First PCB Assembly Production Run

For those of you who have any interest in the tools and manufacturing side of things I present the fruit of my diy labor.

Those of you trying to work out from the pictures what the hell I'm making - it's a 3 way solenoid valve controller for a manual solder paste dispenser and vacuum pen device. (a shrink of: http://www.groupdiy.com/index.php?topic=45094.msg568212#msg568212)

(Once completed, Fully Assembled PCB's will be available from the Expat Audio store - the only extras you'll need are the pneumatic parts and a 12VDC power supply)



DSC_0387.JPG by ExpatAudioRochey, on Flickr

These boards were manufacturerd by the excellent seeed studio service, then I created a solder stencil and vacuum placed the resistors, caps and transistors. There's a little few more through hole components to be placed. Nothing too stressful.

The solder paste stencil was created using my CNC machine to drill small 0.9mm holes in the center of each pad. Details in this thread:
http://www.groupdiy.com/index.php?topic=46382.0

The Vacuum Pick and Place pen was created using the circuitry developed in this thread:
http://www.groupdiy.com/index.php?topic=45094.0


1. To start with, a jig was made to hold the pcb's to be stencil'd in place.
Zoom in on the original size image to see how much coverage there is between the stencil hole and the pad itself.

DSC_0384.JPG by ExpatAudioRochey, on Flickr

2. That allows multiple boards (in this case 10) to be stencil'd quickly.

DSC_0385.JPG by ExpatAudioRochey, on Flickr

3. Cut reels of components, and place in component holder, ready to manually vacuum pickplace over to boards!
The skillet was still cold at this point, and unpowered.
The "component holder" is a square of acrylic with 8mm wide, 2mm deep troughs running through it (done on my cnc). I cut the reels of components into 6" strips, tape them down in the grooves, then vacuum pick and place from them.

DSC_0386.JPG by ExpatAudioRochey, on Flickr

4. Manually pick place (no pictures for this... was busy picking and placing!

5.Fire up skillet and reflow (with a little help from a hot air gun from above
.... (again, no pics - was busy trying to get solder to reflow!)

6. Admire handywork and do some quality control.

DSC_0388.JPG by ExpatAudioRochey, on Flickr

All the boards looked great actually. it looks like just the right amount of solder was dispensed!

7. Solder Through Hole Parts (connectors)
TBD - Will Update

8. Basic solder test - apply power and stand back
TBD - Will update

9. Program host controller.
TBD - Code is mostly running on the prototype I built.

Looks great!

Can I ask how fast the fusion PCB service turnaround was? I just placed an order today and I'm hoping for a decent turnaround.

For contrast, a slightly different (and more traditional) take on this process:

http://www.flickr.com/photos/66148159@N03/sets/72157627392769082/

Six thousand RGB LEDs, >27000 parts in total, ten students/two coaches, two 13-hour days. Tools used were tweezers (vs Rochey's vacuum pump/nozzle) and a cheapo SMD oven (vs Rochey's skillet). To put things in context: building one of these by hand takes me ~4 hours straight, solder paste + unskilled (student) labor reduces that to three man-hours, pizza breaks included. A low/mid-range auto P&P machine would do 10-12 boards an hour (assuming no time wasted on changing feeds), which would make my sweat shop only three times as slow.

The result: a fully programmable light sensitive LED wall.

http://www.flickr.com/photos/66148159@N03/6064800354/in/set-72157627350373511/
http://www.youtube.com/watch?v=FUgrNJNWhH
http://www.youtube.com/watch?v=f3G29F9JI8g

JD '6k RGB LEDs = 250A@5V max' B.

Is the square of acrylic that you use as a component holder anti-static?

Do you pick the part up right from the cut tape or handle them?

For most parts this probably doesn't matter.. but if you pick right from tape carrier that should be cool.

JR

PS I've found that when you have a lot of these to do you can pay companies that specialize in doing this.  8)

JohnRoberts said:

Is the square of acrylic that you use as a component holder anti-static?

Do you pick the part up right from the cut tape or handle them?

For most parts this probably doesn't matter.. but if you pick right from tape carrier that should be cool.

JR

PS I've found that when you have a lot of these to do you can pay companies that specialize in doing this.  8)

Click to expand...

Oooooh - some really good points there John.

I hadn't really considered it - as I was mainly placing passives (with the occasional PN2222 transistor).
I was lifting directly from the tape, but I occasionally had to rotate a part by putting it down on the plastic and rotating it.

Do you think that a tape holder made of wood would be less of a static risk? (more of a dust risk I guess...)

P.S. Companies that specialize in this often charge a lot of money in setup fees. When your doing runs of 10 or 20... that gets expensive pretty fast!

If the part is small, aluminum is an obvious static avoider.

perhaps some modern composite that is slightly conductive.

Yup, small qty runs are not production friendly. Most CMs only have two speeds full production, and slow expensive hand assy reserved for rework.

In the future we may see some specialized machinery where say a glorified inkjet printer prints solder paste onto a PCB for softer low volume production. There is no reason why this couldn't be machine controlled, except for relatively large machine time VS screening it through a stencil. 
====
This larger volume efficient run quantity is why I went through so many revision levels on my current re-design with several painful hand built prototypes to get the design right before I have hundreds of them to rework....  In a bit of good luck I caught one mistake after I released the design to production, but luckily before my CM had started work, so I could slip in one more revision change after the clock struck midnight...

The next mistake I find will mean reworks by me... but I feel lucky..for now. (fingers crossed).  :

JR

John -- I think I could make a component holder out of copper pcb plate.

The pits (which the tape would lay in) wouldn't have copper, but there would be copper to the left and to the right of them. If components slip/fall out of the tape on to the holder, then they'll land on some lovely conductive copper (tied to ground)

Ideally, I'd mill some aluminum. But I heavily suspect that my little CNC machine isn't up to the task.

What do you think?

Definitely some conduction is good for ESD considerations, but pure metal conduction can be a part killer... it is really the RAPID discharge of static electricity that can render components zapped... although "walking dead" is another possibility where the component prematurely fails, but passes initial QA tests and is even shipped to the customer; it was kinda zapped, but still functional...  Slower discharge bleed is better...  Don't have to be HBM Class 0 compliant to get there

An ionizer would be handy for plastic in the ESD workspace as they provide ions (both + and - ) that can remove static charge on insulators (including paper)...  They have wear parts where the electrodes will lose their sharpness and thusly the voltage gradient around the tip decreases and less ions... most models have a beeper that will note when they tips/electrodes  need to be replaced...  There is new research that some ion content can scar lung tissue over time however...

Used to have a CM for a previous employer, that would wrap aluminum foil around insulation foam "blue board" from the local home improvement centre as part of their ESD policy to carry PCBs and components around (with many pin holes pricked through the foil into the static generating insulation; they quoted me that their floor is ESD safe with a coating therefore there should be no issue!!!); the CM was in service before I came aboard and I protested their policies to the employer... we had walking dead (although hard to prove, perhaps, but c'mon....)  They're out of business now; and so is the employer...  The CM real estate is now a doggy daycare - it literally went to the dogs....

Really cool build indeed....  Cheers....

Copper seem satisfactorily conductive. When I had a DIY ground plane under my workbench I connected it to real ground through a couple Meg ohm resistor (I guess industrial safety would want it hard bonded to ground to take out mains fuses, I was more concerned about reducing hum pick-up for my kluged prototypes that looked like some space spiders creation from hell. And for your app static is a high impedance, low current phenomenon. 

While static is not much of problem here in MS, back when I was working in CT we used to have a shop vacuum that doubled as a van de graf generator... vacuuming out my office would leave me dangerously charged to way too many volts. I ended up wiring a couple meg resistor to the light switch plate screw for my office so I could painlessly discharge my meat capacitor.  I never figured out completely why taking a pee didn't also discharge my capacitor, but apparently the water in the bowl is not grounded to earth. 

I was talking with an IC design guy the other day and he was complaining about how they have to put full ESD protection on every IC pin these days. Customers just don't understand doa parts, even when they are responsible for the fault.

JR

The bowl with the charged dialysis could make a Leyden jar capacitor application (just need another electrode)....  The bowl is isolated (and is a dielectric) where the trap in the ceramic does not make contact with earth until the long end of the run of PVC (unless a cast iron stack) during a flushing event....  Then the filter response could be calculated in true "wave lengths"  

Meat capacitors do indeed tend to be leaky of course....

The only concern after working in Class 0 ESD environments is that if one had a PCB that had +3kV of static charge on the left side and -2kV of static charge on the right side, and placed it on a metal substrate with very good conduction...zap 5kV....  The anti static mats are ideal with the distributed slight conductance to bleed charges locally, but the metal underneath for "shielding" would be an excellent idea, especially for audio...

We couldn't use ESD protection on any of our pins in the GaAs microchips we were designing, because of the RF implications with stray diode capacitance bummer... Saw some ESD zap through under the microscope when we were in a rush...

gemini86 said:

Looks great!

Can I ask how fast the fusion PCB service turnaround was? I just placed an order today and I'm hoping for a decent turnaround.

Click to expand...

i think it took about 3 weeks to get here.

amazing service though. ideal for prototypes.

Also - note that following this discussion, I've decided that it's about time that I ESD protect my workstation at home.

Apparently, not all that difficult. I already have the ESD mats, but they aren't currently connected to ground.

Interesting Q for those of you who might know -- should the connection to ground be direct, or through a MEg-Ohm interface?
There seems to be a lot of conflicting data points:

Per ESD 6.1 "Provisions may be made to include a resistor where it may be required for a purpose other than ESD."

ESD Handbook TR 20.20 paragraph 5.1.3 Basic Grounding Requirements "The first step in ensuring that everything in an EPA is at the same electrical potential is to ground all conductive components of the work area (worksurfaces, people, equipment, etc.) to the same electrical ground point. This point is called the common point ground. The next step in completing the ground circuit is to connect the common point ground to the equipment ground (third wire, green)"

One Megohm resistor is required in wrist straps, however, the recommended practice is hard ground per ANSI/EOS/ESD S6.1 that is no resistor between the common point ground terminal and a worksurface floor mat, or shelving. Per ANSI/ESD S20.20 Table 1 Grounding System Technical Requirement, the Recommended Range is less than 1 ohm AC impedance.

Most esd mats AFAIK are not very low impedance themselves so probably an academic question.

There is always an argument wrt safety, whether a solid ground path is a shock risk, or safety feature. Over the years I have blown up way too many parts with scope probe ground clips accidentally touching stuff to have an aversion to low impedance grounds around test benches. For assembling product the main concern is transferring charge or rapidly discharging charged capacitances. 

I can imagine arguments for all possible ways.

My personal preference is through a series impedance, but opinions may vary.  it doesn't take much conductance to prevent static.

Equipment chassis need robust grounds (IMO), for workers and bench setups not so much (IMO).

JR

PS: For extra credit how many mA are required to stop our heart?