A couple of months ago, I bought some ADF4351 synthesizer boards at a very attractive price from a Chinese supplier. Sadly, the supplied boards turned out to have fake, or out of spec, 4351 chips which actually behaved like 4350s, with no /32 or /64 divisor. As a result, it was impossible to use them below about 130MHz. Several UK microwavers including RadCom columnist Andy Talbot G4JNT were also supplied with these fakes
Following up Andy’s suggestion in his Design Notes column in the Nov 2016 RadCom , I decided to swap one of the fake devices for a new ADF4351BCPZ bought from RS (stock no 796-8710, £9) and can confirm that the board now behaves correctly at /32 and /64. It just needed a bit of concentration, a fine soldering iron, lots of flux and a stereo microscope, then a 100W iron to flow the solder into the heat transfer pad from the underside.
I removed the fake chip by applying the 100W iron to the underside of the board beneath the chip, then used a hot-air blower to melt the solder on the top side of the board, lifting the chip away with tweezers. Next, I applied a good dose of liquid flux, then cleaned off the pads with desolder wick. I applied a bit of solder to one of the pads, then more flux, positioned the new chip, melted the solder to attach the device with the chip firmly held down, then did the same at the opposite side, but followed the technique recommended by Andy and others, using a flood of flux and a fair excess of solder.
I ran the iron across all of the pins and pads on each edge of the chip, then removed the excess using desolder wick, ensuring I cleared all bridges. Surface tension did the hard work, although I did have to reflow two of the pins after close examination under the microscope.
The repaired board is in the picture. The chip is 5mm square.