connected to the main display that needed
animation, as well.
I created a QuickStart shield that is actually a
collection of simple circuits:
• Four medium current low side drivers
• Two low current push-pull drivers
• An I/O point with 3.3V to 5V translation
• A microSD socket
To be honest, none of these circuits are
remarkable — they just happen to work well together
for this project, and some things I anticipate doing
down the road.
After double-, triple-, and quadruple-checking
everything, I exported the Gerber files for my shield
(called the QuickStart LED Driver) and sent them off
to Gold Phoenix PCB. I wanted blue solder mask to
match the QuickStart and paid an extra $20 for it. It's
a good deal. For about $140, I got 25 PCBs. Yes,
there are a couple of steps when using Gold Phoenix, but
it's really hard to argue with the price and quality.
I have two friends (Rick and John) that have the TOB-
155 toaster oven. Rick lives close and said I could borrow
his oven any time. John lives on the other side of the
country but solders a lot of surface-mount PCBs in his
oven, hence I wanted to turn to his experience.
My writing is typically about how to code, not how to
build — so this is a little different. I'm going to explain the
steps to fabricating my QuickStart LED Driver. These steps
are based on talking with those that have far more
experience than me. In the end, the process was easier
than I expected, and I was able to produce very nice
boards. Here we go.
Step 1 is to clean the PCBs with 99% alcohol (don't
use rubbing alcohol). Dirt and grease are bad — always.
Figure 8 shows my cleaned boards, ready for paste. BTW,
I picked up some nifty parts trays at All Electronics
for less than a dollar each. They're anti-static and
have a lip around all the edges which help keep
small parts from wandering away.
Step 2 is to apply the solder paste. John gets
stencils made and goes that route. This PCB was
my first attempt at SMD production and I was
trying to keep things simple. To that end, I ordered
a syringe of paste from Zephyrtronics. By using a
light touch with the syringe, under good light and
with a magnifier in the other hand, I was able to
place the paste pretty quickly. Keep in mind that
you don't need a lot of paste on a pad, and it's
best to keep things as neat as you can during the
process. Just as you wipe the tip of a soldering
iron to keep it clean, I found it best to wipe the tip
of the syringe from time to time to keep solder
paste going where I wanted it to go.
In Figure 9, you can see my reasonably neat
■ FIGURE 8. Ready for paste.
little solder paste blobs on the pads. Remember, solder
paste is a combination of flux and solder — there's not as
much solder there as you think.
Step 3 is to place the parts. Another useful find at All
Electronics was a pair of wickedly sharp tweezers; these
are perfect for the job. Again, I did my best to keep things
neat — there's no sense smearing paste around that could
form bridges between legs on an IC. Figure 10 shows
parts set carefully into the paste.
Yes, it does look like bridges are going to form
between the legs; they usually don't unless there's just too
much paste. On this board, I did have one small bridge
which was easily corrected with a fine-tip soldering iron,
but it was not in the area of the photo.
Step 4 is to check and adjust parts alignment. I use a
Step 5 is to bake the boards. Again, my friend John
May 2013 17
22 µF Digi-Key PCE3953CT-ND
0.1 µF Digi-Key 490-1726-1-ND
1N4001 Digi-Key 1N4001DICT-ND
BSS123 Digi-Key BSS123NCT-ND
FDS6612A Digi-Key FDS6612ACT-ND
10K Digi-Key P10.0KCCT-ND
25. 5 Digi-Key P25.5CCT-ND
DM3D-SF D Digi-Key HR1941CT-ND
0.2" x 2 Digi-Key 277-1247-ND
TC4427 Digi-Key TC4427ACOA713CT-ND
LM1084IS- 5.0 Digi-Key LM1084ISX- 5.0/NOPBCT-ND
0.1" M HDR Digi-Key S1012E-36-ND