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Old 05-13-2020, 04:21 AM   #1
myth77
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Default Noob - reballing, balling, stencil questions...

Ok, like i said in the title i am new in bga replacing so i have a several questions:

1. Stencils...on every stencil it is written a size of a balls to use for reballing..but are they always correct? yesterday i was reballing one pch, on stencil it was written 0,45 mm...but i would swear that on other working board the balls were little smaller...maybe 0,4 mm
2. Trapped moisture...i read a lot of times that after and before replacing bga chips that they should be pre-baked for 8 houers on 52C...to dry any possible traces of trapped moisture...I just read about it a few times...but never seen on the videos on youtube anyone mentioned it in the process?
3. After i used stencil and put the balls on the bga it is better to use a small preheater, turn it on 170C and then after it reaches that temperature to use a hot air gun from top to solder balls?
4. When placing a chip back to the board before reballing with station...i should put a very small amount of flux? I am seeing videos on youtube and they are all different...on one video the guy is putting high amount of flux...and in the others only little from top of his finger...?
5. I tried to solder one pch yesterday (first try) with soldering station.... and pch from dark green colour has gone to very very dark green colour almost black..
I was careful with the temperatures... the bottom was never above 180C and upper was maybe for 20 seconds arround 220 C to reball it on the board...

Thank for the answers..
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Old 05-13-2020, 04:47 AM   #2
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Default Re: Noob - reballing, balling, stencil questions...

1.) Not every stencil is 100% accurate on the size.
2.) Baking should be around 125c.
3.) I don't think there is a better way, just which ever way works, some like direct heat, others indirect or a bit of both. The less times the IC is subjected to reflow temperatures the better though.
4.) The differing amounts are perhaps down to different fluxes ? I use the smallest amount possible otherwise there is a chance the balls can wash away if there is too much.
5.) There will be some colour change, I suggest using two thermocouples on the top to help with the accuracy of your temperature, it shouldn't need that hot with lead free balls.
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Old 05-13-2020, 05:03 AM   #3
myth77
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Default Re: Noob - reballing, balling, stencil questions...

Thank you for the answers...just a few more

Quote:
Originally Posted by diif View Post
2.) Baking should be around 125c.
For how long?
Quote:
Originally Posted by diif View Post
3.) I don't think there is a better way, just which ever way works, some like direct heat, others indirect or a bit of both. The less times the IC is subjected to reflow temperatures the better though.
In my experience using only heatgun especially on large chips ends with balls moving on the chip before melting temeperature...but maybe i am doing something wrong.

Quote:
Originally Posted by diif View Post
5.) There will be some colour change, I suggest using two thermocouples on the top to help with the accuracy of your temperature, it shouldn't need that hot with lead free balls.
ok, thank you..so you sugest lower top temperature...205C for 20 seconds on the end of the process?
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Old 05-13-2020, 06:12 AM   #4
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Default Re: Noob - reballing, balling, stencil questions...

Quote:
In my experience using only heatgun especially on large chips ends with balls moving on the chip before melting temeperature...but maybe i am doing something wrong.
Are you using a heatgun or a hot air station? Are you removing the stencil before reflowing?
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Old 05-13-2020, 06:15 AM   #5
myth77
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Default Re: Noob - reballing, balling, stencil questions...

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Originally Posted by Spider1211 View Post
Are you using a heatgun or a hot air station? Are you removing the stencil before reflowing?
Yes i remove stencil before reflowing...and yes i use a heatgun but before that i preheat bga with small preheater to somewhere around 170C.

Last edited by myth77; 05-13-2020 at 06:17 AM..
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Old 05-13-2020, 06:19 AM   #6
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Default Re: Noob - reballing, balling, stencil questions...

Keep the stencils on and reduce the airflow. The stencil will help maintain the balls in place and lower airflow will avoid blowing the balls.
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Old 05-14-2020, 04:01 PM   #7
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Default Re: Noob - reballing, balling, stencil questions...

In my experience after reballing and removing the stencil, if you use the heatgun from above the tacky flux will liquify and the balls wander around and merge with each other no matter how low the airflow

I found better results heating the BGA from below

With some practice I have mastered desoldering the BGA without stripping PCB/BGA pads, but as much as I have tried, I have not yet mastered the method of resoldering the BGA once it is reballed (or soldering new ones) regardless of how much or little flux I use.

I think this is because i can't get proper heat transfer to the balls as they are only in slight contact with the PCB so the heat from the PCB preheater and lower air nozzle does not conduct to where it is needed.

I am now trying a different method of 'printing' solder paste onto the PCB using a stencil, then sticking the reballed BGA into the paste then heating. I don't know if that will actually solve my problem yet, I am awaiting some direct heat stencils and solder paste but just by understanding the basics of heat conduction it sounds reasonable that it would work.

Last edited by dicky96; 05-14-2020 at 04:05 PM..
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Old 05-16-2020, 09:11 AM   #8
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Default Re: Noob - reballing, balling, stencil questions...

Quote:
Originally Posted by dicky96 View Post
In my experience after reballing and removing the stencil, if you use the heat gun from above the tacky flux will liquify and the balls wander around and merge with each other no matter how low the airflow
Too much flux. If this is residue from flux after reballing, leaving the old flux on and then try to "reflow" the balls again it's definitely way too much flux. In BGA Reballing "less is more" definitely applies to flux use.
Also, if your balls attached to the pcb, why would you reflow them again ? Useless imo, unless some didn't align up well. What flux you use?
Quote:
Originally Posted by dicky96 View Post
I found better results heating the BGA from below
No matter what rework job you do, preheating will always help. I reball using DH stencils on a small preheater @200-230c and some HA on top in the final step (if needed) using a Quick 861DW @275c, airflow @40, no nozzle. Might have to lower airflow on smaller balls. (Btw, have a few jigs and NON DH stencils, but prefer the DH ones. Unless maybe if having to do to a specific type of BGA multiple time might setup a jig for it. Although, so used to DH stencils...)

Quote:
Originally Posted by dicky96 View Post
With some practice I have mastered desoldering the BGA without stripping PCB/BGA pads, but as much as I have tried, I have not yet mastered the method of resoldering the BGA once it is reballed (or soldering new ones) regardless of how much or little flux I use.
I think this is because i can't get proper heat transfer to the balls as they are only in slight contact with the PCB so the heat from the PCB preheater and lower air nozzle does not conduct to where it is needed.
If you have perfect lifts your profile should be +/- OK but might need a longer time or a degrees more. I presume that is a lead free lift?
When reballing, lead or lead free?
When soldering BGAs back, what temp (C) is your IR bottom heater set at?
Used top and bot HA profile? Used Ramp values?
Quote:
Originally Posted by dicky96 View Post
I am now trying a different method of 'printing' solder paste onto the PCB using a stencil, then sticking the reballed BGA into the paste then heating. I don't know if that will actually solve my problem yet, I am awaiting some direct heat stencils and solder paste but just by understanding the basics of heat conduction it sounds reasonable that it would work.
This will increase the risk for bad results soldering BGAs back. Risk for creating "Head in pillow" errors. Advise you not to.
If the stencils you ordered are the same DH stencils used for reballing will probably put too much solder paste on the pcb. If you'd heat it up might form a solder ball pretty close to the ones on the BGA itself.

Last edited by Deusjevoo; 05-16-2020 at 09:36 AM..
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Old 05-17-2020, 04:03 AM   #9
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Default Re: Noob - reballing, balling, stencil questions...

@Duesjevoo
Thanks for the reply. I have the same hot air station as you, though for bottom preheater I am using an improvised method witha Kada 853B hot air preheater, a square metal plate (about 20cm) sitting directly over the hot air vent and a themocouple so i can monitor the temperature of the plate. This seems to work well enough. Once tha balls melt I can finish with the Quick 861 as you say but when I tried using it without getting the balls to melt first, they just wander around. This is with 90mm stencil and jig to reball, not with DH stencils.

I tried using the same profile that desolders fine, and hotter ones, to resolder LGA 1151 sockets (new ones not reballed ones) but as of yet I just can't get them to solder properly and I have tried maybe a dozen times now.

Next I am going to try the method seen in the video on this thread...
https://www.badcaps.net/forum/showthread.php?t=84396

Though you suggest that won't work.

I have the same BGA station as in that video, or near as damn it, but with a different brand name - mines a LY G720

I'm waiting DH stencils at the moment, I only have 90mm ones and there is not enough flat space on the PCB to use that.


added
-------

Yes it is a lead free lift. I am not sure what the new LGA1151 are but looking at them i am pretty sure they are also lead free. Thinking about it the solder paste I have is leaded. I guess I need lead free paste to attempt the above method? Or would leaded paste just help to lower the overall melt temperature if used with lead free balls as it would amalgamate/alloy with them.- and also aid with heat conduction into the ball?

Last edited by dicky96; 05-17-2020 at 04:20 AM..
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Old 05-17-2020, 05:12 AM   #10
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Default Re: Noob - reballing, balling, stencil questions...

Quote:
Originally Posted by dicky96 View Post
Yes it is a lead free lift. I am not sure what the new LGA1151 are but looking at them i am pretty sure they are also lead free. Thinking about it the solder paste I have is leaded. I guess I need lead free paste to attempt the above method? Or would leaded paste just help to lower the overall melt temperature if used with lead free balls as it would amalgamate/alloy with them.- and also aid with heat conduction into the ball?
I don't think you can use leaded paste if you're using the existing pre solderered balls on the new socket. They are just going to squish out the paste which will become liqiudus way before the lead free balls.
The paste will squish out regardless of whether it's leaded or lead free, I don't think you can use the both at the same time.
The methods you've tried have they been with the shield on the socket on or off ?
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Old 05-17-2020, 08:20 AM   #11
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Default Re: Noob - reballing, balling, stencil questions...

((Corrected my name in the quotes, it's DEusjevoo, NOT DuEsjevoo (small detail, but for search function...))

Quote:
Originally Posted by dicky96 View Post
@Deusjevoo
Next I am going to try the method seen in the video on this thread...
https://www.badcaps.net/forum/showthread.php?t=84396
Though you suggest that won't work.
Not saying it won't work but a higher risk for head in pillow errors. (HIP is a weak point that can make temporary contact but fail later or fail from beginning)
This means the solder paste melts, solder of socket melts and they should flow into each other. However, sometimes it doesn't, the solder paste melts, solder ball sits in it on top, doesn't mix, cools down and you get a concave melted solder past fitting around the convex solder ball of the socket. The solder ball looks like a head sunken in a pillow, hence the term "Head in pillow". One of the possible problems that might pop up.
It's worth a try of course but if you can get it done using flux only later after knowing your machine/profiles better will be a safer option.

Quote:
Originally Posted by dicky96 View Post
@Deusjevoo
Next I am going to try the method seen in the video on this thread...
https://www.badcaps.net/forum/showthread.php?t=84396
I'm waiting DH stencils at the moment, I only have 90mm ones and there is not enough flat space on the PCB to use that.
Stencil in that video is not a direct heat reball stencil but a solder paste printing stencil, the cut out edges look more like: / \ You squeege the solder on top in it, it sticks to the pcb. Due to bottom openig beeing larger than the top one you can lift the stencil leaving the paste on the pcb.
DH stencils are thicker and have straight cut out flanks on the holes. Solder paste might get lifted when removing.

Quote:
Originally Posted by dicky96 View Post
@Deusjevoo
added
-------
Yes it is a lead free lift. I am not sure what the new LGA1151 are but looking at them i am pretty sure they are also lead free. Thinking about it the solder paste I have is leaded. I guess I need lead free paste to attempt the above method? Or would leaded paste just help to lower the overall melt temperature if used with lead free balls as it would amalgamate/alloy with them.- and also aid with heat conduction into the ball?
Maybe idd better to start with same solder alloy first. Can always switch later if needed.
Should check with supplier and ask what solder those sockets have. If it's SAC307 it needs a 10c higher solder temp. SAC307 is often used as it's cheaper than SAC305 but melts at 227 instead of 217c meaning your profile temp has to be higher too. (Just an optional thought and random example, there are other alloys too but as you have so many fails... Always good to know what they used on it)

Last edited by Deusjevoo; 05-17-2020 at 08:22 AM..
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Old 05-18-2020, 02:52 AM   #12
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Default Re: Noob - reballing, balling, stencil questions...

Thanks guys
And sorry I seem to have hijacked someone else's thread

@diff
I normally try with the shield on the socket otherwise the machine can't pick it up to position it. I did try on at least one occasion by manually placing the socket and soldering it with the shield missing. I did that by partially unscrewing the vacuum/sensor so the machine stops lowering the top nozzle when the extended sensor hits the capacitors in the centre hole of the LGA socket.

Either way the socket seems to stick firmly to the PCB but by checking continuity between pins in the socket that should be connected to Vcc or ground, I can see it is not soldered properly. If it then remove the replacement socket I can clearly see that some of the solder balls melted - usually near the outside edges - but most of the balls look intact, like they never melted during soldering or desoldering.

Obviously the profile is hot enough to cleanly lift the original and the replacement socket - so why those balls don't melt I don't know unless it is to do with heat conduction between the PCB and the balls

I found some 260C lead free solder paste - though that is even hotter than normal lead free. I can't seem to find any solder paste that is 217C like regular lead free solder.
https://www.aliexpress.com/item/4000...archweb201603_

@dEUsjevoo
Well that shows how little I know about stencils then! - I didn't know there were also solder paste stencils. As the one in the video didn't look like a 80mm or 90mm I was dumb enough to assume it must therefore be the other sort: direct heat.

Your explanation of the difference makes perfect sense, but quite where I can get solder paste stencils from I am not sure, nothing matches that seach parameter on Aliexpress which is where i normally look for stuff, and google didn't find anything specific to LGA1151 either.

I will contact the seller on Ali and ask what type of solder balls the LGA sockets have. I bought a box full of them (1151, 1150) from this seller
https://www.aliexpress.com/item/3292...27424c4d8Wmawx

And some AM4
https://www.aliexpress.com/item/3292...27424c4d8Wmawx



@all
I think best thing is for me to do some video of the whole process and then hopefully someone can tell me what I am doing wrong

Last edited by dicky96; 05-18-2020 at 03:06 AM..
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