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Selective soldering pallets and solder balls

We're trying a selective soldering pallet for the first time... - Dec 02, 2002 by Steve Thomas  

#22556

Selective soldering pallets and solder balls | 2 December, 2002

We're trying a selective soldering pallet for the first time with mixed reviews. Are solder balls a prevalent problem with this process? Most of them seem to correspond with pallet wall locations....is it too much turbulence from the rotary chip wave? We've assumed that we'll need to use it to get good fill on the through-hole leads, but is it causing solder splashes and thus solder balls? Can preheat temps. affect the amount of solder coalescing in these locations? The pallet design has some pretty serious compromises because the target board was not designed with the process in mind, but the problem locations don't necessarily correspond with the compromises.

We do plan on running it without the chip wave to see what happens, but we're running with limited resources with respect to number of boards we can burn up and the number of people we can throw at process development, so I'm trying to keep the error side of "trial and error" to a minimum. Thanks.

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kenBliss

#22557

Selective soldering pallets and solder balls | 2 December, 2002

Hi Steve

The people who will have the answer is the experts at EMC Global Technologies. They know their stuff, they are the leader in the solder pallet industry. They design and build them to work right. http://www.emcgti.com for contact info. Hope that helps.

Ken Bliss

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RDR

#22560

Selective soldering pallets and solder balls | 2 December, 2002

If you can, attach athermocouple to the locations where you are getting solder balls. A previous product I had showed the same thing and we found that we had inadequate preheat leaving the liquid flux to splatter when it hit the wave. It could aslo be a non-contact of fixture to board surface. Are you using no-clean or Water soluble flux?

Hope this helps

Russ

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#22561

Selective soldering pallets and solder balls | 2 December, 2002

Unfortunately it's nc or we'd be worrying about this on the fly.

Non-contact is defintely and issue....this is an 18"x9" board with 1500 bottom side SMT parts that are scattered among the through-hole and vice-versa. We're currently using 7 hold-downs (just drilling the board out to match handy locations on the pallet) but it's still a crap shoot as to whether or not we have solder balling and where they'll be. We're going to try a little more flux and see what happens. The residues are light and almost all the balls are in board/pallet contact areas, typically not in open through-hole lead areas.

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Vince Whipple

#22564

Selective soldering pallets and solder balls | 2 December, 2002

Steve, I agree with the recommendation to check the temperature. This is the first place to go. Is this an IPA or water based Noclean? What is the topside temp of the assembly at the effected areas? If you are too cold you will have a tendency to have solder balls at the board pallet interface. If you are putting on too much flux, you will see most of the solder balls at the trailing edge interface. Again, TEMPERATURE is the important thing to know first off. Vince W

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Kris

#22566

Selective soldering pallets and solder balls | 2 December, 2002

Hi,

Try to check if there is water absorbed in the flux or the humidity around the wave area. possibly plating on barrels that might be damaged?

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#22576

Selective soldering pallets and solder balls | 3 December, 2002

We haven't run a profile yet....probably because we're a-feared to. We can't do topside preheating here to any degree because we use an aluminum plate for aligning hundreds of top side through-hole components (pots, switches, buttons, LEDs) that tend to melt when subjected to much heat conduction from the plate.

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Kris

#22579

Selective soldering pallets and solder balls | 3 December, 2002

This might be a trival mundane suggestion but try to use non conductive plate to hold components. Probably even made of the pallet material. I am sure your pallet fabricator will have tons of scrap and he can help you find one.

T

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#22583

Selective soldering pallets and solder balls | 3 December, 2002

At the price of Durapol we'd never get the OK to have them made. The Al fixtures are cheap and a quick turn local item.

As dense as the pth parts are I also don't think there'd be any room for any holes which I really think is the answer as far as heat transfer (regardless of the material)...not to mention needing to buy top side preheaters.

Thanks for your responses, though. As far as the cause of the splattering we don't have problems with normally processed boards, so I don't think it's a flux or board problem, but rather a matter of turbulence with the fixture. Not that I haven't been wrong on occasion, though.

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#22588

Selective soldering pallets and solder balls | 4 December, 2002

I have found that preheating the solder pallets prior to use helps cut down on the solder balling. Also, we do not cool the pallets between passes and we use a spray fluxer because a hot pallet will knock down the head on a foam fluxer. We use WS flux so I don't know if this will work with NC flux.

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Vince Whipple

#22590

Selective soldering pallets and solder balls | 4 December, 2002

By the way, what type of preheaters do you have? IR? Convection? If you have IR, there may be a way to cheat.

Vince W

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#22600

Selective soldering pallets and solder balls | 5 December, 2002

They're IR, bottom side only. Frankly wave solder is not my forte (there are those that would claim nothing is), but I've personally been tasked with developing a process to do reliable, high volume bottom side SMT, so I'm drawing a lot from the techs. on the practical stuff. Anyway I thought about a dwell over the preheat, but short of manually stopping the conveyor and starting it up again (not a very repeatable process), there's not way to do it. I'm not sure I'll get the desired affect anyway given that the board surface is not exposed to the IR preheaters where we're having the problems.

There's no such thing as cheating, only creative problem solving!

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William Guatemala

#22601

Selective soldering pallets and solder balls | 5 December, 2002

Have you check the flux gravity lately? If not, Check the flux gravity every 6 hours to make sure proper parameters are meet. Here is a list of things that may cause your solder ball problems; Excecive heat, defective fixtures, preheating temperatures are too high, moisture entrapped on your PCB's when it was fabricated, conveyor speed too fast, and or contaminated flux. Try to narrow this problems above, and you may have the solution. If the PCB's solder mask is improperly cured this causes blow holes splattering solder balls all over the areas.

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#22613

Selective soldering pallets and solder balls | 6 December, 2002

We only have solder balling problems in the interface of the pcb with the selective soldering pallet. All other boards (single, and double sided glue and waved alike) are fine, so I'm not thinking this is going to follow the normal path for resolution.

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Randy Villeneuve

#22642

Selective soldering pallets and solder balls | 10 December, 2002

Steve,

I wave solder most if not all our boards with selective wave pallets. I did not catch if the solder balls were on top of the board or on the bottom but that will make a difference on what to do to get rid of them. Pallets are good and bad. On the good side they hold the board flat and allow for component hold-downs etc. On the bad side they can trap flux between the pallet and the board which can in itself cause solder balling and can also leave a residue mark on the board. They also require allot more heat. IR lamps are pretty good for heating a pallet but you need to do a thermal profile to make sure your top side board temperature prior to the wave is around 110+-10 centigrade. I DO NOT recommend preheating a pallet or setting up a process that requires the pallet to be warm before sending in the machine. In most cases the pallet should be near room temperature prior to putting the pallet in the machine. If excess flux is apparent, use less flux. If your using a foam fluxer your going to have problems as there is little control and an air knife will do a good job of blowing flux under the pallet. If the solder balls are on the top of the board, reduce your wave height and turn off your chip wave. The chip wave will cause you problems with most pallets as it forces solder between the board and pallet. You can almost always get good hole fill with a lambda or "A" wave although I prefer a Lambda. Pallet design is critical and there are some really poor design house out there. When the board is in the pallet there should be no gaps visible between the board and the pallet. The area around the pockets (bottom side) should be relieved as much as possible to reduce and sharp transitions. I primarily use AGI out of Huntsville for my pallets and I have worked with ALL of the houses. I always do a first article on each pallet design and after making changes I then release the order for the remaining pallets. I also have a design guideline that they work to. Note: If you have a thermally conductive surface on the top of the parts you could be drawing too much heat from your components. Hope this helps.

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Jim Ferris

#22739

Selective soldering pallets and solder balls | 16 December, 2002

Randy, Steve & all,

Can you guys point me in the right direction when it come to using selective wave soldering...I am trying to get in-depth information on the Pro's & Con's of having our supplier use this process for our PWA's. (I can see there are some issues to deal with) We also need to understand what the industry trend is so that our designs will be portable from one manufacturer to the next.

I am told using IR Reflow for all SMT devices (both sides) is the way to go as opposed to using the wave to solder TH and discreet SMT on the bottom. I am told yields are better and that it could save us some $'s. Any thoughts? Is selective wave soldering considered "the wave" of the future?

Thanks Jim

PS. Steve, sorry I cannot be of any help with your issue!

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#22740

Selective soldering pallets and solder balls | 16 December, 2002

Jim

Consider issuing a purchase order to your assembler for the purchase of selective wave soldering pallets required to solder your board. That way, you: * Own the pallets. * Can take the pallets with you should you decide that another assembler can meet your requirements better than your current supplier.

As with everything you purchase, you should be involved with the important decisions in order to protect your interests. [This is not ment to be an insult, but just a running commentary.]

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#22744

Selective soldering pallets and solder balls | 16 December, 2002

Steve , I agree with all the responses you have received. Randy Villeneuve is absolutly correct in all of his assesments and I would consider him an expert with the process , Gris is correct about adding a "heat sink" to the process complicating pre-heat issues , and Vince Whipple is the expert on fluxing / fluxes.

Selective soldering is a much tighter process to control than open soldering of PTH components on a bare PCB. Many factors are involved in the successful implementation of the process , yet it is a very viable solution compared to other methods of soldering PTH components to a double sided , mixed technology PCA. Not every double sided , mixed technology PCA is a candidate for the process due to the spacing of the bottom side SMD devices from the PTH leads you wish to wett in the wave solder and the height of the bottom side SMD's being masked.

Solder balls are created by several factors , turbulence in the pallet apertures caused by PCA layout and pallet design, liquid flux not activated in pre-heat creating splatter , good flow height in the Lamina wave , etc.

The PCA being 9" x 18" indicates an issue of PCB warpage during wave solder processing. The pallet and the PCB in most cases want to move away from each other during pre-heat and the thermal dynamics of soldering , this is difficult to control because we are working against mother nature. There are several possible solutions yet it is difficult to comprehend the problems and potential solutions without more data on the PCA itself , each one presents a unique set of parameters.

I/we would be happy to assist in a potential solution discussion and implementation. Please reply with Gerber Data or JPEGS so our discussion can be more specific to your set of issues.

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Randy Villeneuve

#22752

Selective soldering pallets and solder balls | 17 December, 2002

Jim,

In most cases if you can eliminate a process you will save money. With that in mind, an all surface mount or all through hole design is prefered. There are alternatives to that rule, like hybrid designs that can be pin and paste soldered. It also depends to some point on where you want the product built as touch labor can be a big factor on cost. Note: Selective soldering has been around for some time but it does add cost to the product. For selective soldering you can can use a wave with a pallet or an alternate process like laser or softbeam soldering, etc.

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#22761

Selective soldering pallets and solder balls | 17 December, 2002

There are a few emerging technologies that have been growing in popularity for the past few years. Pin through paste, press fit connectors and selective soldering machines seem to be displacing custom fixtures. Most of the mixed technology boards only have connectors left on them as through hole components. Where do you see the market going? Being a fixture manufacturer I'd love to hear that fixtures are number one but how soon will new technology take to replace them? On the other hand, who has the money these days to buy a new piece of equipment to replace hard tooling? Whaddya' think?

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