10 Oct
2015
10 Oct
'15
11:10 a.m.
Wow. A pretty board indeed. Thanks for showing it off. This is also
interesting to me since a friend and I have been talking about building
something rather similar (and entirely different at the same time, we're
just focusing on the mass storage function and using an FPGA). I'm
curious about some things though, if you'd be willing.
Bus drivers (along with voltage level conversion) have been a problem.
You seem to be using 74LVC parts. Are they close enough? Though I also
see a bunch of FETs down there.
I've used OSHPark in the past for small boards but for 45 sq.in. boards
they'd seem to be awfully expensive, even if using their medium run
pricing. The fingers look gold plated. It could be just the ENIG
finish but I also see little tails running off the bottom as if you're
setup for hard gold plating. Does OSHPark have that capability?
I gotta say that I'm impressed with your soldering skill as well as
stamina. I was going to ask if it was machine assembled but I see in a
later message that it wasn't. 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.
I'm curious why you didn't use resistor networks instead of discrete
components.
I also love that your design tool put omegas on the silk screen for the
resistor values.
-Dave
10 Oct
10 Oct
5:50 p.m.
On 2015-10-10 2:10 PM, David Bridgham wrote:
Wow. A pretty board indeed. Thanks for showing it
off. This is also
interesting to me since a friend and I have been talking about building
something rather similar (and entirely different at the same time, we're
just focusing on the mass storage function and using an FPGA). I'm
^^ A popular idea. I've been kicking around the same idea with friends
for 10 years now. :(
Need to find time...
--Toby
curious about some things though, if you'd be
willing.
Bus drivers (along with voltage level conversion) have been a problem.
You seem to be using 74LVC parts. Are they close enough? Though I also
see a bunch of FETs down there.
I've used OSHPark in the past for small boards but for 45 sq.in. boards
they'd seem to be awfully expensive, even if using their medium run
pricing. The fingers look gold plated. It could be just the ENIG
finish but I also see little tails running off the bottom as if you're
setup for hard gold plating. Does OSHPark have that capability?
I gotta say that I'm impressed with your soldering skill as well as
stamina. I was going to ask if it was machine assembled but I see in a
later message that it wasn't. 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.
I'm curious why you didn't use resistor networks instead of discrete
components.
I also love that your design tool put omegas on the silk screen for the
resistor values.
-Dave
9:53 p.m.
On Sat, Oct 10, 2015 at 11:38:45AM -0400, Paul Koning wrote:
Did you check the PHY latency for GigE? I know
it's insanely large for
10G-BaseT, but I don't remember if GigE is still reasonable.
I was worried about that, since other PHY data sheets list high-ish numbers
(hundreds of nsec) as if that's good news. But I can't find any mention
of latency at all on the Micrel data sheet. (I chose this part just for
coming in a TQFP package that I can solder.) So I guess I'll just try it.
Hopefully if the thing works at all, at least it'll support programmed I/O
and interrupts. DMA would be nice but it'll have to have very fast
turnaround, which will probably need hardware help on the PC end (and
anything for PCIe is a much fancier project -- PEX 8311 or a big FPGA).
On Sat, Oct 10, 2015 at 02:10:25PM -0400, David Bridgham wrote:
Bus drivers (along with voltage level conversion) have
been a problem.
You seem to be using 74LVC parts. Are they close enough? Though I also
see a bunch of FETs down there.
I'm hoping the 74LVC244s will work for receiving (I've used them for
TTL levels before), even if technically they don't follow the bus specs.
I have a lifetime stock of DS3862Ns (which do) but I'd rather go RoHS.
Yes the drivers are FETs, with gate resistors to slow down the rise/fall
times a bit.
I've used OSHPark in the past for small boards but
for 45 sq.in. boards
they'd seem to be awfully expensive, even if using their medium run
pricing.
Yeah it was $218.75 for three of these. Which is a lot, but then again no
it isn't, given the size. And they do such beautiful work... Also I feel
bad about all the puny adapter boards they've done for me, where they
probably lost money.
The fingers look gold plated. It could be just the
ENIG finish but I also
see little tails running off the bottom as if you're setup for hard gold
plating. Does OSHPark have that capability?
Not that I know of. This is just ENIG and won't last long. What look like
tracks leading off to a plating bar are just me trying to be cute by
imitating DEC's finger shapes.
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'm curious why you didn't use resistor
networks instead of discrete
components.
In this case I wanted to have FETs to disconnect both legs of each
terminator for when the board is being a peripheral (so a bussed R-network
wouldn't work), and anyway discrete resistors are cheaper and easier to
find in any value and wattage. More sqinches but it's going to be a
dual-height whether it's full of parts or not so that's no problem.
Has anyone tried active termination on DEC busses? I'm not sure how
to make the terminator power supply "weigh" enough to quickly resist
pulls in either direction, especially if it's a switcher.
I also love that your design tool put omegas on the
silk screen for the
resistor values.
It didn't want to! Each one of those is two superimposed strings, one with
spaces where the omega goes, and one in the "Symbols" font with the omega
(or mu). OCD is its own reward. Well I really do like being able to stuff
a board this size w/o looking at the schematic or parts list even once.
John Wilson
D Bit
12 Oct
12 Oct
8:30 a.m.
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 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.
paul
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? 
8:57 a.m.
On 10/12/2015 10:30 AM, Paul Koning wrote:
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.
Jon
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 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 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?
9:12 a.m.
On Mon, Oct 12, 2015 at 11:30:39AM -0400, Paul Koning wrote:
Sure, but I've been using the new solder (and paste) for years now, and I'm
resigned to it. I'd sell any of my doodads if someone wanted to buy them,
so I want them to be legal, even though I've never understood who was being
poisoned by the lead in solder. I absolutely hated it at first (and I
still hate paying for it -- my last 1 lb roll of Kester RoHS solder with
water-soluble flux was over $100) but I've gotten used to it and really,
it's fine. Nice shiny strong joints, if I run the iron a little hotter.
And the SMT stuff is all reflow so it's automatic.
... 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 would think a pick & place robot would be a
fairly straightforward
derivative of a 3d printer.
I was thinking the same thing. A vacu-sucker head and some way of feeding
(and unwrapping) the tape with the components, and possibly a camera, are
all it needs ... not that that's trivial, but it's nothing compared to the
X/Y/Z mechanics. Also, 500 gallons of new firmware, but, whatever!
But is that really needed? Placing the parts isn't
all that terrible.
I wholeheartedly disagree! It took me over four hours to position the
parts on this board and my back was killing me by the end. (I can't
*believe* I made it four hours w/o knocking the board off the table or
putting my elbow on it or something idiotic like that.) I wouldn't even
mind a very sloppy robot that doesn't have machine vision and isn't precise
about orienting parts. I always go over with a microscope and square them
up anyway, and that part doesn't take long (and gives a nice OCD buzz).
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.
It works *fantastically*. That's what I do, using an Arduino and a homemade
shield with a MAX6675 on it (um ... hand-soldered, but SOICs are easy so
there's no chicken/egg problem), and a couple of buttons and a socket for
an eBay LCD module. The only thing is, the (bare) tip of the thermocouple
has to be touching one of the boards (if it's just measuring the air temp,
you scorch the PCBs), and no matter how I think I've bent it, it has a mind
of its own and tends to sweep components away when I put it in place and
let go.
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.
Those are huge time-savers. I've had great luck with both ohararp.com
(charged by the sheet) and oshstencils.com (by the sqinch) for Kapton
(low-volume), and bayareacircuits.com (by the design) for stainless steel
(super nice but more expensive). A small Corian cutting board makes a
great backboard for taping up the jig to do some pasting.
For one-offs, using a syringe by eye is fine. It doesn't have to be very
precise. The flux melts at a much lower temp than the solder pellets, so
the beautiful square blocks from the stencil turn into a pool anyway, but
then the solder mask does its job and the pool separates out onto the pads
(except for TQFPs -- gotta use solder-wick afterwards on them) once the
tin melts too. So for SOICs/TQFPs you might as well just lay a bead down
across a whole row of pads. It works just as well as a tiny dab on each.
John Wilson
D Bit
3359
days inactive
3361
days old
5 comments
5 participants
participants (5)
-
dab＠froghouse.org -
elson＠pico-systems.com -
paulkoning＠comcast.net -
toby＠telegraphics.com.au -
wilson＠dbit.com