DPAK land pattern

In the beginning, there was TO-5. And it was good. Flushed with success, they created TO-220. It too was good. Then came SMT. It was better than some things, but then again ...

In these early days, there was a haze on the horizon that blocked the sun and there was much strife. So, rather than create new packages, they bent the leads of established devices in bizarre new fashions and called them strange and wonderous names.

So it came to pass, the bent-leaded TO-220 became a TO-252. And this, some anointed 'Deca-watt PAcKage' (Hitachi transistor) or 'DPAK'. Although, some [others] might take umbridge this last poyl of wisdom. Not whether it is a �pearl of wisdom�, but that the attribution is true. There seems to legions vying for the right to claim the birthright of 'DPAK'. Anywho, that�s my story and I�m sticking to it, as Oil used to say.

Following Dave�s hierarchy for developing SMT pad designs, buried someplace in the fine SMTnet Archives [search on � rlp]: * First choice: go to http://www.fairchildsemi.com/ds/MC/MC7805.pdf that describes your component. Then somehow go to http://www.fairchildsemi.com/products/discrete/pdf/dpak_1dim.pdf that further details the packaging, including the pad design. * Second choice: Use SM-782 [or go to IPC land calculator and use a standard package, like TO-252 / TO-262]. It�s the second to the last one, just after 'Tanalum Capacitor' and before 'TSOP'. [Hint: The RLP for a TO-252 is 235] �Existing JEDEC (Joint Electronic Device Engineering Council) package types can be accessed on-line via JEDEC Publication 95 "Registered and Standard Outlines for Solid State and Related Products" at http://www.jedec.org .� * Third choice: Use the IPC Calculator to make your own design, as you're attemping to do. It�s possible that "Z Adj Fact" "Y1 Adj Fact", "Y2 Adj Fact", etc are fudge factors that you supply to adjust the amount of solder the ends-up in the solder connection you design [like how high the solder rises up the heel], but I don�t have clue. �For technical assistance contact John Perry, at 847-790-5318 or email: perrjo@ipc.org

NOTE: Brian and Neil have never allowed us to link to email from the SMTnet Forum. So, you'll have to cut / paste John Perry's address into your other emailer. Sigh.

One final point. Fairchild [Intersil] is redesigning these packages, as we speak. Though I can't fathom what they're talking about in their description of what they plan to do, I'd be surprised if they are messing with the pads, rather playing with the lead to plastic interface or the plastic or something else. Forewarned is something or other.

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The IPC-EM-782 reads as follows: the adjustment factor is usually intended to increase the Z dimension slightly, but brings the Z maximum up to an even equivalent. Example if Zmax is 2.100mm then you would enter an adjustment factor of .100mm. The adjustment factor is added to the Zmax dimension and you will end up with 2.200mm. The same thing goes for the G and X adjustment factors. If you need more info on the calculator you can order IPC-EM-782. This is the manual for the land pattern calculator.

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