Homebrew PCBs

I've always just had someone else make/assemble a surface mount board
whenever I needed it for work (being a theorist means you don't do
that much real work) but I'm interested in building my own now.

I read the following articles:

http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=59
http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=58

and want to try the skillet method.

The paste stenciling seems geared toward faster production.  Is it
possible to just get a syringe and dab a small amount of solder paste
to each pad without getting a stencil / squeegee for experiments/1 off
boards or do you need a stencil to reflow?

I've always just used through hole components whenever prototying my
own boards and hand soldered the smt.  This led to a few things:
1) I spend way too much time minimizing discrete resistors/caps
because I hate soldering them
2) I hate hand soldering smt even more so I minimize their use

Hopefully if I get the smt to work it seems it's much easier to use
lots of smt discrete components as you just lay them on top and it
solders itself.

Any tips would be appreciated.  Thanks!

Henry Liu <henryjliu@...> writes:
> The paste stenciling seems geared toward faster production.  Is it
> possible to just get a syringe and dab a small amount of solder paste
> to each pad without getting a stencil / squeegee for experiments/1 off
> boards or do you need a stencil to reflow?

Yes, you can use a syringe.  I've done that plenty of times.  Not as
predictable as a stencil, but it certainly does work.

If you have a photo-UV home-etch setup, you can make stencils with
aluminum foil pretty easily.

IMHO you want an aluminum hot plate if you can.  I got a cast iron
one, and the heat pattern was very uneven.  I eventually got an
aluminum plate to put over it, and although it now takes longer to
reflow, the results are much more consistent.

> 2) I hate hand soldering smt even more so I minimize their use

SMT is easier than PTH because you don't have to keep flipping the
board over.  You just need to find a method that works for you.

For discretes, the "best" hand-solder way is to pre-solder one pad for
each part, then use one hand for the iron and the other for tweezers.
Place each part and reheat the solder to attach them to the board.
Then go back and solder the second pad on each part.

> Hopefully if I get the smt to work it seems it's much easier to use
> lots of smt discrete components as you just lay them on top and it
> solders itself.

Yeah, that's the way :-)

>
> Yes, you can use a syringe. I've done that plenty of times. Not as
> predictable as a stencil, but it certainly does work.

Does the drop size matter?
Does it need to flat?

>
> If you have a photo-UV home-etch setup, you can make stencils with
> aluminum foil pretty easily.
>

Any links to the aluminum foil method?

I saw http://www.pololu.com/ will print mylar pretty cheap.

Some people seem to use a cricut machine
http://www.instructables.com/id/Create_Solder_Paste_Stencils_with_Cricut/

Finally, you can buy a laser cutter on ebay for about $1000-$1500 if
you're doing this often.

Henry Liu <henryjliu@...> writes:
> Does the drop size matter?

A little, but as long as they're consistent you'll be OK.  It's when
you have one big one and one little one that you risk tombstoning.
Look for a diameter about half the size of the pad.  For TQFP or TSOP
parts, just run a bead along the pads and clean it up later with flux
and solder wick.

> Does it need to flat?

No.  You'll squish it down with the part anyway.

> Any links to the aluminum foil method?

Laminate UV film on both sides, expose, develop, etch (takes a few
seconds).  DO NOT STRIP.  The thickness of two films plus the foil is
just right for stencils and strong enough for a few boards.

> I saw http://www.pololu.com/ will print mylar pretty cheap.

I just used this service with good results, with 0.5mm pitch TQFPs:
http://www.ohararp.com/Stencils.html

He uses kapton instead of mylar, because the laser won't warp it.

Instead of a skillet I bought a cheap electric cooking plate and put
an aluminium plate on top. The temperature is controlled with an
industrial controller (thermocouple sensing on the aluminium plate). I
put the boards on only after the plate has reached stable temperature.

I tried a stencil when the board house offered it free with the PCB,
one board turned out quite good but for the second the stencil didn't
lie flat and it was a mess. I'll stick to the syringe in the pneumatic
dispenser for now. If you do more than ones and twos the stencil
probably pays off.

ST

On Fri, Jul 24, 2009 at 9:26 PM, DJ Delorie<dj@...> wrote:
>
> Henry Liu <henryjliu@gmail.com> writes:
>> Does the drop size matter?
>
> A little, but as long as they're consistent you'll be OK.  It's when
> you have one big one and one little one that you risk tombstoning.
> Look for a diameter about half the size of the pad.  For TQFP or TSOP
> parts, just run a bead along the pads and clean it up later with flux
> and solder wick.
>
>> Does it need to flat?
>
> No.  You'll squish it down with the part anyway.
>
>> Any links to the aluminum foil method?
>
> Laminate UV film on both sides, expose, develop, etch (takes a few
> seconds).  DO NOT STRIP.  The thickness of two films plus the foil is
> just right for stencils and strong enough for a few boards.
>
>> I saw http://www.pololu.com/ will print mylar pretty cheap.
>
> I just used this service with good results, with 0.5mm pitch TQFPs:
> http://www.ohararp.com/Stencils.html
>
> He uses kapton instead of mylar, because the laser won't warp it.
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>
>

What's a good pneumatic dispenser?  If it has an electronic on/off
switch, I hook it up to my cnc with a relay +  M code switch.

I think if I do it a lot then I'll just program my cnc machine to do
it like this guy: http://www.youtube.com/watch?v=HdqVt0jCBHk

I think it's pretty easy, just move X,Y,Z down activate dispenser,
move up Z and move to next XY in a loop.

If I can source a good vacuum pump lift I can place the part too.  I'm thinking:

Pick and place machine
1) put components randomly on flat white background on top of rotary
table (http://www.sherline.com/8700inst.htm)
2) mount camera on CNC spindle
3) segment image
4) detect lines using hough transform
5) rotate plate using rotary table to align lines either 90 degrees or 0
6) resegment image to find centroids of objects
7) move spindle over and pick it up with vacuum chuck
5) drop it on centroid of pcb

I write image recognition software all day long at work so the
software is no problem but not so sure about the lift/drop.

I think I'm getting ahead of myself though as I probably will only
make a few boards a year lol.

Too many projects, too little time...

Cheers,
Henry

> I tried a stencil when the board house offered it free with the PCB,
> one board turned out quite good but for the second the stencil didn't
> lie flat and it was a mess. I'll stick to the syringe in the pneumatic
> dispenser for now. If you do more than ones and twos the stencil
> probably pays off.
>
> ST

Stefan Trethan <stefan_trethan@...> writes:
> Instead of a skillet I bought a cheap electric cooking plate and put
> an aluminium plate on top.

That's what I've got too.  No temperature control, though - the
warm-up curve is good enough for me as-is.  I *do* have to let it cool
down between boards, though.  I put the board on it when it's cold,
turn it on, and six minutes later everything reflows and I slide the
board off.

I've found hand syringe dispensing to be pretty forgiving. Sometimes I even connect both pads of an 0805 with the paste on accident (momentary loss of dexterity). So far it has always reflow process has always sucked the paste back onto the pad and has never left me with a short.

Also I have been using Cash Olsen's technique (site now defunct) where you only heat the skillet up to 100 or so degC and then pop each component with a heat gun for a few seconds. The down force of the air will mitigate tombstones, but there is there is the danger of blowing the component off the board completely if you get the gun too close.

Good luck!
Royce

--- In Homebrew_PCBs@yahoogroups.com, Henry Liu <henryjliu@...> wrote:

>
> >
> > Yes, you can use a syringe. I've done that plenty of times. Not as
> > predictable as a stencil, but it certainly does work.
> 
> Does the drop size matter?
> Does it need to flat?
> 
> >
> > If you have a photo-UV home-etch setup, you can make stencils with
> > aluminum foil pretty easily.
> >
> 
> Any links to the aluminum foil method?
> 
> I saw http://www.pololu.com/ will print mylar pretty cheap.
> 
> Some people seem to use a cricut machine
> http://www.instructables.com/id/Create_Solder_Paste_Stencils_with_Cricut/
> 
> Finally, you can buy a laser cutter on ebay for about $1000-$1500 if
> you're doing this often.
>

On Fri, 2009-07-24 at 14:21 -0400, DJ Delorie wrote:
> 
> Yes, you can use a syringe. I've done that plenty of times. Not as
> predictable as a stencil, but it certainly does work.
> 
> If you have a photo-UV home-etch setup, you can make stencils with
> aluminum foil pretty easily.
> 

Was posted here before an url by a member with his impressive photos of
solder stencils made just drilling holes on a metal sheet in the center
of each pad. Unfortunately didn't saved the url to find it now. 

Seems a very simple way off doing it. And the method seems to be quite
capable of controlling solder amount. The needed software maybe very
known but don't look so difficult to archive too.

Now i found it anyway searching for stencil in the list messages.
http://www.pbase.com/eldata/stencils

Henry Liu wrote:
> What's a good pneumatic dispenser?  If it has an electronic on/off
> switch, I hook it up to my cnc with a relay +  M code switch.
>   
Positive displacement pumps are the most accurate, time/pressure would 
probably be good enough.  Epoxy is often dispensed with a stamp, that 
might work for you.
> I think if I do it a lot then I'll just program my cnc machine to do
> it like this guy: http://www.youtube.com/watch?v=HdqVt0jCBHk
>
> I think it's pretty easy, just move X,Y,Z down activate dispenser,
> move up Z and move to next XY in a loop.
>   
That's how I drill my boards.  I use a commercial XY table, and a home 
built Z stage with a Dremel attached.  A PIC receives NC drill data from 
a laptop and drives steppers with Allegro A3955 chips.  After it mills 
out the board, I transfer toner and etch.
> If I can source a good vacuum pump lift I can place the part too.  I'm thinking:
>   
The Laurier machines I worked on (HA225, HA250, DS3000) used a venturi 
when house vacuum wasn't available.
> Pick and place machine
> 1) put components randomly on flat white background on top of rotary
> table (http://www.sherline.com/8700inst.htm)
> 2) mount camera on CNC spindle
> 3) segment image
> 4) detect lines using hough transform
> 5) rotate plate using rotary table to align lines either 90 degrees or 0
> 6) resegment image to find centroids of objects
> 7) move spindle over and pick it up with vacuum chuck
> 5) drop it on centroid of pcb
>
> I write image recognition software all day long at work so the
> software is no problem but not so sure about the lift/drop.
>   
The lift and drop are easy, but unless vision software has made amazing 
strides in the last 10 years, you need parts to be at least close to 
correctly oriented.  With the Acumen system we used, +/-15\ufffd was about 
all you could expect.  And watch out for vibration.  Parts can slide 
while the rotary table moves if they aren't in a Gel-pack.
On the HA225, we offered a manual procedure.  A Lazy Susan centered 
under the camera with a pedestal with parts on it sitting on that.  Find 
the part, rotate, step on footswitch.  Worked great.

Kerry

> I think I'm getting ahead of myself though as I probably will only
> make a few boards a year lol.
>
> Too many projects, too little time...
>
> Cheers,
> Henry
>
>   
>> I tried a stencil when the board house offered it free with the PCB,
>> one board turned out quite good but for the second the stencil didn't
>> lie flat and it was a mess. I'll stick to the syringe in the pneumatic
>> dispenser for now. If you do more than ones and twos the stencil
>> probably pays off.
>>
>> ST
>>

"roycepipkins" <royce.pipkins@...> writes:
> So far it has always reflow process has always sucked the paste back
> onto the pad and has never left me with a short.

I had a friend over doing his first place-n-reflow (it was going to be
his board, after all) and I answered many of his concerns with "relax,
it will magically fix itself during reflow."  Of course, it did :-)

Flux and surface tension is a winning combination!

Simao Cardoso <simaocardoso@...> writes:
> Was posted here before an url by a member with his impressive photos
> of solder stencils made just drilling holes on a metal sheet in the
> center of each pad. Unfortunately didn't saved the url to find it
> now.

I did that for one board I made, it worked fine.  But it doesn't work
for me with 0.5mm pitch TQFPs because my drills aren't small enough.
And it's faster to do it with etch if there are a lot of holes to
drill.

DJ Delorie wrote:

> I did that for one board I made, it worked fine. But it doesn't work
> for me with 0.5mm pitch TQFPs because my drills aren't small enough.
> And it's faster to do it with etch if there are a lot of holes to
> drill.

Ok it's easier for who own a cnc router. There is also some spray or so
of peelable silicone soldermask for making this, need to be exposed and
developed. 

Stupid thought: Using dry film? Tin don't like NaOH, and melting the
solder will harder the dry film...

What are the cheapest sockets for BGAs ?
     ( ball grid arrays )

Might one be able to adapt a socket from a socket 775 CPU ?

Best

Gus S. Calabrese
Denver , CO

The six minutes warmup time is what frightens me off, I know it is
only at peak temperature for a much shorter period but still....

Now, how to go about doublesided SMD soldering on a hotplate? Would it
work to prop the board up by the corners with spacers and just let the
heat rise into it? I've seen commercial hotplates that have kind of a
lid to trap heat like in a small oven.

ST

On Fri, Jul 24, 2009 at 11:15 PM, DJ Delorie<dj@...> wrote:

> That's what I've got too.  No temperature control, though - the
> warm-up curve is good enough for me as-is.  I *do* have to let it cool
> down between boards, though.  I put the board on it when it's cold,
> turn it on, and six minutes later everything reflows and I slide the
> board off.
>

----- Original Message ----- 

From: "AGSCalabrese" <agscal@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Saturday, July 25, 2009 12:23 AM
Subject: [Homebrew_PCBs] Cheapest sockets for BGAs


> What are the cheapest sockets for BGAs ?
>     ( ball grid arrays )
> 
> Might one be able to adapt a socket from a socket 775 CPU ?

None of them are cheap!

Leon

AGSCalabrese wrote:
>  
> 
> What are the cheapest sockets for BGAs ?
> ( ball grid arrays )
> 
> Might one be able to adapt a socket from a socket 775 CPU ?
> 

I take my hat off to anyone using a high pin count BGA on their home 
brew PCB. 0.5mm pitch quad flat no leads (QFN) is furthest I've dared to go.

Adam

Stefan Trethan <stefan_trethan@...> writes:

> The six minutes warmup time is what frightens me off, I know it is
> only at peak temperature for a much shorter period but still....

Seems to work OK for me.  Given it starts at room temp, not all of the
six minutes is "hot".

> Now, how to go about doublesided SMD soldering on a hotplate? Would it
> work to prop the board up by the corners with spacers and just let the
> heat rise into it? I've seen commercial hotplates that have kind of a
> lid to trap heat like in a small oven.

You can do double sided in an oven, but for hotplate, I just manually
solder the few back-side parts.

I've done 0.5mm CSP (5 pins) but I'd rather not do even those.

> For discretes, the "best" hand-solder way is to pre-solder one pad for
> each part, then use one hand for the iron and the other for tweezers.
> Place each part and reheat the solder to attach them to the board.
> Then go back and solder the second pad on each part.

I was thinking about this and can't I just pre solder all the SMT tabs
then apply flux and the part on it then bake it or use a skillet?

My main problem with hand soldering is that I leave the chip on top
long and over heat it or I can't get all the pads at once and it
bulges up.

For this reason they make SMD solder paste - flux mixed with powdered solder.

ST

On Sun, Jul 26, 2009 at 10:46 AM, Henry Liu<henryjliu@...> wrote:

> I was thinking about this and can't I just pre solder all the SMT tabs
> then apply flux and the part on it then bake it or use a skillet?
>
> My main problem with hand soldering is that I leave the chip on top
> long and over heat it or I can't get all the pads at once and it
> bulges up.
>

Henry Liu <henryjliu@...> writes:
> I was thinking about this and can't I just pre solder all the SMT tabs
> then apply flux and the part on it then bake it or use a skillet?

I don't think it will be sticky enough to hold all the parts in place
as you move the board around.  Once you've soldered the pads, you have
a hard bump that wants to move the part *away* from alignment, whereas
solder paste can be flattened and is sticky to hold the parts in
place.

I routinely do qfn and 0603 parts using homemade stencils and a toaster oven that has been converted to a reflow oven. I make the stencils by drilling holes in thin fr4 with a cnc router over the pads - .012 holes for qfn and .026 for most other parts. After applying the paste I put the board in a fixture and drop another piece of fr4 that has cutouts for parts placement over it. I then just drop the parts into their places and pop it in the toaster. Works fine for me. Downside is that you need a cnc router to do it right.

Mark

-----Original Message-----

>From: DJ Delorie <dj@...>
>Sent: Jul 26, 2009 11:16 AM
>To: Homebrew_PCBs@yahoogroups.com
>Subject: Re: [Homebrew_PCBs] making surface mount boards
>
>
>Henry Liu <henryjliu@...> writes:
>> I was thinking about this and can't I just pre solder all the SMT tabs
>> then apply flux and the part on it then bake it or use a skillet?
>
>I don't think it will be sticky enough to hold all the parts in place
>as you move the board around.  Once you've soldered the pads, you have
>a hard bump that wants to move the part *away* from alignment, whereas
>solder paste can be flattened and is sticky to hold the parts in
>place.
>
>
>------------------------------------
>
>Be sure to visit the group home and check for new Links, Files, and Photos:
>http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>