with different colored solder mask, RED for example,  to prevent them from getting into the production units, and do some serious testing of them. Maybe someone else has a different viewpoint... but I would not give the board shop 'cart blanc'.

 

Best regards,

 

Bill Brooks
PCB Design Engineer , C.I.D., C.I.I.
TITAN CORPORATION
DATRON WORLD COMMUNICATIONS DIVISION
3030 Enterprise Court, Vista, CA 92083
Email: [log in to unmask]
Website: http://www.dtwc.com/
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
_______________________________________


Member of the San Diego Chapter of the IPC Designers Council
Communications Officer, Web Manager
http://dcchapters.ipc.org/SanDiego/
http://home.fda.net/bbrooks/pca/pca.htm

 

-----Original Message-----
From: Alexis Meehan [mailto:[log in to unmask]]
Sent: Thursday, June 05, 2003 2:41 PM
To: [log in to unmask]
Subject: Re: [DC] Core thickness/emissions

 

            Thanks for the input. Yes, these layers have impedence control, and yes, the fab house also requested

            changing trace widths in order to meet the impedence requirements. In this case, do you still think the

            emissions would change? I'm curious, because other engineers at previous companies have OK'd this

            type of request with no disastrous results (that I KNOW of!).

            Thank you for your feedback.

-----Original Message-----
From: ext Brooks,Bill [mailto:[log in to unmask]]
Sent: 05 June, 2003 02:21 PM
To: [log in to unmask]
Subject: Re: [DC] Core thickness/emissions

Alexis,

 

The impedance value is set by the relationship of the signal trace width and its distance through the specific dielectric with its inherent characteristics to the return path of that signal, (i.e. ground plane, etc.). If you change the core thickness of the board, you must also verify that the relationships of the signal to return path have not varied, otherwise you will get unexpected electrical performance results from the board. If the fabrication drawing specifies the cores and layering structure, I would not deviate from that without an ECO. The comments about test are very valid, you may be unwittingly requiring your engineering test department have to re-do a complete DVT (Design Verification Test) all over again and loose what ever money the board vendor wished to try to save you on this particular run of boards.

 

I would not give the PCB board shop the authorization to deviate. Find another vendor or get this one to sign up to the fabrication drawing requirements.

 

Best regards,

Bill Brooks

-----Original Message-----
From: Alexis Meehan [mailto:[log in to unmask]]
Sent: Thursday, June 05, 2003 1:50 PM
To: [log in to unmask]
Subject: [DC] Core thickness/emissions

 

Recently a board shop asked to use a different thickness of core material than what

we called out on one of our boards (they wanted .009 instead of .006, and .006 instead

of .008). Our engineer was reluctant to agree because EMI testing had already been

done on the prototype and had passed with the cores we called out. Does core thickness

have a noticeable effect on emissions? I haven't seen this as a problem before. Any

feedback would be appreciated. Thanks.

 

~~~~~~~~~~~~~~~~~~~~~~
Alexis Meehan                     
PCB Design Manager 
NOKIA                
Nokia Internet Communications 
Desk Phone 650.625.2124        
Cell Phone 650.892.2572          
~~~~~~~~~~~~~~~~~~~~~~

 

 

 

--------------------------------------------------------------------------------- DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil. To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 --------------------------------------------------------------------------------------------------------------------------------------------------------- DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil. To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 --------------------------------------------------------------------------------- ---------

--------------------------------------------------------------------------------- DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil. To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 --------------------------------------------------------------------------------- DesignerCouncil Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF DesignerCouncil. To set a vacation stop for delivery of DesignerCouncil send: SET DesignerCouncil NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 --------------------------------------------------------------------------------- ---------------------------------------------------------------------------------