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Author Topic: BGA Soldering  (Read 4633 times)
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j2mb
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« on: April 15, 2014, 11:40:06 23:40 »

Hi,

I want to soldering BGA components in home. But I don't know what is the best way to do that. Is the reflow oven (like sold on ebay) a good choice? My budget is very low. I have a  hot air station but i don't know if is possible obtain a good results with that.
Please give me your feedback.

Sorry my bad English.

Thank you.

j2mb
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FriskyFerretReloaded2
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« Reply #1 on: April 16, 2014, 12:38:15 00:38 »

A talented tech can rework BGA without a fancy video camera BGA rework station. You need experience, a damn good solder paste like Kester EP256, and a metal paste stencil (not the plastic film type.) The PCB must be lightly preheated from behind. You can do this with your air pen. Not too much pre-heat or you will dry out and activate your solder paste. During reflow you'll want to heat around the component to let the heat soak underneath, sideways through the PCB material, as well as heating the component directly. You need to get the reflow done promptly once you start and not futz around slowly adding more and more heat. Once the flux activates in the paste, the paste must continue to liquidus quickly and smoothly or you'll end up with un-coalesced paste that will never reflow.

Don't worry too much about setting the air temperature to some exact, magical number. The amount of heat that is transferred to the PCB and component is largely controlled by the distance of the pen nozzle from workpiece. In skilled manual rework, experience is the key. You just have to practice and learn.

An oven would probably be better for you. The Chinese ovens on eBay are all crap. They're just sheet metal boxes with a heater and decals on them, built to look like reflow ovens, not real reflow ovens. They're scams to get your money. You're better off buying a used toaster oven. Contrary to widely accepted belief, you do not need a temperature controller that will run a precise temperature profile. In the old days, with finicky solder paste, a good profile and a nitrogen gas purge was needed. Nowadays with pastes like Kester EP256 and simple surface mount jobs, you can reflow a board in an electric fry skillet as long as it has a temperature control. Not recommended but possible.

Have a look here: http://rayshobby.net/?p=1246





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Parmin
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« Reply #2 on: April 16, 2014, 01:21:16 01:21 »

Over the years I found that the real secret of BGA hand soldering is to get the correct sized solder balls and screen.

Solder paste are good only if you have used and understand their properties.
Often the solder particles and the flux separates after a while in storage, and on application some pads would get more solder and the other would get more flux.
This in effect would give you less than uniform quantity of solder on the pads and would make it really difficult to achieve uniform height of solder "feet" protrusion.
You want the solder protrude uniformly so when reflow they would wet and connect pads in uniformly.

Using solder balls, you would start with uniform quantity of solders, and using a good fitting screen would make your application much easier.

Personally I use IR reflow in the lab, and hot air reflow in the field.
I have not used frying skillet, but I have used bottom heater when using IR reflow.
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« Reply #3 on: April 16, 2014, 11:26:10 11:26 »

Over the years I found that the real secret of BGA hand soldering is to get the correct sized solder balls and screen.

Solder paste are good only if you have used and understand their properties.
Often the solder particles and the flux separates after a while in storage, and on application some pads would get more solder and the other would get more flux.
This in effect would give you less than uniform quantity of solder on the pads and would make it really difficult to achieve uniform height of solder "feet" protrusion.
You want the solder protrude uniformly so when reflow they would wet and connect pads in uniformly.

Using solder balls, you would start with uniform quantity of solders, and using a good fitting screen would make your application much easier.

Personally I use IR reflow in the lab, and hot air reflow in the field.
I have not used frying skillet, but I have used bottom heater when using IR reflow.
Going back a few years. It could be a problem that many commercial available premade solder balls were very uneaven in size. Is this still a problem?
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Parmin
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« Reply #4 on: April 17, 2014, 12:36:22 00:36 »

Yes a while ago premade balls are made very rough indeed, but for the past 10 years or so this no longer an issue.
Ever since the mobile phone repair industry taken up worldwide, BGA reflow is now a daily occurrence for repair industry, thus the ball quality and size uniformity has become much much better.

Viz, the "Old" way of making the balls are by dripping then mesh, the new way of making the balls are by cut, roll then mesh.
By cutting lead off wire improve the uniformity of the product a lot.

You can now get BGA balls in mesh grid granularity down to 0.05mm and good brand balls usually guaranteed to be uniform to 1% in diameter.
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CocaCola
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« Reply #5 on: April 17, 2014, 05:14:34 05:14 »

As said above I highly recommend a toaster over over the skillet... I have used (and will continue to use) a $20 toaster oven for reflowing at home...  I have even done small production runs of up to 1000 units using said small toaster oven...

Also as said above there is certainly a 'proper' reflow cycle that the solder paste manufactures all recommend but I have never adhered to it at home and can't say that I have experienced any ill effects...

My reflow with a toaster oven goes something like this, fine adjustments based on any particular board need to be made if you are doing a run...  I place a slab of marble (marble tile) on top of toaster oven, this acts as a cool down area above room temp...  Preheat toaster over to 300 F, place boards in oven, close door and let sit for about 5 minutes to soften the flux and get it ready, crank heat full tilt and visually watch the paste and components, when the last component reflows wait 1-2 minutes more then turn the temp dial back to 300 F and let sit for 5-10 minutes...  Remove boards carefully and place on the marble cool down plate on top of the oven, this will allow the boards to more slowly cool down vs shocking the board...

BTW I have used top of the line solder paste but I generally just use the cheap stuff in small snap cap containers out of China as I have found it actually works quite well and it's generally pretty fresh and stays fresh since it's a small container that gets used up quickly...  If I need to I hit up any older paste with some no clean BGA flux and stir and in many cases milk a few more uses out of the old paste...  Do note that there are lots of bad and even counterfeit solder and fluxes coming out of China, know your supplier and product before you actually commit to any brand paste/flux for a job...

I have used Kynar screens and metal screens both work fine for most components but metal is better for some components like BGA as it leaves a heavier coating of paste behind...  BTW I can easily get 500 passes on a Kynar screen without a failure and that makes them very cost effective for small runs, I know a lot of people hate 'plastic' screens but I'm sold on them for small runs, especially when some of the guys cutting them will make me multiple boards for one flat fee as long as I panel the Gerbers myself with proper (2" or so) spacing between boards...

One last word the above is of course 'hobbyist' level or 'it needs to get done level' advice, if you are doing work for a company or client that expects industry standards to be followed, well follow them Smiley
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« Reply #6 on: April 17, 2014, 10:45:28 22:45 »

I have a  hot air station but i don't know if is possible obtain a good results with that.

In reply to this, yes it's possible to rework BGA with a hot air station, when I was doing in factory assembly line repair work for a major electronics manufacture I did all the repairs including BGA repairs with just a hot air rework station and soldering iron, but there is a steep learning curve to get good at it and I don't recommend it be the primary choice, ovens and stencils work much better...  In that factory environment it was cost effective to have me make the quick attempts at repair with basic tools and if it didn't work they just scrapped the board, each board was only allowed two repair cycles before it was deemed worthless and sent to the guy with a drill press that punched multiple holes in the board and tossed it into a recycle bin...  Also in that environment any 'micro' removed from the board for rework was tossed and a new one used in it's place to reduce failures due to overheating, the only exception was quick reflows if it was obvious that it didn't reflow properly...   In the OEM manufacturing environment labor quickly out cost component cost, so rework and repairs are dealt with differently then they are in the hobbyist arena...
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« Reply #7 on: April 18, 2014, 12:33:13 00:33 »

Hi,

Thank you very much for sharing your experience with me. I never try use a toaster for smd soldering but I saw a lot of people on the internet that use that. I go buy it for me and make a couple of tests folloing yours advices. Then I post here my results.

Thank you again.

PS: I will forget of the ebay ovens. I almost buy it one for me.  Wink

j2mb
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« Reply #8 on: April 18, 2014, 04:30:45 04:30 »

PS: I will forget of the ebay ovens. I almost buy it one for me.  Wink

I too had considered one, but after a lot of Googling discovered that many of them are far from what is advertised...  From broken crumbling slabs of plaster of paris for insulation, or no insulation to a micro and LCD that pretends to be doing a heat profile and offer temperature adjustments all the while the unit lacks any temperature sensing circuit so any settings and profiles are hogwash and at best just fake on/off profiles that might vary the temperature but probably are useless in the end...  And even then I had considered getting one to gut and rebuild properly since they are not that overly costly, but decided I would give the cheap $20 toaster oven a try and I never looked back or gave the Chinese reflow ovens another look...

BTW I did try the skillet method as well, but found that it didn't work nearly as well as the toaster oven and since they cost about the same I highly recommend the oven over skillet...
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« Reply #9 on: April 18, 2014, 03:26:52 15:26 »

I looked on eBay this morning at the solder paste for sale. One look at it and I see why people aren't getting good results: FAKE SOLDER PASTE.

I've worked with all sorts of solder paste for the past 20 years and I can tell you, that isn't solder paste in the jar. That's fake or imitation solder paste. I deleted my smart-ass post directed at Parmin because he was probably using that "human excrement."

What is real solder paste? Isn't it just microscopic balls of solder with some thick flux mixed in? No, it's not. The non-solid (notice I did not say "liquid") component of the paste is a complex, precisely formulated gel compound with specific, unique physical properties that allows it to screen print well and then remain as non-slumping "bricks" sitting on the PCB pads.

See http://en.wikipedia.org/wiki/Solder_paste and http://en.wikipedia.org/wiki/Thixotropy

I don't know what is in that jar, but if those are real solder balls and not solder dust, I will guess that they've been salvaged from the end-of-run clean-up of production stenciling machines. Maybe the hardened, expired paste is dissolved in a solvent, cleaned and then some thick liquid flux added. The resulting slurry is then sold to unsuspecting suckers all over the world. (Hey, it must be real! It comes in a little plastic jar with a new label straight from China, right? And it's not like they would ever try to pass off fake, counterfeit, or adulterated goods. Nooo, not the Chinese, never.)

Article on Chinese solder paste: http://lowpowerlab.com/blog/2013/06/19/from-china-with-love-bad-solder-paste/


Chinese Solder Paste





Chinese Lion

« Last Edit: April 18, 2014, 03:44:17 15:44 by FriskyFerretReloaded2 » Logged
CocaCola
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« Reply #10 on: April 18, 2014, 04:43:46 16:43 »

As I said know your suppliers (using Ebay is not knowing your supplier) because as I also said there is a lot of counterfeit and garbage coming out of China...  The stuff I have received and used from China was always decent quality and worked well, can't say the same for any random Ebay purchase...

I have screened thousands upon thousands of boards at home using both name brand and Chinese solder paste, if the stuff I got from China didn't perform decently I would know...

So again know your suppliers and don't commit to any supplier until you have tested the product...
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« Reply #11 on: April 19, 2014, 02:01:32 02:01 »

The stuff I have received and used from China was always decent quality and worked well...

Would you mind sharing that supplier of quality solder paste with the forum? I for one would like a source of cheap but high quality solder paste.
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« Reply #12 on: April 19, 2014, 03:27:06 03:27 »

With all this garbage/fake paste on the market, who's got a recommendation for some good types?

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« Reply #13 on: April 19, 2014, 04:49:07 04:49 »

Would you mind sharing that supplier of quality solder paste with the forum? I for one would like a source of cheap but high quality solder paste.

Since it's been about 6 months since I last purchased and the supplier I used no longer list the exact stuff I had purchased I will not recommend said seller...  The small bottles it came in were bright yellow with the apparently ever popular 'BEST' brand label, not that that label or color of bottle means anything it's probably just the bottles they could get cheap at that moment in time...  It appears there is no shortage of different 'BEST' brand soldering paste and other items out there so I suspect at best they are just a repackager not an actual manufacture or they could be simply generic or bootleg labels being used by several companies, so who knows what you will actually get...

The small bottles are not that costly so it's not a huge lose if you get some bunk stuff, so next time I need some I'll probably just order a few different types and hope for the best or find a supplier that has customer feedback on the products...
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« Reply #14 on: April 21, 2014, 01:16:06 01:16 »

Is there any good alternative to solder paste Kester EP256?
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« Reply #15 on: April 21, 2014, 02:01:21 14:01 »

@CocaCola,

I just tried my first toaster oven reflow.

the PCB has 0603, and a difficult QFN with pads underneath also.

I bought a 25 toaster oven with fan ages ago, but never used it.

Today, I did the best i could laying the solder paste down ( multicore bought from Farnell, Sn/Pb 'cos its lower temperature).

I placed the components, set the toaster to 150C, then after a few minutes raised it to 200C, then after another 2 minute gave it the gun for 1 minute.

I watched the solder melt, add then turned the temperature dial back down to 150, to let it cool down.

then just turned the oven off after 5 minutes.

I have a Fluke Infra red temperature gun, so it was easy to just open the lid of the oven, and measure the temperatures.

I am most impressed, you gave me the kick to try this method.

Many thanks
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« Reply #16 on: April 21, 2014, 02:58:14 14:58 »

@CocaCola,
I bought a 25 toaster oven with fan ages ago, but never used it.

The internal circulation fan is the secret. The technical name for it is "forced convection." Makes all the difference as far as reflow.

So, to emphasize the points:

1. The reflow result was acceptable, or better.
2. You didn't need a PID temperature controller on the oven.
3. Running a strict time/temperature profile was unneeded for hobbyist or prototype work.
4. You didn't need to pay several hundred or several thousand dollars for an oven to get good results.
5. The robustness of modern all-purpose solder pastes is terrific.
6. The quality and freshness of the solder paste is all-important.

About your first reflow: Once reflow has finished you want to get the temperature down as quickly as possible but without causing thermal shock to the components. You can safely cool the board off much faster than you did. Once 100% of the pads have reflowed and coalesced into a mirror-like surface, you can turn the oven off and open the door wide open. Don't disturb the board until all the solder has become solid and then about another minute or two. After that time, remove the board to to a wire rack suspended a few inches above the work surface and allow to cool via natural convection. Do not lay the hot board flat on a cool surface. Do not use a fan to accelerate cooling.

Now try a plastic or metal solder paste stencil.

Let us see your work. Post a picture of the PCB. Use this image hoster unless you already have one. http://postimage.org/
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« Reply #17 on: April 21, 2014, 04:13:02 16:13 »

Excuse my noob question, but how do you even align a BGA at home ? Doesn't it need some expensive equipment to do it ?

I am quite used to soldering QFN && QFP with Flux alone. Check out this video for those interested, this is the easiest way I ever tried it takes seconds.

https://www.youtube.com/watch?v=6YU3v_w7x7o
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« Reply #18 on: April 21, 2014, 04:34:40 16:34 »

Excuse my noob question, but how do you even align a BGA at home ? Doesn't it need some expensive equipment to do it ?

If you have a decent silk screen you can use that if not do a dry fit and take use a marker to mark the board... The reflowing will 'pop' the chip into it's proper place as long as it's close, and if not in the middle of the reflow you can actually give the chip a slight tap or nudge with say some tweezers and it will self align while it's floating on the molten solder...  The previous assumes production quality boards with a good solder resist, can't say how well it will work on cheap boards with no resist or sloppy pads...

Quote
I am most impressed, you gave me the kick to try this method.

Glad it worked out...

Quote
I bought a 25 toaster oven with fan ages ago, but never used it.

A fan is a nice addition, my oven does not have one and because of that I don't get even heating especially towards to front of the oven, so when I place boards in the oven I have to remember to keep them all to the back and center or the front/side ones sometimes don't reflow properly, a fan should alleviate that issue...
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« Reply #19 on: April 21, 2014, 05:05:23 17:05 »

If you have a decent silk screen you can use that if not do a dry fit and take use a marker to mark the board... The reflowing will 'pop' the chip into it's proper place as long as it's close, and if not in the middle of the reflow you can actually give the chip a slight tap or nudge with say some tweezers and it will self align while it's floating on the molten solder...  The previous assumes production quality boards with a good solder resist, can't say how well it will work on cheap boards with no resist or sloppy pads...

Never thought that BGA soldering at home can be that "simple", I was looking online for some BGA rework stations and alignment equipment. I was always running away from BGA packages in my own projects, I will give this method a try. I am working on a design based on LPC1788, I will try the BGA package just for the fun of it.
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« Reply #20 on: April 21, 2014, 05:43:18 17:43 »

Never thought that BGA soldering at home can be that "simple"

Well I don't know if I would call it 'simple' as there is some skill involved, you are going to have to screen the solder paste on clean/crisp and then at least get the chip close without much shaking and moving as to not smear the paste around... A hand rest will help a lot...  If you don't have steady hands or good eyes it's going to really complicate things...  Like any SMD soldering there is a learning curve, but once you overcome that it becomes second nature...

Just for giggles Google up some Xbox RROD (red ring of death) repairs or xbox reflowing on youtube or whatever, there are tweens reflowing BGA chips in moms oven or with dads paint stripper heat gun Wink
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« Reply #21 on: April 21, 2014, 08:06:21 20:06 »

Well I don't know if I would call it 'simple' as there is some skill involved, you are going to have to screen the solder paste on clean/crisp and then at least get the chip close without much shaking and moving as to not smear the paste around... A hand rest will help a lot...  If you don't have steady hands or good eyes it's going to really complicate things...  Like any SMD soldering there is a learning curve, but once you overcome that it becomes second nature...

Just for giggles Google up some Xbox RROD (red ring of death) repairs or xbox reflowing on youtube or whatever, there are tweens reflowing BGA chips in moms oven or with dads paint stripper heat gun Wink

I am quite confident soldering QFN && QFP with a pitch down to 0.5mm with nothing but my soldering iron and some Chinese flux  Tongue , the latest being a Maxim Energy measurement chip with 64 pins. Not to count 0402,0603,0805,Melf and whatever there is. I put 'simple' in quotation on purpose, I know it will be a rough ride but it is something I never thought possible.

I heard a lot about the RROD, and made a little research about it. But again never occurred to me that some teens can do the repair in a hardcore DIY method. We learn something new everyday
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« Reply #22 on: April 21, 2014, 09:46:11 21:46 »

Any else notice the people asking the questions and getting the answers aren't using the "thank you" button?
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« Reply #23 on: April 22, 2014, 05:21:08 17:21 »

Another option for BGA prototyping...

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« Reply #24 on: April 22, 2014, 10:11:05 22:11 »

Another option for BGA prototyping...

And here is how it was made by someone with extreme patience.
Fine pitch BGA deadbug soldering: http://youtu.be/8DzTjzhVSIc
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