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MicroZED

Started by John Larkin October 19, 2013
On Tue, 22 Oct 2013 15:48:31 +0100, John Devereux <john@devereux.me.uk> wrote:

>Lasse Langwadt Christensen <langwadt@fonz.dk> writes: > >> Den tirsdag den 22. oktober 2013 15.21.23 UTC+2 skrev John Devereux: > >[...] > >>> >>> >>> Thanks, I am talking about the initial soldering operation on a bare >>> >>> board. AFAICS I could just plonk the BGA down on its pads, without >>> >>> solder paste, with some flux. Heat everything up and the balls should >>> >>> melt and the package self-center. >>> >>> >>> >>> The point would be to avoid the initial stencil fee and full-up setup >>> >>> charges - and delays - when you just want to make a prototype unit. >>> >> >> you can get stencils that have the usual BGA sizes >> >> and many of the cheap chinese PCB prototype places now offer a stencil >> for something like 20$ > >Hi Lasse, > >Yes I saw those that JL posted. Still an extra cost, and need to make >sure I have in stock, and need to use solder paste which always goes off >by the time I need it etc. Although certainly it is an option especially >if I get my assembly house to do it (using their paste). > >But, is paste really essential for the process to work? Aren't the >solder balls already made out of - well - solder?
I've been told, by the owner of a professional assembly house, that you can do good hand placement or rework without paste. He says that, if the PCB pads are solder coated, rub liquid flux over all the pads *with your finger* (the finger part is apparently important), carefully place the BGA, and reflow. The new lead-free balls need high temp to reflow. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> writes:

> On Tue, 22 Oct 2013 15:48:31 +0100, John Devereux <john@devereux.me.uk> wrote: > >>Lasse Langwadt Christensen <langwadt@fonz.dk> writes: >> >>> Den tirsdag den 22. oktober 2013 15.21.23 UTC+2 skrev John Devereux: >> >>[...] >> >>>> >>>> >>>> Thanks, I am talking about the initial soldering operation on a bare >>>> >>>> board. AFAICS I could just plonk the BGA down on its pads, without >>>> >>>> solder paste, with some flux. Heat everything up and the balls should >>>> >>>> melt and the package self-center. >>>> >>>> >>>> >>>> The point would be to avoid the initial stencil fee and full-up setup >>>> >>>> charges - and delays - when you just want to make a prototype unit. >>>> >>> >>> you can get stencils that have the usual BGA sizes >>> >>> and many of the cheap chinese PCB prototype places now offer a stencil >>> for something like 20$ >> >>Hi Lasse, >> >>Yes I saw those that JL posted. Still an extra cost, and need to make >>sure I have in stock, and need to use solder paste which always goes off >>by the time I need it etc. Although certainly it is an option especially >>if I get my assembly house to do it (using their paste). >> >>But, is paste really essential for the process to work? Aren't the >>solder balls already made out of - well - solder? > > I've been told, by the owner of a professional assembly house, that you can do > good hand placement or rework without paste. He says that, if the PCB pads are > solder coated, rub liquid flux over all the pads *with your finger* (the finger > part is apparently important), carefully place the BGA, and reflow.
Thanks John. I suppose the *with your finger* bit helps to break through any film of contamination. Like they used to say to use a pencil eraser on bare copper / veroboard before soldering. For gold finish, do you think it is better to solder coat the pads first (give it some extra solder like the paste would) or just leave it alone (maximally flat surface).
> The new lead-free balls need high temp to reflow.
Yes that makes it a bit harder for this sort of thing. -- John Devereux
On Tue, 22 Oct 2013 07:38:58 -0700, Joerg <invalid@invalid.invalid> wrote:

>John Larkin wrote: >> On Mon, 21 Oct 2013 14:25:56 -0500, Jon Elson <jmelson@wustl.edu> >> wrote: >> >>> John Larkin wrote: >>> >>> >>>> We prefer BGAs to leaded parts. >>> OK, well, someday, I'm sure, I will be led kicking and screaming down >>> that path. The lack of ability to examine the solder balls worries me. >> >> The great thing about inspecting all those BGA balls is that you can't >> inspect them. >> > >That's why inspection is usually not done :-(
We do inspect the outer rows, but that's more a process feedback issue than individual board QC.
> > >> Actually, there are some optical gadgets that let you peek under the >> chip, from the side, and see the first 3 or 4 rows of balls fairly >> well. And you can see through the entire array, for debris and such. >> We just bought a good one for around $30K. >> > >Can it reliably detect flux residue somewhere in the middle? It's hard >to clean under a large BGA and then a few years down the road something >might quit working.
It can see down the rows pretty well, so it would see a clump of flux, or some stray solder balls. We use rosin flux, so we aren't concerned about leakage and corrosion, like you might be with water soluble fluxes. We've found BGAs to be extremely reliable, both initially and in the field, way better than fine-pitch leaded parts. And there's no other way to get 780 or 1120 pins on a chip.
> > >>> I do all my own assembly using an aging P&P machine and a modified >>> toaster oven. >> >> People do BGAs at home, too. >> >> These are cool: >> >> http://www.stencilsunlimited.com/bga_rework_stencils_stencilquik.php >> >> We use them for rework, but they would be good for hand assembly, too. >> > >How do you get the flux back out? Do you use Kester 951 flux?
We don't. Rosin flux residue doesn't do any harm.
> > >> I have overcome my fears of 1206s, 0805s, 0603s, SC70s and US8 >> packages (almost), TSSOPs, and BGAs. SC79s and 0402s still terrify me. >> > >Those are boulders. Some time around March next year I'll have to deal >with 01005. Not looking forward to that but as John Wayne said, man's >gotta do what man's gotta do.
Don't you ever get the feeling that playing with tiny parts on circuit boards isn't, well, a very macho way to make a living? Shouldn't we be out there chopping down trees or running ships aground or something? But on cold rainy days, I appreciate electronics more.
> >As I get older and SMT becomes smaller I have found that even the >Donegan 5x visor is sometimes not enough.
As the parts get smaller, everybody needs optics. Reconsider a Mantis. If you set the IPD knob to match your anatomy, they are comfortable and the view is stunning. And you don't have to hunch over like you do with a visor. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On Tue, 22 Oct 2013 10:48:09 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 10/22/2013 10:38 AM, Joerg wrote: >> John Larkin wrote: >>> On Mon, 21 Oct 2013 14:25:56 -0500, Jon Elson <jmelson@wustl.edu> >>> wrote: >>> >>>> John Larkin wrote: >>>> >>>> >>>>> We prefer BGAs to leaded parts. >>>> OK, well, someday, I'm sure, I will be led kicking and screaming down >>>> that path. The lack of ability to examine the solder balls worries me. >>> >>> The great thing about inspecting all those BGA balls is that you can't >>> inspect them. >>> >> >> That's why inspection is usually not done :-( >> >> >>> Actually, there are some optical gadgets that let you peek under the >>> chip, from the side, and see the first 3 or 4 rows of balls fairly >>> well. And you can see through the entire array, for debris and such. >>> We just bought a good one for around $30K. >>> >> >> Can it reliably detect flux residue somewhere in the middle? It's hard >> to clean under a large BGA and then a few years down the road something >> might quit working. >> >> >>>> I do all my own assembly using an aging P&P machine and a modified >>>> toaster oven. >>> >>> People do BGAs at home, too. >>> >>> These are cool: >>> >>> http://www.stencilsunlimited.com/bga_rework_stencils_stencilquik.php >>> >>> We use them for rework, but they would be good for hand assembly, too. >>> >> >> How do you get the flux back out? Do you use Kester 951 flux? >> >> >>> I have overcome my fears of 1206s, 0805s, 0603s, SC70s and US8 >>> packages (almost), TSSOPs, and BGAs. SC79s and 0402s still terrify me. >>> >> >> Those are boulders. Some time around March next year I'll have to deal >> with 01005. Not looking forward to that but as John Wayne said, man's >> gotta do what man's gotta do. >> >> As I get older and SMT becomes smaller I have found that even the >> Donegan 5x visor is sometimes not enough. >> > >Big BGAs need underfill to reduce the stress on the balls.
Would a thin layer of epoxy or whatever add any substantial strength to a thousand soldered balls? How would you get it in there? We've had zero ball-joint failures in the field, must be many billion ball-hours so far. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
John Larkin wrote:
> On Tue, 22 Oct 2013 07:38:58 -0700, Joerg <invalid@invalid.invalid> wrote: > >> John Larkin wrote: >>> On Mon, 21 Oct 2013 14:25:56 -0500, Jon Elson <jmelson@wustl.edu> >>> wrote: >>> >>>> John Larkin wrote: >>>>
[...]
>> >>> Actually, there are some optical gadgets that let you peek under the >>> chip, from the side, and see the first 3 or 4 rows of balls fairly >>> well. And you can see through the entire array, for debris and such. >>> We just bought a good one for around $30K. >>> >> Can it reliably detect flux residue somewhere in the middle? It's hard >> to clean under a large BGA and then a few years down the road something >> might quit working. > > It can see down the rows pretty well, so it would see a clump of flux, or some > stray solder balls. We use rosin flux, so we aren't concerned about leakage and > corrosion, like you might be with water soluble fluxes. > > We've found BGAs to be extremely reliable, both initially and in the field, way > better than fine-pitch leaded parts. And there's no other way to get 780 or 1120 > pins on a chip. >
BGA's fare a lot better in equipment that is mostly stationary. Less so where things move or vibrate a lot. But yeah, if you absolutely need many hundreds of connections there may be no choice.
>> >>>> I do all my own assembly using an aging P&P machine and a modified >>>> toaster oven. >>> People do BGAs at home, too. >>> >>> These are cool: >>> >>> http://www.stencilsunlimited.com/bga_rework_stencils_stencilquik.php >>> >>> We use them for rework, but they would be good for hand assembly, too. >>> >> How do you get the flux back out? Do you use Kester 951 flux? > > We don't. Rosin flux residue doesn't do any harm. >
I think that depends on the halides in there.
> >> >>> I have overcome my fears of 1206s, 0805s, 0603s, SC70s and US8 >>> packages (almost), TSSOPs, and BGAs. SC79s and 0402s still terrify me. >>> >> Those are boulders. Some time around March next year I'll have to deal >> with 01005. Not looking forward to that but as John Wayne said, man's >> gotta do what man's gotta do. > > Don't you ever get the feeling that playing with tiny parts on circuit boards > isn't, well, a very macho way to make a living? Shouldn't we be out there > chopping down trees or running ships aground or something? But on cold rainy > days, I appreciate electronics more. >
To compensate for that I just dusted off my old mountain bike and ride it after lunch. Those big tires feel very manly and make a manly noise on paved roads. The main reason is that I found that a brisk 30-45min walk every morning is not enough to keep the weight off. Seems the fuel efficiency of a human goes up with age.
>> As I get older and SMT becomes smaller I have found that even the >> Donegan 5x visor is sometimes not enough. > > As the parts get smaller, everybody needs optics. > > Reconsider a Mantis. If you set the IPD knob to match your anatomy, they are > comfortable and the view is stunning. And you don't have to hunch over like you > do with a visor. >
I don't have space for a Mantis here, mostly because I sometimes have very large prototypes on the lab bench. There can't be anything big and heavy in the way. When I want to avoid the hunch I use a Veho 20x USB microscope. A Supereyes 500x if it gets really small but that one doesn't allow several inches of vertical work space. Those are cheap "toy scopes" but they work quite well. As I said before, the good old days are today. -- Regards, Joerg http://www.analogconsultants.com/
On Mon, 21 Oct 2013 17:14:09 -0700, Joerg <invalid@invalid.invalid>
wrote:

>krw@attt.bizz wrote: >> On Mon, 21 Oct 2013 12:23:13 -0700, Joerg <invalid@invalid.invalid> >> wrote: >> >>> Jon Elson wrote: >>>> John Larkin wrote: >>>> >>>> >>>>> We prefer BGAs to leaded parts. >>>> OK, well, someday, I'm sure, I will be led kicking and screaming down >>>> that path. The lack of ability to examine the solder balls worries me. >>> >>> That's by far not the only thing that concerns me. >>> >>> http://www.cartoonstock.com/lowres/jfa2492l.jpg >> >> In all the places I've worked, we had the least trouble with BGAs. At >> the PPoE the big problems were QFNs that didn't wet on the sides. BGAs >> never had a problem, until they have to be replaced. ... > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > >And that's exactly the problem. They don't fail initially. But they can >later, on boards that are subject to lots of mechanical or thermal >stress. The thermal stress is often delivered by the BGA part itself. >There is a whole little industry that sprung up when BGAs were >introduced. People learned re-balling and other things and then repaired >game consoles, expensive laptops and such.
We have had very few fail, not enough to count. OTOH, we have a boatload of programmers who think that all serial ports are the same. It's no issue for the assembly houses to do, just that none of the engineering groups I've been in has invested the time or money to do it. They wouldn't get enough practice, anyway, perhaps because they don't fail often enough. ;-)
>> ... That never goes >> well locally. It's something that one has to do constantly to get >> right. We send it all out at the CPoE. > > >Smart choice. I am also a believer in sending stuff to the pros unless >you have real pros in-house. Trying to kludge it with BGAs just isn't >worth it. But I don't use BGA, I prefer parts with leads that can take >some stress. Leadless is ok if the part is very small, like the little DFN.
The boards and the parts are worth too much, particularly the engineering hardware. Production has all that stuff but they're in Mexico (add customs to the mix).
On Mon, 21 Oct 2013 16:53:52 -0700, John Larkin
<jlarkin@highlandtechnology.com> wrote:

>On Mon, 21 Oct 2013 14:25:56 -0500, Jon Elson <jmelson@wustl.edu> >wrote: > >>John Larkin wrote: >> >> >>> We prefer BGAs to leaded parts. >>OK, well, someday, I'm sure, I will be led kicking and screaming down >>that path. The lack of ability to examine the solder balls worries me. > >The great thing about inspecting all those BGA balls is that you can't >inspect them.
At the PPoE, we never needed to. There were never any problems. Here, we have X-ray gear but really little need for it.
>Actually, there are some optical gadgets that let you peek under the >chip, from the side, and see the first 3 or 4 rows of balls fairly >well. And you can see through the entire array, for debris and such. >We just bought a good one for around $30K. > >>I do all my own assembly using an aging P&P machine and a modified >>toaster oven. > >People do BGAs at home, too. > >These are cool: > >http://www.stencilsunlimited.com/bga_rework_stencils_stencilquik.php > >We use them for rework, but they would be good for hand assembly, too. > >I have overcome my fears of 1206s, 0805s, 0603s, SC70s and US8 >packages (almost), TSSOPs, and BGAs. SC79s and 0402s still terrify me.
We use all without fears. Unless there is a good reason to use larger, our default size is 0402. We try not to use BGAs with ball pitches less than .8mm but not because they can't be placed but for cost and reliability reasons. Lower than .8mm and the board dimensions have to change or B&B vias become necessary. They're also tough with 2oz. copper. ;-)
krw@attt.bizz wrote:
> On Mon, 21 Oct 2013 17:14:09 -0700, Joerg <invalid@invalid.invalid> > wrote: > >> krw@attt.bizz wrote:
[...]
>>> ... That never goes >>> well locally. It's something that one has to do constantly to get >>> right. We send it all out at the CPoE. >> >> Smart choice. I am also a believer in sending stuff to the pros unless >> you have real pros in-house. Trying to kludge it with BGAs just isn't >> worth it. But I don't use BGA, I prefer parts with leads that can take >> some stress. Leadless is ok if the part is very small, like the little DFN. > > The boards and the parts are worth too much, particularly the > engineering hardware. Production has all that stuff but they're in > Mexico (add customs to the mix). >
In the wake of all the BGA issues many service providers have sprung up. I don't know this place, just an example: http://www.etech-web.com/bga-rework-services.htm I just wish soemthing like this would be available somewhat locally for whole prototype assembly. A perfect biz opportunity for techs that were laid off. But hardly anyone does it. Beats me why not, considering that the investment costs in equipment are very modest. -- Regards, Joerg http://www.analogconsultants.com/
John Larkin wrote:


> I have overcome my fears of 1206s, 0805s, 0603s, SC70s and US8 > packages (almost), TSSOPs, and BGAs. SC79s and 0402s still terrify me.
It took me a while to get the hang of TSSOP, but now those are pretty much standard. I do automated placement and mass reflow of those with only a little trouble. I've stuck to 0805 passives, as there is not that much advantage to me to go smaller. (For microwave or high speed stuff, there may be electrical advantages, but I'm not in that regime.) I had a real bad experience with a chip-scale comparator (AD CMP603) that was only available in that package, had 65 on each board, and massive number of shorts under the chips. Soured me on the whole concept. Jon
On Tue, 22 Oct 2013 10:11:10 -0700, Joerg <invalid@invalid.invalid>
wrote:

>krw@attt.bizz wrote: >> On Mon, 21 Oct 2013 17:14:09 -0700, Joerg <invalid@invalid.invalid> >> wrote: >> >>> krw@attt.bizz wrote: > >[...] > > >>>> ... That never goes >>>> well locally. It's something that one has to do constantly to get >>>> right. We send it all out at the CPoE. >>> >>> Smart choice. I am also a believer in sending stuff to the pros unless >>> you have real pros in-house. Trying to kludge it with BGAs just isn't >>> worth it. But I don't use BGA, I prefer parts with leads that can take >>> some stress. Leadless is ok if the part is very small, like the little DFN. >> >> The boards and the parts are worth too much, particularly the >> engineering hardware. Production has all that stuff but they're in >> Mexico (add customs to the mix). >> > >In the wake of all the BGA issues many service providers have sprung up. >I don't know this place, just an example: > >http://www.etech-web.com/bga-rework-services.htm > >I just wish soemthing like this would be available somewhat locally for >whole prototype assembly. A perfect biz opportunity for techs that were >laid off. But hardly anyone does it. Beats me why not, considering that >the investment costs in equipment are very modest.
In a former life, my boss had a CM company. He got laid off during one of the downturns and bought some placement machines at a penny on the dollar and went into business. Made a bunch and then sold out. He's done similar things a couple of times.