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SMT electronics assembly manufacturing forum.


DPAK land pattern

#19226

DPAK land pattern | 21 March, 2002

We're having trouble with a TO-252 DPAK from Fairchild (MC7805CDT) and our existing land pattern. The land pattern calculator on the IPC site doesn't have anything available that matches it (there are no TO-252's available on the pull downs), and I've run into a snag creating one.

I have no clue what the field "Z Adj Fact" is asking for, same goes for "Y1 Adj Fact", Y2 Adj Fact", etc. I can only assume it is an adjustment factor (ya think?), but what I'm supposed to be adjusting for, what the unit of measure is (mm, %, etc.) is beyond me.

Anyone with a better understanding of the calculator or a working pattern please give a shout. Thanks.

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#19229

DPAK land pattern | 21 March, 2002

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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#19236

DPAK land pattern | 22 March, 2002

Dave, you are THE master of the search. I made the lame assumption that if they'd had layout specs. for a part, it would be part of the spec. Bad assumption. The layout for the decal from that page you linked to is exactly what I needed.

I looked at the 235A pattern but it wasn't going to fly with this thing. What I created on the calculator was closer, but still no cigar.

Thanks, Dave. Have a beer on me. And make it German, Austrian, or a domestic micro. Doesn't matter to me, as long as you like it.

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Larry Smith

#19330

DPAK land pattern | 29 March, 2002

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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#19332

DPAK land pattern | 29 March, 2002

Thanks, Larry, more good info. I think my designer has that spec. in his library.

What we DID find that while we had the proper pattern called out in our in house spec. sheet for the part, the designers don't look at the spec. sheets. They just grab something that looks right in the existing component library in their cad software, as in "That one looks like it'll work." It saves them 15 minutes, costs us 500 hours over the life of the product. What a deal.

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