Q-bus I/O project
elson at pico-systems.com
Mon Oct 12 10:57:57 CDT 2015
On 10/12/2015 10:30 AM, Paul Koning wrote:
>> On Oct 11, 2015, at 12:53 AM, John Wilson <wilson at dbit.com> wrote:
>> ... but I'd rather go RoHS.
> I would recommend against that. Not unless you are trying to create a commercial product where you *must* be RoHS to conform to the requirements of the bureaucrats. Use real solder -- the job will be much easier and the result more reliable. Real solder is still available, including solder paste.
> I asked one of the technicians at work about this stuff a while ago -- they know all about this question since they have to use RoHS when doing rework on modern designs. And what I just said is what they told me (i.e., don't, unless you are forced to). They also told me that real solder works just fine on lead-free parts. I tried that and can confirm this is correct.
>>> I was hoping for the Pick 'n' Paste machine to come along and save me from
>>> having to do all that by hand but that project seems to have faded away.
>> Oh seriously! I've been hoping one of the homebrew SMT assembly robot
>> projects would "take" too, at a reasonable cost. Making prototypes is
>> bad enough ... but what if I get it working and then I'd want to make
>> dozens of these things, at 4+ hours each?
> I would think a pick & place robot would be a fairly straightforward derivative of a 3d printer. But is that really needed? Placing the parts isn't all that terrible. The trouble is the soldering. I have read (and posted here in the past) a nice article (in German) on the use of a toaster oven with some clever temperature control as an IR reflow soldering machine. I haven't tried this yet, but it sounds like a good scheme, and would allow the use of BGA parts at least in moderate sizes.
> At least one of the moderate cost small volume PCB fab shops will deliver solder paste screens along with the finished boards if you ask for it.
I have moved over almost entirely to lead-free. Yes, there
is more hassle, but I ship boards all over the world, so I
do have to be compliant. At first, I had HUGE problems, but
it got better with more experience, and as the makers of
solder got it all figured out. I use SAC305 solder, which
wets better and has a shinier finish than pure tin solders.
I have a 1600 Lb. Philips CSM84 pick and place in my
basement. I can do one-offs by hand, as long as the parts
aren't too small, but for more than a couple boards, I
really DO want the P&P machine. But, it is not just a 3D
printer. it has 3 heads with different nozzle sizes for
different parts, two of them have centering jaws that center
the part on the nozzle after it is picked up. it also has a
sort-of camera to pick up fiducial marks on the board for
alignment, and a centering station that centers large parts
like FPGA chips. The big difference is that it has a huge
amount of recovery software to detect mis-picks (by vacuum
level) and try to readjust the part by cycling the jaws, if
that doesn't work it dumps the part and tries another one.
The toaster oven reflow soldering is amazing. I use a ramp
and soak controller with a thermocouple poked into a through
hole in the PC board for temperature reference.
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