Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Selective Wave Solder Pallet

Ron H

#3239

Selective Wave Solder Pallet | 21 August, 2000

Problem: Flux remains on the board in the masked areas after the wave solder process.

We use Multicore X32-10m no clean flux. There is no post wave cleaning. While the flux residue is not conductive, it is unsightly and it may interfere with a bed-of nails type testing, although we currently do not test this way. How have others handled this problem?

I've thought about reducing the flux foam to a minimum height and decreasing the air flow to the air knife. Does anyone have any other suggestions? Thanks in advance.

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#3240

Re: Selective Wave Solder Pallet | 21 August, 2000

Question: Do you run your pallets hot or cold thru the wave?

I ask this because if you run your pallets cold the board will never preheat to the correct temp. thus, your flux won't activate properly.

James

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Ron H

#3241

Re: Selective Wave Solder Pallet | 21 August, 2000

The board and pallet are at room temperature when they pass thru the flux, then are sent thru a pre-heat section, and lastly sent over the wave solder. The exposed portions of the board solder properly.

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#3242

Re: Maybe a sprayfluxer will do | 22 August, 2000

Ron:It�s tricky to get what you want with this foamfluxers espacially using pallets. They got to be cleaned regularly. Most of the time excessive residues are removed using brushes which adds another process step. It should be better using a sprayfluxer especially one that�s capable of partial fluxing. Maybe some others out there have some experience with it and can make some comments.

Using foamfluxers with preheated pallets is IMO no good advice because the foam collapses with hot pallets. Using the air knife to remove excessive flux in combination with pallets also adds to the effect you encounter, the flux is forced under the pallet.

It will be tricky to adjust it to your satisfaction

Wolfgang

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#3243

Re: Maybe a sprayfluxer will do | 22 August, 2000

Actually Wolfgang that's what I was getting at. We use pallets all the time with a spray fluxer, hot pallets, and water soluble flux with minimum problems. My point was that if you use pallets at room temp the pallet sinks the heat and prevents the board from preheating properly which prevents the flux from activating properly. Does this make sense?

James

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#3244

Re: Maybe a sprayfluxer will do | 22 August, 2000

Hi James, the problem is, it�s not gonna work with foam fluxers. The problem with preheating didn�t occur to me, I got it to the desired limits using pallets. This might depend on the abilities of the used machine. If it�s working with your sprayfluxer it�s fine and saves you energy.

Wolfgang

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Ron H

#3245

Re: Maybe a sprayfluxer will do | 22 August, 2000

James, I'm a little curious about your wave solder process. Could you kindly discribe it and list the approximate associated temperatures? I think I'll fiddle with the spray flux idea. Thanks James and Wolfgang for your inputs. Ron

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#3246

Re: Maybe a sprayfluxer will do | 24 August, 2000

Me too. It was the first time that I heard about that "preheated pallet thing" and wonder to what temperature and with what kind of equipment it is heated up. Do different handling and transporttime have any effect on the resulting board temperature after preheating? Do operators wear gloves and do you need an extra operator at your line? Actually it doesn�t correspond with what I see at sites, adding another process step instead of placing the "through-holes" with the board already attached to the pallet and than put on the belt. Keep things as simple as possible, avoid process steps wherever possible, that�s just my opinion.

Wolfgang

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#3247

Re: Maybe a sprayfluxer will do | 24 August, 2000

Ok, here's why we preheat. In my limited experience at our facility I have found that preheating the pallets a half hour before running boards thru the wave helps create a better gasket. We were having problems where the first boards run with the pallets at room temp were getting solder worming its way between the board and pallet leaving solder residue on the boards that was hard to clean off. We only have a few pallets so when we run we just take them from the end and put them back thru the wave hot. So as you can see it is just the initial preheating that we do. We are an OEM and our DFM is non exsistant. I would love to glue bottomside parts and wave without a pallet but I can't get engineering to understand that parts need to be oriented a certain way and there are just some parts you can't put on the bottom and have them wave with any reliability.

Just the way it is.

James

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#3248

Re: Maybe a sprayfluxer will do | 24 August, 2000

I see that it�s not a well intended process you run, just born out of necessity. It�s good to see that someone always finds a solution (McGyver-like) if he encounters a problem although this one seems rather specific. Normally I would say "never change a winning team" but when it comes to process control and repeatability this seems quite uncontrollable. I know it�s hard to talk to management, CAD and engineers about DFM, I stick in the same mess and my fight is for nearly each "mil" and I have to rise my voice, demand 1000% and get maybe 50% ( always with the next project of cause ). Typical answers: - assembly is to stupid to get those things right - it takes to long layouttime which would cost much more money than anything else ( actually they have a pretty good understanding about their own costs ) - we only do a PCB and realize electrical performance and it�s not supposed to be build this way anyway ( but if it works it will be build over and over ) - ...

What helps is patience and persistence and meanwhile some tricks like yours.

Keep on fighting

Wolfgang

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