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Water Soluble for No Clean BGA Balls

Dreamsniper

#28047

Water Soluble for No Clean BGA Balls | 13 April, 2004

Hi Guys,

Thanks for all your informative replies. I do know that Motorola is using a No Clean Eutectic Solder for their BGA's. We are in Aerospace and is using a Water Soluble Paste Flux.

Now,

a) Can anyone explain to me about the effect of their mixture.

b) What enhancement does my BGA will have when using a WS paste flux with regards to corrosion, 25 years life cycle of the solder joint.

c) What's the benefit in using a WS paste flux on a BGA with No Clean solder joint process?

d) Why can't I use a No Clean Flun only for that BGA which has a no clean process from the supplier?

e) Is the reason that I have to use a WS is that because it's Class 3 and is an Aerospace Standard.

f) Are all aerospace electronics products using Water Soluble for both flux and paste?

The reason is that I'm planning to apply a No Clean instead of Water Soluble just on the BGA pads for soldering to get rid of the flux residue issue that we can't remove from our BGA. And will just switch back to WS paste once we got the proper cleaning system.

Thanks and regards, Dreamy

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#28050

Water Soluble for No Clean BGA Balls | 13 April, 2004

Q1: Can anyone explain to me about the effect of their mixture. A1: What is their �mixture�?

Q2: What enhancement does my BGA will have when using a WS paste flux with regards to corrosion, 25 years life cycle of the solder joint. A2: Tough to say, which board has the lower level of harmful contaminants?

Q3: What's the benefit in using a WS paste flux on a BGA with No Clean solder joint process? A4: Assuming you solder NC / paste, reflow water washable BGA / wash, you get to turn all your NC solder connections a milky, white color, after washing. [And potentially freak every inspector down stream from washing.]

Q4: Why can't I use a No Clean Flux only for that BGA, which has a no clean process from the supplier? A4: Dunno, contract requirements?

Q5: Do I have to use a WS because it's Class 3 and is an Aerospace Standard? A5: It�s probably because your customer requires WS, not necessarily because it�s Class III or aerospace. There�s probably a NASA [er, somebody like that] requirement for water washable flux. [See with low stand-off devices, like some QFP and some BGA, washing OA improperly potentially is far more damaging than using NC. Which; if you plan to use a garden house, Dawn, and a scrub brush; to clean the board is what you will do.]

Q6: Are all aerospace electronics products using Water Soluble for both flux and paste? A6: No. Look here: http://www.bmpcoe.org/bestpractices/external/itt/itt_7.html

For better understanding flux classifications, look here: http://www.alphametals.com/products/fluxes/PDF/jstd004.pdf

S1: I do know that Motorola is using a No Clean Eutectic Solder for their BGA's. R1: Yes, but what market and customer requirements is Motorola using NC flux to solder their BGA?

S2: The reason is that I'm planning to apply a No Clean instead of Water Soluble just on the BGA pads for soldering to get rid of the flux residue issue that we can't remove from our BGA. And will just switch back to WS paste once we got the proper cleaning system. R2: Has your contract officer approved your plan to use multiple flux formulations on this board? This could be a very dangerous combination of materials.

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Dreamsniper

#28052

Water Soluble for No Clean BGA Balls | 13 April, 2004

Hi DaveF,

To explain. The BGA that we have is from Motorola. The solder balls of these BGA's are Eutectic Solder and processed using a NC flux (as per info from supplier). So this means that the BGA pad and solder connections had NC flux process. We are applying WS paste on our PCB's then place the BGA's from Motorola with a NC processes bonding between the ball and bga pad. Though we are getting good solder joint and drop on our BGA's after reflow soldering, I'm wondering what's the benefit of the WS paste flux under that BGA balls being processed by Motorola using an NC paste flux?

Just Imagine this:

My BGA pad to ball attachment is what, an NC paste flux processed or now a WS processed since during reflow the balls melt and did the WS paste flux cleaned the surface of my BGA pad prior to bonding? My PCB pad to BGA ball which has the WS paste flux applied is definitely cleaned by a WS OA flux.

Probably I'm a bit desperate with the issue of cleaning the flux from the BGA balls after reflow without proper cleaning system. It's like going to a war and fight without a gun and it's really disappointing.

If I could only talk to an ANT and teach him to go under those BGA's and clean them for...How's that?

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#28053

Water Soluble for No Clean BGA Balls | 13 April, 2004

Oy. So, what's your thinking on employing a contract cleaning specialist, until you have a proper cleaning system up and running?

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Dreamsniper

#28055

Water Soluble for No Clean BGA Balls | 13 April, 2004

Thanks. That's a good Idea. But question. Can a cleaning equipment (aqeous cleaner design for low standoff height parts) be able to clean my PCB given that the PCB sat in our production floor for 1 week prior to cleaning? Will the flux stick hard onto the joint and start degrading them? Is there a lead time or max time for the PCB to get cleaned?

thanks

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#28056

Water Soluble for No Clean BGA Balls | 13 April, 2004

Most 1.27 pitch BGA can be cleaned with modern machines. As far as the timing of cleaning OA flux res, obviously the sooner the better. After that different fluxes are different.

This must be a common question for cleaning professionals. They probably have innovative answers.

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#28057

Water Soluble for No Clean BGA Balls | 13 April, 2004

Hey Dreamy,

Dave is correct. If you attempt to clean your water soluble (OA) flux with water only, you will turn the no-clean flux white. No inspector or end-user will accept this.

If a proper cleaning system is not available to you, then I would recommend one of two things.

1. Utilize a contract cleaning service to properly clean your assemblies. We operate one (www.aqueoustech.com) and so does Austin America (www.aat-corp.com).

2. Buy cans of Micro-Care cleaning chemicals and manually pre-clean the no-clean flux thoroughly prior to using your dishwasher for OA flux. Soak the boards in solvent to ensure contact with the solvent and the area below the BGA. Once the boards are in your dishwasher, add some Cascade (or similar product) to lower the surface tension to assist in under-component penetration and the removal of cleaning chemical residue. Be sure to program a zillion rinses to ensure the dishwasher has removed all of the detergent form the rinse water. This is a labor intensive process but at least it will get you by until management decides its better to acquire a cleaning system rather than pay for the labor.

I am not familiar with any Aerospace specifications that mandate the use of OA flux. There are plenty of specifications that mandate specific post-reflow cleanliness levels. Basically, few agencies care what type of paste or flux you use rather, they case about the quality of the solder joint and the cleanliness levels.

Mike Konrad www.aqueousech.com konrad@aqueoustech.com

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#28058

Water Soluble for No Clean BGA Balls | 13 April, 2004

Dreamy,

OA fluxes / pastes have differing levels of activity. Most OA fluxes must be cleaned very soon after reflow. OA fluxes and pastes, while offering an aggressive flux package and a relatively easy removal (solubility in water), they are the worst if left on the board. Sometimes leaving OA flux on a board for one week is OK but most of the time the solder joint and component leads will be damaged.

No clean flux is no more difficult to remove after one week or one year than if cleaned immediately after reflow.

Best advice: Remove OA flux / paste immediately after reflow (at least within the same shift).

Mike Konrad www.aqueoustech.com konrad@aqueoustech.com

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#28059

Water Soluble for No Clean BGA Balls | 13 April, 2004

Hi Dreamsniper, It seen this is the major issue had been occurs you.( We had face all this issue last time too) We had done a lot of areospace products before and most of ours products is a must on class 3 spec. BGA is not that tough to clean of the flux whether is NC or WS. Is still depend on your process control and also the heigh of the BGA( after C4 ). It can also done by chemical wash if the products allow, and if this carry out you can use WS and NC at same board. Aerospace most of the requirement is ture perfer to use WS due to sometime there may had other process like underfill, encapsilation, EPIR... not only about the corr or clean issue. We had done may clean test, ion test, ftir.... Is still show WS is the best for class 3 products. Current our wash can perform to below 1.5mil washing and it had pass all test too. If you need more info please give me your email address.

Thanks. Workhard228

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Nick Prince

#28123

Water Soluble for No Clean BGA Balls | 18 April, 2004

"Thanks for all your informative replies. I do know that Motorola is using a No Clean Eutectic Solder for their BGA's. We are in Aerospace and is using a Water Soluble Paste Flux."

This statement is confusing me (not to difficult at my time of life). Motorola makes a device and attaches the balls with NC flux. They clean the device and pack it and ship it to you. You fit it using WS flux. Whats the problem? There is no No clean flux involved in the process, Motorola removed it. The package you get from them has no flux on it or in the balls. Or am I missing something?

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Ken

#28124

Water Soluble for No Clean BGA Balls | 18 April, 2004

Sounds reasonable. If there was NC flux "crud" on the balls, the vision processors of our P&P would have detection issues.

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