Retro CPC Dongle – Part 7

In my last post, I reviewed the board that came back from OSH Park. Within a week I’d also received my stencil from OSH Stencils. Seriously impressive guys! Last time I ordered it took a month to arrive in Australia, this was a week and a half. Not only that, I opted for both the plastic and the stainless steel stencil to compare the fine detail on each. The plastic stencils are fine for larger print, but on my last project, I struggled to get the solder paste to print through the fine 0.4mm holes for the BGA. I may be able to apply more pressure to the steel stencil to get the paste through. Here’s the nice little package from OSH Stencils.

Note the nice little touch with the solder paste spreader and the OSH Stencils sticker for your laptop/bike/pencil case.

The plastic stencil shows some issues with the fine detail on the HDMI connector (top right), while the steel stencil resolves this detail nicely. Have a look at a close-up.

Click for more

The holes for the FPGA are in focus for this macro view, and you can see they resolve very nicely. Unlike the plastic stencil, the steel stencil should be good for a few prints if I decide to make a number of these boards.

The solder paste I ordered from RS Components is good for features down to 0.5mm or below (according to the information sheet), so I’m hoping this will print the small features on the SDRAM, which uses 0.8mm spacing and 0.4mm pads (bottom center right of image).

The other features are over 0.5mm so I don’t expect there will be a problem. I can always use by ‘blob and streak‘ method of spreading the paste.

I have also now placed my order with Mouser for the components. I realised that Mouser give you the option to save and share your order, so if anyone is interested in building this board, I may be able to share the same order form in the same way that OSH Park allows sharing of designs.

The only gripe I have is that Mouser stopped selling the ADV7513 video chip that is key to this project. Why, Mouser, why? RS Components has plenty of stock and it was available at a reduced price too, so I ordered three and will keep two in my spares stock.

Once the components arrive, I’ll do a test layout placement on the board to make sure the footprints are correct, then I’ll apply the solder paste and replace the components then bake in the IR oven. The test layout is needed because if I have any footprints wrong, I’ll need to clean the solder paste off every component and store away until I can get new boards made with the correct footprint.

The next couple of weeks are pretty exciting, so stay tuned! I’ll try to post regularly and will include a record of the construction process, with some images.

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