Hello Toby,

I don't believe the thermal relief spokes will cause any EMI problems at all.
The only time I've directly connected to a poured plane like you describe is for quite high current requirements or at very high GHz frequencies.
(the relief structure can form a noticeable LC circuit up there- but 2MHz is a long way below this)
Ask them to calculate the inductance and reactance of those spokes at 2MHz or even 6MHz.

regards, 
Phil.

 
Phil Dutton C.I.D.+
IPC Certified Interconnect Designer

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Toby Carrier
Sent: Wednesday, 14 April 2010 5:07 AM
To: [log in to unmask]
Subject: [DC] SMD Pad Thermal Reliefs

Hi All,

I am reviewing a PCB (after just passing the CID exam Sunday), and have found that there are no thermal reliefs on some surface mount components that are attached to a conductive plane. I have told the designer of the board to add them but they are worried that they will cause EMI problems do to the inductance of the spokes. I do believe this to be an issue since we are talking about a low current low frequency circuit (below 2MHz fundamental and below 1.5A current), but they are still refusing to believe my take on the matter. 

So what does the community think about this problem and have there been any good documents published about thermal reliefs causing EMI problems in low frequency applications?

Thanks,

Toby Carrier
IPC Desingers Council CID

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