I’m not sure my questions are appropriate to this group or forum, but that’s okay… just ignore this post if it’s out of line. I’ve been designing a “vision system” which is ultimately is supposed to be part of an insanely advanced “robotics” application, but is also perfect for many other applications. In essence, its just a moderately high-resolution digital video/still camera with controller that spews the images out to an attached PC via standard gigabit ethernet via standard RJ45 jack/cable. Well, its a bit stranger than that actually, because the image-sensor PCB (which I call an “eye”) is extremely simple, but up to 4 of these can be connected to the controller PCB (which I call the “quad”) so the controller can capture and forward 4 image streams to the PCB over the one gigabit ethernet connection.
Anyway, none of the above is relevant to my questions — except maybe to entice someone to answer my real questions, which follow.
I designed and prototyped dozens of digital devices and products [more than] several years ago, so all the components were standard DIP packages with 0.100" centers (plus non-SMT resistors, capacitors, etc). After several years of science, engineering and software (mostly), I return to design more hardware devices and find… MUCH has changed.
Most important, SMT (surface mount technology) is totally mainstream. In fact, 90% of the circuits I want to design with are only SMT. So all those years of prototype experience is now ancient… and obsolete.
Anyway, I finished the schematics and PCB-layouts for these two PCBs. and emailed the gerber files off to get prototypes PCBs made. Now I need to buy whatever tools, supplies and equipment is necessary to build these prototypes. To abuse myself further, I chose lead-free components and assembly, since that too seems the modern way.
What I’d like to know is, “what assembly/soldering techniques should I adopt, and what tools, supplies and equipment must I buy to build these prototypes?”. Specify brands and product numbers too, if feasible. I’m not starting a PCB assembly biz, and don’t have $50,000 to spend, but these do need to be reliable and of commercial quality… because hopefully they will become commercial products once all is finished.
Now I’ll try to describe the types of components on the PCBs, since that information is probably necessary to make informed suggestions.
PCB #1: the “eye” : 2.80" square, 0.0625" thick, 6-layers
PCB #2: the “quad” : 5.80" square, 0.0625" thick, 8-layers
Both PCBs have components on both sides. Except for 40-pin headers to connect to ribbon cables, and a very few other oddball components, ALL the components are SMT.
The PCBs have 4-mil trace/space widths, 8-mil holes, and all "normal"
characteristics (soldermasks and silkscreens on both sides, and 0.125"
holes in all 4 corners of both PCBs). All the internal layers are GND and PWR (various voltages), except one more signal layer on the quad.
The PCBs contain several BGA components (with 48, 56, 96, 256 balls), several QFN components (with 8 to 48 pads), several QFP components (with 100 to 128 pins), and several SOIC, SO8 and similar components. Most resistors are 0402, and most capacitors are 0603 (but a couple dozen are 0402 and 0201).
The smallest pad-to-pad (or ball-to-ball) “pitch” on the BGA and QFN packages is 0.500mm or about 20-mils (0.020"). I didn’t really grasp how small and close those pads and balls were until I received samples of some of these components! The first little box I opened (max8717) was in a 28-pad QFN package. At first, I thought the box was empty. Then I noticed these tiny little square flecks of black plastic in the corner of the box, and took one out to see what it was. Then I noticed the other side had a bunch of tiny silver pads around the outside! Yikes! That’s what happens when you work on PCB layout software at typical magnifications of 3200% to 10000% — you have no freaking idea how tiny are those pads, balls and pitches! AARG.
But that’s the way it is today, and I need to install and solder the components on these PCBs… and end up with solid, reliable PCBs. I’ve watched a number of videos on the internet, but almost all of them seem vastly too crude for me (soldering on a skillet or $25 convection oven) or vastly too expensive ($50,000 pick and place machines and so forth).
There MUST be an intermediate way! Please say yes! And describe.
I did run across a few possible clues and ideas (at least I think so).
First, it looks like $100 will buy me a “stainless steel stencil” to
help me apply consistent blobs of lead-free solderpaste on each pad. I’m not sure whether I need one stencil per PCB side, one stencil for both sides of a PCB, or whether I can buy one stencil with patterns for both sides of both PCBs on it. Any comments about this approach?
Second, it appears some low-end “reflow ovens” exist in the price range from about $500 to $2500. For the life of me, I can’t understand why a simple $50 convection oven plus thermistors and (air-mixing) fans plus temperature controller should cost more than $250, but what do I know? Is this a reasonable approach? Are these reliable? Do they support PCBs with components on both sides? Do I reflow each side separately?
Third, maybe an alternative to “reflow ovens” is “hot-air solder guns”? I’ve seen some pretty nice demonstrations on youtube of soldering small components with these devices. However, I can’t see how to solder in BGA and QFN packages with these devices… and I have BGAs and QFNs. These look great for removing and replacing misplaced components after a PCB is totally finished (by reflow oven probably), and maybe even soldering in most components with exposed leads (QFPs, SOICs, etc), but not BGAs or QFNs. Or is my imagination too limited in this case?
Fourth, I saw some advice on the internet that claimed assembling PCBs like these require a “manual (or automatic) pick-and-place machine”. After seeing a video of one of these in action on youtube, I can’t see how it helps aid placement accuracy AT ALL, though it might help keep the operator from getting sore arms quite as quickly… or maybe not. To be sure, automatic pick-and-place machines are massively “cool”, but vastly too expensive for me (looks like $12,000 to $50,000 to me).
I also saw a device called a “solder mill” at zeph.com, which could work for placing and soldering BGAs and maybe QFNs one-by-one… but leaves everything else to manual hot-air pencil soldering. This is also rather expensive… about $8000 for a complete system and kit, PLUS individual “templates and nozzles” for each BGA and QFN package at $450 per package type! Ouch!
But I’m looking for YOUR advice, especially from anyone who has gone through this (at home or work). And hey, if you have some of these gizmos in your garage (in or near Nevada), well… let me know!
So, all you electronics wizards… BRING ME UP TO SPEED !!! Thanks!