X-Authentication-Warning: delorie.com: mail set sender to geda-user-bounces using -f
X-Recipient: geda-user AT delorie DOT com
X-Original-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=20120113;
        h=mime-version:in-reply-to:references:date:message-id:subject:from:to
         :content-type;
        bh=vYgwOz5lEguM2AL9pTHP1mqMAAuqtzceH0OsrUtkE4M=;
        b=kGXCtBFd6lJk30j74HuGB56hfzcq5UKgjSPoLSXAB+9qxbvovLQiFp96vmT6BsfhyD
         gR4LM+RySY5f1D/JCzpLYEo9Su/dxxI+/3pQcpRaTzEKxe/keveoZe2wmKoyZ+OvTdDG
         /GdrzgIEDgQ0NCes5ZLmgWNUJxqU3YapqowZ51vl3X86+yfv/Ae1YjpvSEsXM6b8jiHz
         AEJO0D2/n5QtmCV8O2nUud19evD3nH+E13XbmxKf+Z21+xW4Um1akwjz/D163iK4zW76
         J7nslUgO6PXEHeFjD5XMax4ui/HRZ4Gv5pN766X50OPeDwOZEC4jjVtX5cgXvyHqfaI8
         gL7g==
MIME-Version: 1.0
X-Received: by 10.152.120.164 with SMTP id ld4mr13805373lab.84.1442237322020;
 Mon, 14 Sep 2015 06:28:42 -0700 (PDT)
In-Reply-To: <20150914131629.GB6914@cuci.nl>
References: <20150910201416 DOT GG16766 AT fi DOT muni DOT cz>
	<20150910234211 DOT e718beb2aa1655d22382c8a6 AT gmail DOT com>
	<CAM2RGhSoJTOCovSOfARhH9rWzrPvj2_kP4GVaDG6Zr-910g8mQ AT mail DOT gmail DOT com>
	<201509102207 DOT t8AM7GOh013740 AT envy DOT delorie DOT com>
	<20150914131629 DOT GB6914 AT cuci DOT nl>
Date: Mon, 14 Sep 2015 09:28:41 -0400
Message-ID: <CAM2RGhQrNT-NbXSsuVb_Wjzgd1HWhDR21kLC357wA+yx7bTWKQ@mail.gmail.com>
Subject: Re: [geda-user] 5630 LED footprint
From: "Evan Foss (evanfoss AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
To: geda-user AT delorie DOT com
Content-Type: text/plain; charset=UTF-8
Reply-To: geda-user AT delorie DOT com
Errors-To: nobody AT delorie DOT com
X-Mailing-List: geda-user AT delorie DOT com
X-Unsubscribes-To: listserv AT delorie DOT com
Precedence: bulk

On Mon, Sep 14, 2015 at 9:16 AM, Stephen R. van den Berg (srb AT cuci DOT nl)
[via geda-user AT delorie DOT com] <geda-user AT delorie DOT com> wrote:
> DJ Delorie wrote:
>>> What you want to do is have tons of vias and peel back the mask to
>>> expose more copper to remove the most heat possible.
>
>>It's debatable whether bare (shiny) copper or soldermask can dissipate
>>heat better.  I've heard both ways, although I'm partial to the
>>argument that a matte black mask would be the best emitter.
>
> There are some common misconceptions here (as a physicist, I think
> I can speak with some authority; I don't claim to be infallible though):
>
> The colour of the material, or even the material itself which is
> on the outside (touching the air) does not matter at all with
> regard to heat radiation.
>
> The reason why it's called a black-body radiation is not because
> it radiates better when black.  No, they call it that because a black
> body does not reflect anything *extra* besides the radiation it already
> emanetes.
>
> Does the material matter then at all?  Yes, it does, but only for
> two reasons:
> - If you cover it with soldermask, then the soldermask will carry off
>   a little bit more of the heat to neighboring soldermask.  To maximise
>   this effect it will suffice to simply have no soldermask clearance
>   so that the soldermask touches the sides of the copper.
> - Spots which are not covered with soldermask, which are either
>   tinned or raw copper will not help in radiating more than
>   soldermask covered spots, but they *do* help when receiving
>   incoming radiation.  I.e. they will reflect radiation coming
>   from the outside better than spots covered in soldermask.
>
> So, what is best:
> a. White soldermask.
> b. Soldermask merely touching the sides of the copper (if you
>    want to spread the heat to surrounding soldermask as well).
> c. Leaving as much reflective metallic area uncovered.
> d. Making the metallic area as shiny as possible (tinned is better
>    than raw copper).
>
> But, to summarise, it will only help reflecting incoming radiation,
> it will not matter one iota for primary heat radiation.

Thank you that was a satisfying read.

> --
> Stephen.



-- 
Home
http://evanfoss.googlepages.com/
Work
http://forge.abcd.harvard.edu/gf/project/epl_engineering/wiki/