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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Mark Quealy

#10536

Solder Paste from 500 gram tubes. | 20 July, 1999

I recently switched from solder paste in 500 gram jars to 500 gram tubes. I did this to try to limit the time the paste is exposed to the room environment. But we have a need to clean the stencil every 4 - 5 boards which means taking the bulk paste left on the screen and placing it into another container until the stencil is set up again. I am thinking of putting it into another tube to use on the next runs. What are others doing with paste between cleanings and when do they discard the paste?

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#10537

Re: Solder Paste from 500 gram tubes. | 20 July, 1999

| I recently switched from solder paste in 500 gram jars to 500 gram tubes. I did this to try to limit the time the paste is exposed to the room environment. But we have a need to clean the stencil every 4 - 5 boards which means taking the bulk paste left on the screen and placing it into another container until the stencil is set up again. I am thinking of putting it into another tube to use on the next runs. What are others doing with paste between cleanings and when do they discard the paste? | Mark: Resuing paste is not good practice, because the reused paste becomes:

1 Heavily oxidized 2 Dried out 3 Difficult to control

Common practice is to recycle used paste with wave solder dross.

As an alternative, consider that MPM and DEK (and maybe others) offer paste cartridges that do not require dumping a roll of paste on the stencil, but "wipe" paste from the cartridge to the stencil.

Appreciating that having said all that, you probably will need to continue to reuse paste. Take care not to contaminate the used paste with dried paste from previous recyling that is left on the empty tube.

Good luck

Dave F

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#10538

Re: Solder Paste from 500 gram tubes. | 20 July, 1999

| | I recently switched from solder paste in 500 gram jars to 500 gram tubes. I did this to try to limit the time the paste is exposed to the room environment. But we have a need to clean the stencil every 4 - 5 boards which means taking the bulk paste left on the screen and placing it into another container until the stencil is set up again. I am thinking of putting it into another tube to use on the next runs. What are others doing with paste between cleanings and when do they discard the paste? | | | Mark: Resuing paste is not good practice, because the reused paste becomes: | | 1 Heavily oxidized | 2 Dried out | 3 Difficult to control | | Common practice is to recycle used paste with wave solder dross. | | As an alternative, consider that MPM and DEK (and maybe others) offer paste cartridges that do not require dumping a roll of paste on the stencil, but "wipe" paste from the cartridge to the stencil. | | Appreciating that having said all that, you probably will need to continue to reuse paste. Take care not to contaminate the used paste with dried paste from previous recyling that is left on the empty tube. | | Good luck | | Dave F | Hi Mark, the amount of paste beeing actually printed compared to the amount of recycled or wasted paste tells you where your money goes. As long as I trust the printed paste on my boards to be good for soldering I trust the paste on the printer. While printing boards and boards you add more fresh paste without discarding the remainings from the printer. So just for cleaning purposes remove the paste, park in some clean container and use for the next printings. At the end of the day all the remainings normally should be removed and not be used anymore. I think that works with common pastes and under middle europian conditions but may be not in the tropics or subtropics where I have seen awful things but that�s another topic. Besides , I haven�t experienced any diffuculties with the 500gr. containers. They are just open to take paste out and then closed and sealed with tape immediatly.

Think about it Wolfgang

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DNC

#10539

Re: Solder Paste from 500 gram tubes. | 20 July, 1999

| I recently switched from solder paste in 500 gram jars to 500 gram tubes. I did this to try to limit the time the paste is exposed to the room environment. But we have a need to clean the stencil every 4 - 5 boards which means taking the bulk paste left on the screen and placing it into another container until the stencil is set up again. I am thinking of putting it into another tube to use on the next runs. What are others doing with paste between cleanings and when do they discard the paste? |

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DNC

#10540

Re: Solder Paste from 500 gram tubes. | 20 July, 1999

| I recently switched from solder paste in 500 gram jars to 500 gram tubes. I did this to try to limit the time the paste is exposed to the room environment. But we have a need to clean the stencil every 4 - 5 boards which means taking the bulk paste left on the screen and placing it into another container until the stencil is set up again. I am thinking of putting it into another tube to use on the next runs. What are others doing with paste between cleanings and when do they discard the paste? | Deon Response:

Hi Mark,

OOPS!! I screwed up on my first response. Hit the wrong button.

Well, I have been using solder paste in tubes for the last 4 years. I am very happy with the results that I am getting. Not being a very high volume manufacturer we only use enough paste to obtain about a 1/2" roll between squegees. This has cut down on our waste and extended the life of the remaining paste in the tube. We replenish the paste when the roll of paste gets dowm to about 1/4" in diameter. At the end of the shift we discard the paste and start off with a new batch very day. One thing to consider is that the cost of solder paste has gone down so much that it's really not worth risking the quality of the product for say $15.00 worth of paste.

What I would be concerned about is why are you having to clean your stencil after every 4 prints? I understand that if you are working with fine pitch it is good practice to wipe under stencil after every 3 or 4 prints, but to clean your entire stencil? If this is the case you have other very serious problems. Or if you mean to set up a different product after every 4 boards, then I would say replace the paste after about 6 hours of use. Hope this helps.

Regards,

Deon Nungaray SMT Mfg. Process Engineer GMI USA CA

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JohnW

#10541

Re: Solder Paste from 500 gram tubes. | 20 July, 1999

| | I recently switched from solder paste in 500 gram jars to 500 gram tubes. I did this to try to limit the time the paste is exposed to the room environment. But we have a need to clean the stencil every 4 - 5 boards which means taking the bulk paste left on the screen and placing it into another container until the stencil is set up again. I am thinking of putting it into another tube to use on the next runs. What are others doing with paste between cleanings and when do they discard the paste? | | | Deon Response: | | Hi Mark, | | OOPS!! I screwed up on my first response. Hit the wrong button. | | Well, I have been using solder paste in tubes for the last 4 years. I am very happy with the results that I am getting. | Not being a very high volume manufacturer we only use enough paste to obtain about a 1/2" roll between squegees. This has cut down on our waste and extended the life of the remaining paste in the tube. We replenish the paste when the roll of paste gets dowm to about 1/4" in diameter. At the end of the shift we discard the paste and start off with a new batch very day. One thing to consider is that the cost of solder paste has gone down so much that it's really not worth risking the quality of the product for say $15.00 worth of paste. | | What I would be concerned about is why are you having to clean your stencil after every 4 prints? I understand that if you are working with fine pitch it is good practice to wipe under stencil after every 3 or 4 prints, but to clean your entire stencil? If this is the case you have other very serious problems. Or if you mean to set up a different product after every 4 boards, then I would say replace the paste after about 6 hours of use. Hope this helps. | | Regards, | | Deon Nungaray | SMT Mfg. Process Engineer | GMI USA CA | Mark,

Deon has some good point's, but I have the same question..why are you cleaning the stencil ever 4 boards ? The thought's I have are that amybe you could cut down the paste your using on the stencil then there isn't that much to worry about you can get away with as little as 0.5-1inch of paste and just replenish it a little more often. In term's of putting it into tub's, we do that were i am and i have to say I'm not a big fan of it. My feeling is that depending on how long it's in the tub the oxidisation that's taking place can only be a bad thing. I've seen it when the paste has dried out a little folk's mixing in some new stuff in the belief that this will make it ok....I tend to argue this. To mix it in a tub people sturr and fold the paste together or even do it without mixing paste I think it's an inbuilt desire to sturn and mix stuff in tub's. Anyway's the other thing that you would mix in this way is bread..so you can trap air to make it rise...not what you want in your solder paste! We are putting a lot of focus on better control of paste and only using the right amount's which help's in your problem anout reuse. But your other problem is the cleaning...why are you having to do it so often and what type of printer are you using ? DEk's and MPM's have their own in built cleaner's that can be used or if it's a slightly older version you can still clean it by hand without removing all the paste by using silk wipes or something similar.

don't know if my ramblings are any help Mark but some more info on why your cleaning so often and why you decant the paste would be interesting.

JohnW

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ScottM

#10542

Re: Solder Paste from 500 gram tubes. | 21 July, 1999

| I recently switched from solder paste in 500 gram jars to 500 gram tubes. I did this to try to limit the time the paste is exposed to the room environment. But we have a need to clean the stencil every 4 - 5 boards which means taking the bulk paste left on the screen and placing it into another container until the stencil is set up again. I am thinking of putting it into another tube to use on the next runs. What are others doing with paste between cleanings and when do they discard the paste? | I tried it a year ago but wasn't pleased with the results, it wasn't a drop in process. Because of the nature of dispensing, my rep. said they changed the chemistry a "bit" and that it tends to "settle" over time (don't buy too much at a time!) and you may want to "spin" the cartriges in storage. My operators complained about the consistancy and print characteristics. Wasn't worth the effort.

With proper solder paste management, get it out, and put the lids back on (always use both, the first to squeeze out the air, the second to seal it) works quite well. With this I've been able to use the unused solder paste the next day on jelly bean boards. But NEVER reuse paste that's spent time on the stencil.

Then there's Oasis... they redefined these rules!

Hope this helps, Scott

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Mark Quealy

#10543

Re: Solder Paste from 500 gram tubes. | 21 July, 1999

| | | I recently switched from solder paste in 500 gram jars to 500 gram tubes. I did this to try to limit the time the paste is exposed to the room environment. But we have a need to clean the stencil every 4 - 5 boards which means taking the bulk paste left on the screen and placing it into another container until the stencil is set up again. I am thinking of putting it into another tube to use on the next runs. What are others doing with paste between cleanings and when do they discard the paste? | | | | | Deon Response: | | | | Hi Mark, | | | | OOPS!! I screwed up on my first response. Hit the wrong button. | | | | Well, I have been using solder paste in tubes for the last 4 years. I am very happy with the results that I am getting. | | Not being a very high volume manufacturer we only use enough paste to obtain about a 1/2" roll between squegees. This has cut down on our waste and extended the life of the remaining paste in the tube. We replenish the paste when the roll of paste gets dowm to about 1/4" in diameter. At the end of the shift we discard the paste and start off with a new batch very day. One thing to consider is that the cost of solder paste has gone down so much that it's really not worth risking the quality of the product for say $15.00 worth of paste. | | | | What I would be concerned about is why are you having to clean your stencil after every 4 prints? I understand that if you are working with fine pitch it is good practice to wipe under stencil after every 3 or 4 prints, but to clean your entire stencil? If this is the case you have other very serious problems. Or if you mean to set up a different product after every 4 boards, then I would say replace the paste after about 6 hours of use. Hope this helps. | | | | Regards, | | | | Deon Nungaray | | SMT Mfg. Process Engineer | | GMI USA CA | | | Mark, | | Deon has some good point's, but I have the same question..why are you cleaning the stencil ever 4 boards ? | The thought's I have are that amybe you could cut down the paste your using on the stencil then there isn't that much to worry about you can get away with as little as 0.5-1inch of paste and just replenish it a little more often. In term's of putting it into tub's, we do that were i am and i have to say I'm not a big fan of it. | My feeling is that depending on how long it's in the tub the oxidisation that's taking place can only be a bad thing. I've seen it when the paste has dried out a little folk's mixing in some new stuff in the belief that this will make it ok....I tend to argue this. To mix it in a tub people sturr and fold the paste together or even do it without mixing paste I think it's an inbuilt desire to sturn and mix stuff in tub's. Anyway's the other thing that you would mix in this way is bread..so you can trap air to make it rise...not what you want in your solder paste! | We are putting a lot of focus on better control of paste and only using the right amount's which help's in your problem anout reuse. | But your other problem is the cleaning...why are you having to do it so often and what type of printer are you using ? DEk's and MPM's have their own in built cleaner's that can be used or if it's a slightly older version you can still clean it by hand without removing all the paste by using silk wipes or something similar. | | don't know if my ramblings are any help Mark but some more info on why your cleaning so often and why you decant the paste would be interesting. | | JohnW

OK, I'm using a Transition Automation, Semi-automatic printer with frameless laser cut 6 mil stencils. We have a single QUAD IVc for placement. Depending how long the board is on the machine is the cycle for printing. This is mainly due to room environment conditions which has AC but is not tightly controled. Humidity not at all. So typically we don't batch print. If a board takes 6 minutes on the QUAD we print every 6 minutes. By the 5 board the fine pitch (.40mm) apertures (1:1) are clogged.

Mark |

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DNC

#10544

Re: Solder Paste from 500 gram tubes. | 21 July, 1999

| | | | I recently switched from solder paste in 500 gram jars to 500 gram tubes. I did this to try to limit the time the paste is exposed to the room environment. But we have a need to clean the stencil every 4 - 5 boards which means taking the bulk paste left on the screen and placing it into another container until the stencil is set up again. I am thinking of putting it into another tube to use on the next runs. What are others doing with paste between cleanings and when do they discard the paste? | | | | | | | Deon Response: | | | | | | Hi Mark, | | | | | | OOPS!! I screwed up on my first response. Hit the wrong button. | | | | | | Well, I have been using solder paste in tubes for the last 4 years. I am very happy with the results that I am getting. | | | Not being a very high volume manufacturer we only use enough paste to obtain about a 1/2" roll between squegees. This has cut down on our waste and extended the life of the remaining paste in the tube. We replenish the paste when the roll of paste gets dowm to about 1/4" in diameter. At the end of the shift we discard the paste and start off with a new batch very day. One thing to consider is that the cost of solder paste has gone down so much that it's really not worth risking the quality of the product for say $15.00 worth of paste. | | | | | | What I would be concerned about is why are you having to clean your stencil after every 4 prints? I understand that if you are working with fine pitch it is good practice to wipe under stencil after every 3 or 4 prints, but to clean your entire stencil? If this is the case you have other very serious problems. Or if you mean to set up a different product after every 4 boards, then I would say replace the paste after about 6 hours of use. Hope this helps. | | | | | | Regards, | | | | | | Deon Nungaray | | | SMT Mfg. Process Engineer | | | GMI USA CA | | | | | Mark, | | | | Deon has some good point's, but I have the same question..why are you cleaning the stencil ever 4 boards ? | | The thought's I have are that amybe you could cut down the paste your using on the stencil then there isn't that much to worry about you can get away with as little as 0.5-1inch of paste and just replenish it a little more often. In term's of putting it into tub's, we do that were i am and i have to say I'm not a big fan of it. | | My feeling is that depending on how long it's in the tub the oxidisation that's taking place can only be a bad thing. I've seen it when the paste has dried out a little folk's mixing in some new stuff in the belief that this will make it ok....I tend to argue this. To mix it in a tub people sturr and fold the paste together or even do it without mixing paste I think it's an inbuilt desire to sturn and mix stuff in tub's. Anyway's the other thing that you would mix in this way is bread..so you can trap air to make it rise...not what you want in your solder paste! | | We are putting a lot of focus on better control of paste and only using the right amount's which help's in your problem anout reuse. | | But your other problem is the cleaning...why are you having to do it so often and what type of printer are you using ? DEk's and MPM's have their own in built cleaner's that can be used or if it's a slightly older version you can still clean it by hand without removing all the paste by using silk wipes or something similar. | | | | don't know if my ramblings are any help Mark but some more info on why your cleaning so often and why you decant the paste would be interesting. | | | | JohnW | | OK, I'm using a Transition Automation, Semi-automatic printer with frameless laser cut 6 mil stencils. We have a single QUAD IVc for placement. Depending how long the board is on the machine is the cycle for printing. This is mainly due to room environment conditions which has AC but is not tightly controled. Humidity not at all. So typically we don't batch print. If a board takes 6 minutes on the QUAD we print every 6 minutes. By the 5 board the fine pitch (.40mm) apertures (1:1) are clogged. | | Mark | | | Deon Response:

Hi Mark,

From what you are saying I would check my printing parameters. We have done a process similar to what you are doing. The way we kept the apertures from clogging was by using the snap off printing method. I know a lot of people do not like to use snap off, but it works just fine for us. Repeatable, consistent and accurate. Another thing to consider is using a framed stencil instead of frameless. This will improve your paste release. Thus better paste release means no clogged apertures. Try it. Good Luck.

Deon Nungaray SMT Mfg. Process Engineer GMI USA CA |

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