Rick,

Let me start off with a disclaimer.  I am not a certified board designer.  My ideas are based on my common sense and years of practical experience.

I have issues with these thermal stress reliefs and the "default" designs.  I would offer that the amount of open space between the pad and the plain be made large enough to effectively separate the pad and the plain.  I've seen cases where the thermal stress relief has been put on a board, but in the interest of the total current capacity needed the open space was all but wiped out by the spokes.  I like the idea of using fewer spokes, that are still up to the current capacity needed for the application, with a large clearance area.  For some large electrolytic capacitors we have used slots for the tabs and might use 6 or 7 spokes for the thermal relief. 

We use both wave and hand soldering for these connections.  For the hand soldering work it is key to size the iron wattage and tip size to the task at hand.  For wave soldering, by using slightly larger open area the thermally relieved pad looks more like a stand alone trace and solders just as well as all the other solder joints.

Just my 0.5 Rubles (2¢)

Phil

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Smith, Richard
Sent: Friday, July 06, 2007 11:54 AM
To: [log in to unmask]
Subject: [TN] Thermal Spokes for Through Hole Pin

Folks,

 

We have a case where the IPC-2222 recommendation for thermal relief
(total .160 cumulative copper web for all layers) is exceeded by the
current carrying requirement of the circuit on a through hole pin. The
IPC specification states that "the total of the thermal relief
cross-sectional area divided by the number of planes connected to the
plated-through hole shall not violate current carrying capacity
requirements for a given hole". Then the spec goes on to state on the
master drawing where this violation occurs in the layout.

 

I was wondering if other folks typically use web sizes greater than the
recommended .160 cumulative. If so, how large? Also, how are these leads
being soldered - hand, wave-flow?

 

Thanks much for your help!

 

Regards,

Rick

 



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