Electronic – Covering PCB Pads

It is a pretty low parts count design, but it is by no means simple. It helps to understand how the chip works inside to see what pins are more sensitive to stray EMI than others before doing a layout. Then you can determine where coupling to ground is useful and when it can interfere. ( This is just learning curve info not specific to your layout) Although many students use the physical layout approach, it defies logic and when you want to understand how it works, you need to use logic in your schematics not just physical layout. This is most useful when it doesn't work.

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When you discover the load regulation is poor due to the layout of the external transformer in relation to RFB feedback, which schematic will you follow and how will you discover why it fails in your layout. Unfortunately what schematics do not show is the equivalent circuit of a ground plane and its coupling. This is why a more "Logical" schematic is important and rules for small inductive loops is important and coupling to ground planes. Although I concur with your aadvice given, this design will be very noisy and suffer in regulation becuase of how the boundary mode processing works inside the chip. A more reliable design will use large voltage feedback thru a tertiary winding (which they use in msome aqpplications)

It may work, but how well is the question.

EMI radiation, Load regulation, Step response and ripple are important measures of performance which are affected by this clever chip's internal processing of the current waveform using the MOSFET resistance. When it fails you can try to understand how it works. With your schematic, all you can do is see that the parts are connected to the right pin.

These basics although may seem tedius to you, they are critical to getting the perfromance offered by the chip. Layout is critical in this design because of the simplified external feedback of transient switching. I would use a small planar SMD torroidal transformer such as the one used by Linear Technology and follow their layout guidelines.

A stainless steel stencil will help, probably a good deal, with the printing of fine pitch parts. The ones with the bends on the sides (like the ones you pointed to) tend to be stiffer than the ones without the bends (like the ones that pcb-pool include for free with board orders. The latter can bow in the center and cause some problems with printing. I don't think it will help as much with production time as you want it to, unless you count wiping off the bad prints and redoing it with the plastic stencils.

Depending on your level of production, you might consider a real manual stencil printer for use with framed stencils, like

These, of course, use framed stencils, so you'll have a $500 one time cost for the printer, and about $300 NRE for the framed stencil. Storage of the framed stencils may eventually become an issue.

There are also steps you can take in board design that can help. Make sure there's room for solder mask in between pins on fine pitch parts, if you can, and your process will be a bit more forgiving. Also, adjust the apertures in the cream layer to be a bit smaller if you're hand printing with less than great stencils. This can be a pain to do, especially if you want to do it only for SOME parts using some PCB packages. In eagle, for example, for fine pitch parts I set SMD pads as NOCREAM, and I add the cream aperture manually for each pad (I generate a macro to do this in octave, and run the macro in eagle).