Joe,
I'm not sure if it matters whether you use pad or lead area. How much difference do you expect to see between the two areas? I don't think it will be enough to overcome the approximations that are inherent in this simple ratio.
If you really want to get a good prediction, you'll want to look at the geometry of the solder joint and the amount of solder joint surface area (surface tension is stronger than cohesive forces within the bulk solder - so a BGA would be better off than something with fewer, larger leads totaling the same area). And you may also want to consider the impact that flux residues may have if you don't clean the assembly between reflows.
So if you think a component is near the limit, it may be easier to just run the assembly through the oven and see what falls off.
Ben
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Friday, June 06, 2008 10:04 AM
To: TechNet E-Mail Forum; Gumpert, Ben
Subject: RE: [TN] Double side reflow query
Good morning All,
Is "P" really equal to the total "pad" area or total component "lead" surface area for leaded parts which would in my opinion include the foot, heel and sides of leaded parts? I can see P = to pad area for BGAs but not for leaded components unless you just want to keep it simple and use the pad area. Comment?
Best Regards,
-joe
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gumpert, Ben
Sent: Friday, June 06, 2008 5:29 AM
To: [log in to unmask]
Subject: Re: [TN] Double side reflow query
Prashant,
TechNet strips attachments.
A rule of thumb is that to keep parts from falling off:
R = C/P (g/in) must be 30
Where
C = Component weight in grams
P = total pad area in square inches
Ben
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of prashant chopra
Sent: Friday, June 06, 2008 7:52 AM
To: [log in to unmask]
Subject: [TN] Double side reflow query
Hi,
We are having a PWB wherein, we have a potentiometer and 3 PLCC package on the bottom side of the PWB.
I need help to know if there would be issue of these components falling off during the second reflow process (when top side is being reflowed)?
We not have options to move these on the top side as there are already other PLCC and BGA packages eating up the PWB land area.
Let me know your comments and also on how can we prevent these from falling off during the second reflow process?
I am attaching the data sheet for both these parts above.
Thanks, in advance to all of you for your help and precious time.
Rgds
Prashant
Bollywood, fun, friendship, sports and more. You name it, we have it on http://in.promos.yahoo.com/groups/bestofyahoo/
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