What Sub-Floor material to use for Laminate floor ?

Hello all...
I'm about to install Quick Step laminate floor in our living-dining-kitchen areas. The kitchen and dining areas are vinyl, so I'm going to lay the laminate over that, with the Quick Step Unisound pad directly on top of the vinyl.
The living area is carpet, so once I pull that up, I'll need to build that area up by 1/4" so it's level with the existing vinyl floor, (it's an open concept ranch, so the existing vinyl/carpet interface runs the width of the room.)
My question is, what material and fastening method is best for this purpose? My neighbor works for a flooring contractor, so he can get me 1/4" birch ply at cost. Is it advisable to staple it down, or should I use screws? And how frequently, (what pattern), should the fasteners be placed in.
Thanks for any insight offered, my local flooring retailers are all over the map on this, and Quick Step's web site doesn't offer much info on this topic.
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Use 1/4 inch ply wood. whatever you can find and staples work fine.. no special pattern. I'd put them all over the place so that the floor doesnt pop up or creak in spots. Some plywood has markings on it that tells you where to put nails/staples. every 8 inches I think.

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Definately use screws and ensure the head doesn't stick up above the surface (e.g. countersink or cover with a little floor compound), whatever material you go with. I think backer board is likely the preferred choice for your application. Of course you know what the different floor heights are.

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I was told when laying a subfloor you do not want to screw through and into the joists. I learned this after doing a subfloor in my kitchen. Now when the sun hits it just right you can see the screw marks through the tiles. So try not to hit the joists.

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