I upped my pledge, when filling in the survey after the Tsunami was funded, to include the 10-bit (edit: 12-bit) DAC (because why not, and it gives me the option to install it or not). However, I am wondering about the practicalities of installing it.
Is this going to need a hot air rework station (to remove the old DAC)? Does the new one go on with paste, or can you use cored solder and a soldering iron? What other components are nearby which might be dislodged or damaged by hot air soldering?
Basically a small amount of "it will be fine, it's easy" handholding/reassurance would be welcome. Or alternatively, some "unless you have experience of SMD rework, leave this well alone or get someone else to do it" would be fine, too.
Suspect I am not the only one wondering about this.
Desoldering the DAC will require hot air or chipquik. It's possible to dislodge other parts when using hot air, but if you're careful it's not an issue - and if you do, it's easy enough to put them back into place.
Soldering the replacement part won't require paste - you can use the 'flood and wick' method. It's a bit fiddly, but not outrageously so.
Given the enormous popularity of the DAC upgrade, I'm considering offering it as a preinstalled option - but I'm still working out how to price it, and if it could be something that's stocked on an ongoing basis.
Note that the description for the BackerKit DAC item is for the 12 bit DAC not the 10 bit.
Another possibility for removing the original DAC, if you don't mind destroying it, is to cut all the pins and then individually desolder the part of each pin left on the board. I've been successful with many different packages, cutting each pin, one at a time, with a sharp utility knife.
Thanks for the responses! Yes, destroying an 8-bit DAC is not going to trouble my conscience. Although I should probably get a hot air station at some point. And yes it was indeed the MCP4922 12-bit version. I have usd those in DIP. The INL is a bit odd, its ok for the 10bit, very good for the 8 bit and not great (2LSB typ, +/-12LSB max) for the 12bit version.
Preinstalled could be an interesting option, depending as you say on pricing (and the impact of stocking multiple versions).
I'd recommend getting yourself some ChipQuik - it is actually much easier for beginners than hot air, and I find it amazingly good for removing devices with large themal mass without affecting nearby parts.
Similarly, I'd also recommend against the use of a utility knife to destructively remove the old device - it is far too easy to damage nearby PCB tracks. Using side cutters for detructive removal is quite safe, but doesn't work well on SMD parts.
Have you actually tried this method and ended up damaging PCB tracks? The copper on PCBs is surprisingly robust, and it doesn't take much force to cut the thin pins of a TSSOP package, slowly and carefully, one at a time.
If you cut on the vertical part of the leg, towards the body of the chip itself, then the blade doesn't even move towards the PCB. If you're forced to cut downwards, due to space limitations, most of the time there's the large pad, that the pin is soldered to, underneath. The size, and the fact that the pad is usually coated with solder, makes it difficult to cut through it.
If the part only has two rows of pins (as in this case), sometimes you can use the blade on one side and then bend the chip up and cut the other side with side cutters, or vertically with the blade.
Since we have the schematics and board layouts for this device, it's easy to do visual examinations and continuity tests on all the pins and surrounding traces before soldering the new part. In the unlikely event that a trace has been cut, the blade is so thin that the resulting cut could easily be repaired with a solder bridge.
That said, I'd be using hot air, since I already have the tool and can save the original part.
I hadn't heard of this before, but a spot of googling shows a company called Chip Quick who have a variety of products, including Solder / Desolder Complete Kit (lead-free) at €120.00. Is that what you were suggesting?
Basic hot air stations seem to go for about €70.00 or so.
Yes, and I've seen others do it and damage the board. The damage can be almost invisible, and can be to a track that is continues underneath the chip, and thus may be difficult to find and repair after replacing the chip. The solder and pad for most SMD parts doesn't extend under the legs very much, so it wont provide a cushion to the blade when travelling straight down.
Using the blade to cut upwards or sideways can avoid problems, but as you say space limitations can make that impractical. It also isn't an obvious thing to do for a beginner.
So while it is quite a good technique if done with care and knowledge of what can go wrong, I don't think it is for beginners. For larger pins, side cutters work well, but most side cutters wont be able to get in between TSSOP pins.
No, not that expensive kit. That is for pro's wanting a complete setup.
One of these ones: http://www.chipquik.com/store/index.php?cPath=200 (SMD1 or SMD1NL)
Available from DigiKey, Mouser, etc, so you can possibly combine with your next parts order.
e.g. DK lead free: http://www.digikey.com/product-detail/en/SMD1NL/SMD1NL-ND/1164266
Sparkfun used to sell it, but they retired it. Still some useful info, video, & comments on the retired product page.
But, as I said, we'll have schematics and the board layout, so it's a trivial matter to do a continuity check before replacing the chip. If you can see well enough to solder in a TSSOP package, then you should be able to also visually inspect the 7 traces under the chip for physical damage, with a loupe, microscope, or other magnifier.
However, before attempting this method for real the first time, I'd recommend practising with a similar package on a damaged or otherwise to be discarded electronic item (obsolete PC motherboard or peripheral, VCR, etc.) to determine if you are comfortable with doing it.
Cutting the pins is certainly a cheaper method than Chip Quik®, or hot air if you don't expect to use it enough for a good return on investment.