Sorry I didn't read this one before replying earlier. It's unlikely that the
dielectric constant of the mask changed that much, however the thickness may
have. A cross-section will tell you for sure.

Timothy Reeves
ECD Circuit Board Division
13626 South Freeman Road
Mulino, OR 97042
[log in to unmask]
(503) 829-9108 (800) 228-8198  FAX (503) 829-5482


> ----------
> From:         Tuan Le
> Sent:         Thursday, February 17, 2000 13:16
> Subject:      Re: Soldermask effect on impedance
>
> Thank you for your response, Mike.  However, I guess I wasn't clear on my
> question: I didn't expect the impedance to drop that much after
> soldermask.  Usually I see 2 to 3 ohms the most.
>
> Tuan
>
> -----Original Message-----
> From: Beckman, Michael W [ mailto:[log in to unmask]]
> Sent: Thursday, February 17, 2000 11:54 AM
> To: 'TechNet E-Mail Forum.'; 'Tuan Le'
> Subject: RE: [TN] Soldermask effect on impedance
>
>
> Hi Tuan,
> Just real briefly;  Zo is = to L/C (inductance over capacitance) and
> capacitance is proportional to Er (dielectric constant), so C= Er A/d
> (area)
> over d (distance/separation).
> It is important to understand that solder resist is a dielectric and acts
> as
> insulation to the surface traces, thus reducing the circulating currents.
> I hope this helps.
>
>
>
> Mike Beckman
>
>
> [log in to unmask]
>
> Packaging Engineer
> Assembly Technology Division
> CH5-157                                 Ofc. (602) 554-4232
> 5000 W. Chandler Blvd.            Fax (602) 554-7615
> Chandler, Arizona 85226          Pgr. (602) 340-3983
>
>
>
>
>  -----Original Message-----
> From: Tuan Le [ mailto:[log in to unmask]]
> Sent: Thursday, February 17, 2000 12:13 PM
> To: [log in to unmask]
> Subject: [TN] Soldermask effect on impedance
>
>
>
> Hi everyone,
>
> I have done some tests recently by measuring impedance (on traces from the
>
> coupons) before and after soldermask.  I found that there are quite a
> large
> drop in impedance after soldermask: 4 to 6 ohms for single ended and 8 to
> 10
> ohms for differential impedance.  Has anyone experienced this?  Could
> anyone
> offer me an explanation of what happened?  We use the same Taiyo product
> for
> a long while.
>
> Your help is greatly appreciated.
>
> Tuan Le
> [log in to unmask]
>
>

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