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| Soldering BGAs -- solder paste or not? |
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| ebastler:
Following the helpful advice in an earlier thread, I have chosen a BGA package with 0.8 mm pitch and 15*15 balls for my first DIY board design with a BGA. (Actually a chip-scale package, Xilinx' CSG225, but I believe that does not make a difference?) I have completed my first cut at laying out the PCB. While I let that sit for a few days, I'm thinking ahead of how to populate the board. Just two prototypes for the time being, and maybe a very small "series" later. (Say a dozen or so, so manual labor is very much allowed.) So far I have hand-soldered the larger SMD packages I have worked with, via a soldering iron (drag soldering) or a cheap hot-air station. For the BGA, I was thinking about trying the "frying pan and sand" approach, which seems less stressful for the part than blasting it with hot air from above. First question: Good idea or not? My second question refers to the stencil I would need to order. The consensus seems to be that a BGA should be placed either in just a layer of tacky flux, relying on the solder balls that come with the package only, or in "a bit" of solder paster. But when I order a standard stencil based on the mask layer, the BGA pads would get just as much paste (per area) as the regular pads for parts which don't bring their own solder. Wouldn't that be too much solder, when combined with the balls? So what is the accepted approach here? A "customized" stencil with smaller openings for the BGA? No openings at all? Or just go ahead with the regular amount of solder paste and "she'll be alright"? Thanks for your advice! |
| jpanhalt:
I am getting into reflow for the first time, so take whatever I say with that in mind. I have done a bit of reading over the past 2 months, though. Of course, there are lots of videos and advice about BGA's on the Internet. Most of it seems to not use additional solder, but like all such advice,it is hard to evaluate the expertise of the giver. I looked for advice from manufacturers. PCBCart popped up first, and it also says additional solder is not usually needed (https://www.pcbcart.com/article/content/bga-packaging-technology.html ) There is probably advice from other manufacturers/assemblers. Finally, since my design was a first venture into reflow and current concerns with international shipping, I contacted OSHStencils in the US by email. It was quite helpful in terms of deciding aperture size and stencil thickness. I was also very happy with the turnaround time, price, and quality. Ordered late Thursday, shipped Saturday, received Monday. Of course, international shipping would be slower, particularly now. But I suspect OSHStencils would still respond to your question by email. Regards, John |
| cgroen:
I routinely solder BGA packages on boards here. I always use stencil (JLCPCB/PCBWAY/Aisler) and a ReflowR (hotplate). I use Chipquik TS391AX50 (T4 balls) from Mouser. (so using solderpaste for BGA in my case :) ) I have yet to have a single problem using this method! |
| SiliconWizard:
As a general thought, reflowing BGAs with just flux but no additional solder paste is more common for hand reflowing (with hot air for instance) from what I've seen and experienced, whereas for oven reflow (or similar - meaning reflowing the whole board), using solder paste is more common. I've rarely seen using stencils with no openings for BGA pads. |
| ebastler:
Thank you all for the helpful feedback! @jpanhalt -- OSHStencils looks like a good place. I did not have them on the radar; I was assuming that I'd order stencils from JLCPCB or whoever at the same time as the PCBs. But knowing that OSHStencils actually offer email support is a big plus -- not something I would take for granted given their pretty low cost. @cgroen -- any chance you tried a not-so-tightly temperature controlled hot plate before you got the ReflowR? Would you consider the automated temperature profiles of the ReflowR mainly a convenience (walk away while it's soldering), or do get get much better reproducibility? At 25 Euros a pop for the FPGA I will use, the ReflowR would quickly pay for itself if otherwise I have to discard every other soldering attempt and want to make a dozen boards... @SiliconWizard -- yes, upon further reading that seems to be the consensus: Using flux only is apparently mainly done in rework situations where you can't add solder paste in a controlled way, since you can't fit in and fixate a stencil. So, if applying solder paste, should it be the regular amount (covering the complete pad), or do people use smaller apertures for the BGA pads? |
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