MacBook 2141 problem with reballing a video chip

[PITERPENY]

I encountered a problem with reballing a video chip. Tell me what I'm doing wrong that sometimes the balls don't form as they should? Bottom heating 240C, top 320C, I pour flux well. And the result is this. Any advice is important.

[mon2]

Check the many videos on YT for ideas.

Use fresh and better solder paste. We use KOKI paste for our SMT line and build volumes of PCBs without issues (QFP / SOIC / BGA / WLCSP packages - no issues). If your paste is fresh (store in the fridge but mix it well before use and at room temperature - you can take some out the night before use) - you will not need to add flux.

We use KOKI S3X58-HF1100-3.

[PITERPENY]

I use paste only on small chips, maximum T2. But on CPU and GPU I use balls. With solder paste they are not perfect, unlike balls. But sometimes this happens when they do not sit down and I wonder why?! Usually you have to remove everything and do it again several times, which is very annoying.
and by the way, my pastes dry out quickly in the packaging. How can I return them to a paste-like state?

[mon2]

We store the solder paste inside our bar fridge after it is tightly air sealed in the vendor's jar. This allows us to use the paste even month later. We have tested many different brands of solder paste and highly recommend KOKI (Japan). If you zoom in on the paste, they are micro spheres of solder balls. Respectively, you must mix the paste well into a creamy texture before use. We have a SMD printer which helps us to automate most of the process -> bare PCB is shuttled in; board is auto-aligned -> stencil is kissed with the PCB after alignment -> squeegee blade applies the solder paste across the bare PCB -> process is repeated with the next board. We do have an automated solder jar mixer machine (~$1k USD from Asia - about $15k locally in Canada). We mix the paste for about 30 mins before use after taking out of the fridge. Do not store the used paste back into the original jar. Just not worth it. Use fresh paste every time.

Review the YT videos on using a direct heat stencil with solder paste to ball your own. While we have the many different sizes of solder balls, have yet to use the tools at our place. We do have a pile of ball-less BGA / WLCSP packaged ICs that need attention. Also, be sure the sphere is the proper size for your BGA package. The balls look a bit small for the pad on the IC. You can also google to review what others are using.

I do believe that you need to pre-flux the flat BGA pads before using the solder balls with a stencil. Be sure that the stencil aperture opening is large enough that the stencil can be removed after the solder ball has melted onto the pad(s). I think you just need more practice to perfect the process.

[PITERPENY]

Thanks for the informative answer. 80% of the time they always turn out great but sometimes it's just a nightmare. I use 0.45 ball size which seems like a great size to me. Of course it's easier to apply with paste but they are smaller and not all the same size which I don't like a bit. And yes I use direct heating stencils.

[TuanTongbadcaps]

Thanks for the informative answer. 80% of the time they always turn out great but sometimes it's just a nightmare. I use 0.45 ball size which seems like a great size to me. Of course it's easier to apply with paste but they are smaller and not all the same size which I don't like a bit. And yes I use direct heating stencils.

My advice is that you should apply a very thin layer of solder flux to the chip surface before pouring the ball. As for what appears in the photo, I would add a layer of more flux once the balls have bonded from the 1st heat and continue with the 2nd heat.