MOSFET smd - six pins?!

RTQ035N03 in TSMT-6 smd 6-pin package:
<http://www.rohm.com.cn/products/databook/tr/pdf/rtq035n03.pdf
One pin each for source and gate. Four for drain.
Is the number of drain connections simply for convenience of mounting/orientation? One wouldn't need four drains with only one source...
Or am I missing something (which is my default presumption)?
Thanks,
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DaveC
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DaveC wrote:

Thermal dissipation.
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Sue

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Palindrome wrote:

To unpack:
The leads carry heat as well as electricity, and the lead frame is designed to maximize the thermal transfer -- some or all are being made out of copper instead of kovar to maximize heat transfer. To really deal well with the heat you often need to solder the chip down to a copper pour on the board -- the data sheet will tell you how, or will point you to an app note.
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Tim Wescott
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Oh, you mean like this: "Total power dissipation: 1.25w* *Mounted on a ceramic board"
I can find no other references to how to use this chip.
Hmm... how to mount on a ceramic board. Is it difficult to achieve that 1.25w in real-world terms. How many designers use ceramic boards in their designs?
Thanks,
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DaveC
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DaveC wrote:

If you were crazy to $pend the money, then you would be psycho-cramic crack-pot.
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You use ceramic boards in your design when you really need high power densities! For designs where you can run your parts at a lower dissipation per square, you can get away with less exotic substrates like FR4.
Consider the size of a 2-watt through-lead resistor (which is probably what you'd want to use when actually dissipating 1.25 watts), and the space needed to mount it up a bit above the board to allow for adequate air circulation. Consider how warm it's going to get.
Now, consider all of that heat coming out of a little SMD package, with no free-air under-chip circulation, being carried away mostly by radiation and by conduction into the PC board traces. That chip's going to get hot!
I've seen some of the less-expensive PC-board material be singed pretty badly from the heat of a TO-220 7805 linear regulator which was screwed down (with its heatsink) directly to the board. Even with a couple of square inches of heatsink sticking up into the air, its several watts of heat dissipation burned the board. The heat-per-square density of a 1.25-watt SMD is likely to be even higher, and thus mandates the use of a high-temperature-tolerant board substrate.
As I understand it, it's not necessarily any harder to use a ceramic board than a glass/epoxy board. You just tell your fab house which substrate to use, and use a somewhat larger wheelbarrow to ship them the money :-)
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Dave Platt < snipped-for-privacy@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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snipped-for-privacy@radagast.org (Dave Platt) wrote in

Off topic to FET's but how much, roughly, for small quantities of maybe 2" x 3", single sided? And can thickness be had at 1/8"? This could be a cost- effective method for mounting electronics and optics on a single board for laser designs where it is critical that thermal stability is high, and expansion is low. I've seen it used in the Coherent C315M laser, and it looks like a good way to do it. It seems to allow high quality for making small numbers of devices by hand, and an easy way to set and reset alignments at will, so even if it costs a bit, it might save far more than it costs.
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Dave Platt wrote:

I find that Megtron 6 holds up rather well at high temperatures and it is a heck of a lot less expensive than ceramic and certainly not brittle!
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To, not, clarify. Most of the power dissipated in your mosfet is dissipated in the drain.
The chip is put into the package with the drain bonded to the main leadframe and the main leadframe has most of the leads connected to it so you can get the heat out.
How they think you do that is up to them and the marketing department, who will win.
How you do it is up to you.
I've got problems with spelling dissapated dissipated but, fortunately, that's not your problem. It's rather similar to your subsequent question(s)......
DNA
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gui.ntli.net:

Good, cos 'dissipated' is the way to go... Can we enjoy enough dissipation? I think not. Cut me some SLACK. >:)
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I haven't seen this thing, so I don't know if my suggestion has any merit, but just possibly... TEC. The small ones often found in modest quantites on eBay. Small high pump density devices metallised both sides are often custom made, so surplus turns up at times. If you could remove the tinning, and somehow protect the body of the device in peelable rubber, you could etch tracks and such onto the top side for mounting stuff. That gets you a cheap ceramic heatsink AND a pump. :) And an easy way to mount the parts, if you have a temp-controlled iron.
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