This is a minor update, since there has been some progress done --despite the lack of my spare time.
I am sorry though for the quotes that follow but I have already written the following down in a similar thread:
Ah, do not worry, tinhead! Copy mistakes are in order when reversing even a single-side PCB --not a six-layer one!
For example, I have also spotted a couple of these errors in the Rigol schematics I have posted: The Comparator Hysteresis driver in the "DAC, Demux, Sample & Hold and Buffer" sheet actually is a driver with a 5V0 to 3V3 level-shifter section implemented. By the way, I have de-soldered, cleaned-up and re-balled the Cyclone III FBGA chip, and when I will find some spare time I will draw the digital schematics sleets, too! You see, Rigol has a couple more DAC output signals (a 500.00mHz triangular (not sawtooth) waveform output and a waveform_start(?) signal extra circuitry that do not make any sence to exist in the analog section) that cannot be traced anywhere in the PCB; so, I removed the FPGA to see if these "blind" signals are fed into the Cyclone III.
Though I have not reversed the digital section of the Rigol yet, I think that the Lattice LUT (as well as the CLPD in your device) are RAM address lines generators for the FPGA configuration (which does not seem to have a dedicated address bus for the config. memory, so it probably clocks an external address-bus generator) and the BlackFin that cannot address the 22bit-wide boot-up Spansion FLASH memory alone because it has a 20-bit wide address bus hardware. But I could be wrong; I cannot really tell until I fully reverse the PCB...
What?!? ![Shocked :o](https://www.eevblog.com/forum/Smileys/default/xshocked.gif.pagespeed.ic.CrwtrNUjLO.png)
I am curious to know how do you do that?
With patience! ![Tongue :P](https://www.eevblog.com/forum/Smileys/default/xtongue.gif.pagespeed.ic.J5mTe0A2NA.png)
I think is is time for a
short tutorial on the
BGA and Flat Pachage rework process, using home equipment:
Equipment used: A hot-air rework station, a soldering iron, soldering wick (ERSA 2mm/3mm/4mm wide), flux paste (I prefer the RMA flavor but I've only found a no-clean syringe container at the local stores -that is fine for this job), SMD rework solder-wire (sub-millimeter Alpha-Fry 62/36/2) and flux soldering paste (EDSYN 62/36/2 no-clean).
Remember that the
activated flux (RA/RMA) based products have only a few months self-life, even if stored in the refrigerator.
This is the rework strategy:
1. Preheat the PCB using 130 degrees hot air for 2-3 minutes, to avoid any thermal expansion artifacts,
2. Use conventional (kitchen) aluminium foil to protect the surrounding components, by cutting off a small window to expose ONLY the target chip to the hot air flow,
3. Desolder the BGA using 300..320 degrees hot air, remove the chip and wait for everything to cool down,
4. Clean the old solder, holding the BGA package in a small plastic vice using solder wick and lots of flux; always clean the used flux (I use medical alcohol of 95 degrees or better),
5. Clean the PCB, as above,
6. Reball the BGA with the soldering iron, Ag-containing solder-wire (I use 62/36/2) and lots of fresh flux; always clean the used flux,
7. [Optional step] Reverse the PCB (that takes tiiiiiiime...),
8. Reball the PCB pads as well, as in step (6), since chip re-balling has not provided the pads with enough solder,
9a. Carefully apply flux soldering paste on the PCB pads only and flux at the chip pads, or
9b. Apply flux in lack of flux soldering paste,
10. Carefully place the BGA package on the PCB (in a single move, if possible) and
11. Preheat the whole PCB area around the chip using 130 degrees hot air for 2-3 minutes,
12. Raise the hot air temperature at 280..300 degrees and apply it to the chip in a slow circular motion,
13. Wait for the molten solder
surface tension to move the chip in place when the solder melts,
14. Tap the chip gently towards the PCB, to make sure that all its pads are in contact with the solder underneath,
15. Remove the hot air and wait for everything to cool down naturally (by themselves); always clean the used flux, and
16. Done! Power the device up.
Right now I am at the seventh step...
NOTE: It is not as difficult as it sounds to be; but you need to practice enough before daring to touch your actual device without destroying it!
A second note is about the chip size: As a rule of thumb, use a hot air nozzle of half the diameter of the chip size. For chips smaller than 20mm x 20mm you may skip the PCB preheating step, only if the PCB is very thin. Unfortunately, this is not the case with Rigol's mainboard.
A third and very important note: Always know what you are doing. Always use your common sense! Miracles happen only in fairy tales...
Finally, remember that a good tool is NEVER expensive enough to have it. Just consider the possible extra cost of a damage done by using cheap ("affordable" in the marketing jargon) tools...
-George