Recently I designed a robotics “vision system” and ordered prototype PCBs and components (most of which has arrived). However, I haven’t been able to decide what is the best way to assemble prototype PCBs with lots of SMTs, including BGAs, QFNs, QFPs and resistors and capacitors in sizes 0805, 0603, 0402… and 0201 to bypass the GND and PWR pads underneath BGAs. The finest QFN pad-pitch and BGA ball-pitch is 0.50mm (with 0.25mm width pads).
The approaches I’ve considered are:
#1: http://www.aapcb.com - let someone else with pick-and-place assemble my PCBs.
#2: http://www.zeph.com/systems.htm - 3LMTZ-7-BGA system ($8000 ~ $10000).
#3: more-or-less manual assembly system including:
A: stereo microscope with dual boom stand - $500
B: PCB holder cradle to hold PCB above preheat - $200
C: stainless steel stencils for both of my PCBs - $200
D: vacuum-pen SMT pick-up tool to place SMT devices - $200
E: hot air pencil to solder discretes and parts with pins - $1000
F: hot-air heater to pre-heat PCB to 150C~210C for soldering - $750
G: hot air gun (plus selection of nozzles) to solder BGAs/QFNs - $200
H: high quality reflow oven (if necessary to achieve reliable quality) - $4500
I: miscellaneous other related devices, tools and supplies - $2000 plus or minus $1000
My nominal product choices for the above:
A: http://store.amscope.com/sm-4tz-80s.html
B: http://www.zeph.com/board.htm
C: http://www.quickstencil.com/prototype-stencil-kit.aspx
D: http://www.zeph.com/zt3web.htm
E: http://www.zeph.com/pencil.html
F: http://www.zeph.com/smdpreheater.htm
G: http://www.amazon.com/Aoyue-852A-Digital-Rework-Station/dp/B000HDDXY0
H: http://www.apsgold.com/reflow-ovens/low-volume/gf-b-ht-reflow-ovens
I: http://www.zeph.com/directory.htm
I’m looking for advice, especially from people with lots of SMT assembly experience. For sure, I wish I had $40,000 to buy a spiffy automatic pick-and-place machine with 4+ zone conveyor reflow oven… but alas, that’s $10K more than my entire budget for this entire project, including prototype PCBs, tooling for the die-cast aluminum cases, components (on the PCB), a 4-channel 5GSPS PC oscilloscope (picoscope 6403), and “all other expenses” (mostly A~H above). And yes, this is a personal project, but also yes, I’m planning to sell the results as a product when it is complete. So yes, this is “more than a typical hobby project”, but “funded by many years of frugal living and savings… and nothing remotely resembling a real commercial budget”.
The typical response to my questions so far has been “you bit off far more than you can chew”. No problem, that’s probably what they honestly think. But I’ve bitten off vastly more than I could chew on dozens of projects over the past 30 years, and I finished every single one, and sold or licensed most of them to companies, and they became real products. On the downsize, though I designed and prototyped dozens of fancy gizmos with large, sophisticated multi-layer PCBs back in the “dark ages”, I’ve been focused on software the past 15 years, and SMT has taken over everything during my “keyboard years” (for lack of a better term). So I have lots of general context and experience, but pretty much zero up-to-date PCB assembly experience. Hence my request for some considered opinions from those more up-to-date on prototype assembly with fine-pitch SMT.
In case it matters, the details of my PCBs are:
#1: the “eye” - 2.80" x 2.80" x 0.0625" - 6 layers - 50 components - prototype quantity 50
#2: the “quad” - 5.80" x 5.80" x 0.0625" - 8-layers - 300 components - prototype quantity 25
The PCB surfaces are ENIG (immersion gold).
Their minimum trace/space/via-size is 4-mils/4-mils/8-mils.
The PCBs adopt “fill-and-cap” to implement “via-in-pad” to make BGA routing/assembly easier.
All components are SMT except 40-pin ribbon-cable headers and RJ45/power/microphone-jacks.
The ID of every silkscreen box around every BGA and QFN part is exactly equal to the maximum OD of the BGA or QFN package it surrounds (to aid placement).
While the above PCB assembly techniques (and product choices) are the result of my searching and researching on the internet the past few weeks, maybe you have an entirely different approaches and equipment/devices/supplies/etc: I am happy to hear them. I need to keep my total budget for PCB assembly goodies under $10,000… and hopefully many/several thousand under that.
One specific question: Does anyone know from experience whether it is practical to solder fine-pitch BGAs and QFNs with these hot-air solder guns + nozzles… with the pre-heater below the PCB to pre-heat it to ~170C before soldering from above?
PS: I strongly resist option #1 above, even though that might be considered “the safe way”. Why? Because then I’ve “blown” my PCB assembly budget on a one-time “service” rather than equipment that will serve me well over the next 20 projects and ~50 PCBs I plan to develop over the next 3 to 5 years. Thus I think very much opposite most companies I’ve seen, who are happy to pay infinite sums for salaries, consultants and services… but refuse to spend anything for capital equipment to help make their employees productive!
So… what should I do? Which approach? What equipment/devices/supplies/etc?