As noted last month, virtually all the semiconductor devices in the PIC/AVR Programming Adaptor are surface-mount, apart from the diodes and LEDs. This approach has been taken otherwise the PCB would have been impractically large.
Even so, the double-sided PCB is fairly densely populated on the top-side and has quite a few SMDs underneath as well. However, we have specified SMDs with a “reasonable” pin spacing so they should not be too challenging to solder.
The double-sided PCB measures 116 x 127mm and has plated-through holes and vias. The PCB is available from the SILICON CHIP Partshop and is coded 24105121. It isn’t practical to make the board yourself, given the number of vias, especially as some of them are located under components. The boards we provide not only have plated through-holes but also a solder mask and a silk-screened overlay on both sides to make construction as easy as possible.
Figs.4(a) & 4(b) show the component overlays for both sides of the PCB. Install the surface-mount parts on the top first. You can refer to the panel later in this article for a step-by-step procedure on hand-soldering SMDs.
Note that most of the SMD components are static-sensitive and so you should ideally build it on an anti-static mat or using some other method to prevent damage to the Mosfets and ICs.
Fig.4: the overlay diagrams for both sides of the PCB. Install the parts as shown here, paying close attention to the orientation of the ICs, Mosfets and electrolytic capacitors. Pin 1 is shown with a dot in one corner of the IC but in some cases there may be no dot and instead, a bevelled edge on the IC package indicates the side with pin 1.
Start with the three small dual diodes (D6-D8) and then fit the four 2N7002P Mosfets. These diodes and Mosfets look virtually identical so be careful not to get them mixed up.
Follow with the 13 FDS6912A dual Mosfets that go on the top of the board. They are in 8-pin SOIC packages and are not all orientated in the same manner so check carefully that each one is the right way around before soldering it in place. These Mosfets usually have both a bevelled edge on one side of the package and a dimple to indicate pin 1 – the position of both is shown on the overlay diagram.
There are also 13 ICs (including REG4) on the top of the PCB and they go in next. Again, their orientations vary so you should check each one carefully. Some of the ICs may have a dot or dimple indicating pin 1 but some will only have a bevelled edge so that is the most reliable way to tell which way they go in. Many of the ICs are in identical packages so take care that each type goes in its designated location.
Regulators REG2 and REG3 can now be fitted. Solder the three pins and then the tab. Don’t get the two mixed up. Then you can fit the passive SMD components, which consist of eight 100nF ceramic “chip” capacitors, two 220nF ceramic capacitors, three 10µF ceramic capacitors and one 0.1Ω SMD resistor/shunt.
It’s now time to fit components to the other side so fit the four tapped spacers at each corner on the top side of the board, using M3 x 6mm screws. That done, flip it over and it will rest flat and level on the spacers rather than the components you have just finished soldering.
Refer now to Fig.4(b). There are a further 12 FDS6912A dual Mosfets so fit them now. Again, be careful with orientation as it varies. Follow with the five remaining ICs and then the three passive SMD components: one 10µF and two 100nF ceramic capacitors. You can then remove the tapped spacers and refit them on the other side of the board, in preparation for the next step.