Joe



Phil Zarro [[log in to unmask]] and Bob Willis [www.bobwillis.co.uk] are two of
the people that has have written articles on the topic.  Check their sites.



Dave Fish



----- Original Message -----
From: "Macko, Joe @ IEC" <[log in to unmask]>
To: "'TechNet E-Mail Forum.'" <[log in to unmask]>; "'David Fish'"
<[log in to unmask]>
Sent: Monday, June 30, 2003 5:57 PM
Subject: RE: [TN] Double-sided reflow with Altera RQFP...


> Dave,
>
> Interesting calculation.  I have never seen the numbers worked out.  Is
this
> calculation and your ratio documented in a reference book or something?
> Does the formula also apply to BGAs?
>
> Some of our new designs have BGAs on both sides which I am evaluating.
>
> Look forward to your reply.  thanks
>
> joe
>
> -----Original Message-----
> From: David Fish [mailto:[log in to unmask]]
> Sent: Monday, June 30, 2003 1:38 PM
> To: [log in to unmask]
> Subject: Re: [TN] Double-sided reflow with Altera RQFP...
>
>
>
> Hi Steve
>
>
> We don't double reflow this part. We wouldn't consider it without a
fixture
> or some other support.
>
>
> You know that sound, the almost involuntary sound that patrons in a
> restaurant make when a waiter drops a glass or a tray? It's kind of an
> "oooooo" sound. Well if you run these parts, the sound that the troops at
> your plant will make will be so loud as those pups start Peter Panning to
> the floor that the people in the front will stop playing games on the
> computer and walk out back to find-out what's going on.
>
>
> Do the numbers:
> * Part weight: 15.1 gm
> * Lead toe to heel: 0.46/0.66 mm
> * Lead width: 0.17/0.27 mm
>
>
> Lead wetting area = 240* [0.46*0.17] mm^2 = 18.7 mm^2 [0.03inch^2]
> Weight of component to total pad mating area ratio: 15.1 gm / 18.7 mm^2 =
> 804.6 mgm per mm^2 [519.1 gm per inch^2]
>
>
> A commonly acceptable ratio is: 50 mgm per mm^2 [30 gm per inch^2]
> Pushing the boundary ratio is: 44 gm per inch^2
>
> Dave Fish
>
> ----- Original Message -----
> From: Steve Gregory <mailto:[log in to unmask]>
> To: [log in to unmask] <mailto:[log in to unmask]>
> Sent: Monday, June 30, 2003 8:42 AM
> Subject: [TN] Double-sided reflow with Altera RQFP...
>
> Mornin' All!
>
> Just a quick question, has anybody ever done a double-sided reflow with a
> 240-pin Altera RQFP on the bottom that has a metal heatsink in the top?
>
> Thanks!
>
> -Steve Gregory- ---------------------------------------------------
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