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SMT electronics assembly manufacturing forum.


To clean or not to Clean??

#11285

To clean or not to Clean?? | 29 May, 1999

I have always thought it to be a good practice to wash SMA's with water soluble paste (WS609) soon after reflow. Is there a time limit as to how long a board should sit after reflow before washing said board? For instance; processing a double-sided board that will sit in queue a few days before the other side is populated should you go ahead and wash the board? And if so, what about moisture entrapment from the wash machine. I have always washed the boards if they were going to sit overnight. But I am no expert, please help me O great ones

MDCox

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Jeff Sanchez

#11286

Re: To clean or not to Clean?? | 29 May, 1999

| | I have always thought it to be a good practice to wash SMA's with water soluble paste (WS609) soon after reflow. Is there a time limit as to how long a board should sit after reflow before washing said board? For instance; processing a double-sided board that will sit in queue a few days before the other side is populated should you go ahead and wash the board? And if so, what about moisture entrapment from the wash machine. I have always washed the boards if they were going to sit overnight. But I am no expert, please help me O great ones | | MDCox | | MD, I am no super exspert on all the many flux types myself. But I will share this. I ran some boards with water saluble flux and decided it was way to late to finish the job so I left them over night. What a mistake that was! All the solder joints turned black and oxidized. I had to reflow all the boards. I don't know exactly how long you have befor this occures. But I learned never to go past a half hour befor wash cycleing. I did a test by dropping some copper leads in a baby food jar to see how long it would take to do something and in three days the leads where compleatly gone! All that was left was a green copper oxide floating around in the bottom of the bottle.The flux was Kester 2331zx. I would never say water saluble flux is totaly bad. I think it is for me. I don't have all the right processes for it.But I did learn it demands a lot of care in your process handleing. If I where you I would wash them as soon as possible. Unless your shop is so proactive that you can assure that you can get back to that job within do time. Things happen, why risk it! It only takes a few minutes to wash and then your safe if something comes up. .............Jeff Sanchez

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Vic Lau

#11287

Re: To clean or not to Clean?? | 30 May, 1999

| | | | I have always thought it to be a good practice to wash SMA's with water soluble paste (WS609) soon after reflow. Is there a time limit as to how long a board should sit after reflow before washing said board? For instance; processing a double-sided board that will sit in queue a few days before the other side is populated should you go ahead and wash the board? And if so, what about moisture entrapment from the wash machine. I have always washed the boards if they were going to sit overnight. But I am no expert, please help me O great ones | | | | MDCox | | | | MD, I am no super exspert on all the many flux types myself. But I will share this. I ran some boards with water saluble flux and decided it was way to late to finish the job so I left them over night. What a mistake that was! All the solder joints turned black and oxidized. I had to reflow all the boards. I don't know exactly how long you have befor this occures. But I learned never to go past a half hour befor wash cycleing. I did a test by dropping some copper leads in a baby food jar to see how long it would take to do something and in three days the leads where compleatly gone! All that was left was a green copper oxide floating around in the bottom of the bottle.The flux was Kester 2331zx. I would never say water saluble flux is totaly bad. I think it is for me. I don't have all the right processes for it.But I did learn it demands a lot of care in your process handleing. If I where you I would wash them as soon as possible. Unless your shop is so proactive that you can assure that you can get back to that job within do time. Things happen, why risk it! It only takes a few minutes to wash and then your safe if something comes up. .............Jeff Sanchez | |

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Graham Naisbitt

#11288

Re: To clean or not to Clean?? | 30 May, 1999

| | | | | | I have always thought it to be a good practice to wash SMA's with water soluble paste (WS609) soon after reflow. Is there a time limit as to how long a board should sit after reflow before washing said board? For instance; processing a double-sided board that will sit in queue a few days before the other side is populated should you go ahead and wash the board? And if so, what about moisture entrapment from the wash machine. I have always washed the boards if they were going to sit overnight. But I am no expert, please help me O great ones | | | | | | MDCox | | | | | | MD, I am no super exspert on all the many flux types myself. But I will share this. I ran some boards with water saluble flux and decided it was way to late to finish the job so I left them over night. What a mistake that was! All the solder joints turned black and oxidized. I had to reflow all the boards. I don't know exactly how long you have befor this occures. But I learned never to go past a half hour befor wash cycleing. I did a test by dropping some copper leads in a baby food jar to see how long it would take to do something and in three days the leads where compleatly gone! All that was left was a green copper oxide floating around in the bottom of the bottle.The flux was Kester 2331zx. I would never say water saluble flux is totaly bad. I think it is for me. I don't have all the right processes for it.But I did learn it demands a lot of care in your process handleing. If I where you I would wash them as soon as possible. Unless your shop is so proactive that you can assure that you can get back to that job within do time. Things happen, why risk it! It only takes a few minutes to wash and then your safe if something comes up. .............Jeff Sanchez | | | | | | Hello folks,

The difference between a water soluble (OA) and a no-clean (NC) flux is that the OA is designed to be nicely aggressive at removing those nasty oxides and give you a nice soldered joint. A no-clean is intended to do the same job BUT, as there will always be residues, this must be a more benign material.

So, if you intend to run OA, WASH IT ASAP! That said, there are some OA materials that may permit washing to be done up to 2 weeks later but you really need to run trials to prove it - but if it simply means staying late on a Friday to wash the days production, the the boss will be a darn sight happier than if you return Monday to leadless components!

Regards, Graham

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JohnW

#11289

Re: To clean or not to Clean?? | 31 May, 1999

| | | | | | | | I have always thought it to be a good practice to wash SMA's with water soluble paste (WS609) soon after reflow. Is there a time limit as to how long a board should sit after reflow before washing said board? For instance; processing a double-sided board that will sit in queue a few days before the other side is populated should you go ahead and wash the board? And if so, what about moisture entrapment from the wash machine. I have always washed the boards if they were going to sit overnight. But I am no expert, please help me O great ones | | | | | | | | MDCox | | | | | | | | MD, I am no super exspert on all the many flux types myself. But I will share this. I ran some boards with water saluble flux and decided it was way to late to finish the job so I left them over night. What a mistake that was! All the solder joints turned black and oxidized. I had to reflow all the boards. I don't know exactly how long you have befor this occures. But I learned never to go past a half hour befor wash cycleing. I did a test by dropping some copper leads in a baby food jar to see how long it would take to do something and in three days the leads where compleatly gone! All that was left was a green copper oxide floating around in the bottom of the bottle.The flux was Kester 2331zx. I would never say water saluble flux is totaly bad. I think it is for me. I don't have all the right processes for it.But I did learn it demands a lot of care in your process handleing. If I where you I would wash them as soon as possible. Unless your shop is so proactive that you can assure that you can get back to that job within do time. Things happen, why risk it! It only takes a few minutes to wash and then your safe if something comes up. .............Jeff Sanchez | | | | | | | | | | | Hello folks, | | The difference between a water soluble (OA) and a no-clean (NC) flux is that the OA is designed to be nicely aggressive at removing those nasty oxides and give you a nice soldered joint. A no-clean is intended to do the same job BUT, as there will always be residues, this must be a more benign material. | | So, if you intend to run OA, WASH IT ASAP! That said, there are some OA materials that may permit washing to be done up to 2 weeks later but you really need to run trials to prove it - but if it simply means staying late on a Friday to wash the days production, the the boss will be a darn sight happier than if you return Monday to leadless components! | | Regards, Graham | | MD,

just cos I was bored and trying to avoid writing more of my thesis i thought I'd throw my tuppence worth in. Water wash paste is nasty stuff, that's why most places have jumped to the No Clean side. Assumming it's your box standard WS mix you definately dont want to waste any time in washing that stuff off. You may be lucky and find some of the board left there in the morning, but not much. Even if it's only mildly active it's gonna set in place and wait till the board is powered up so it can use the heat from the PCb to accelerate the process of eating the dam pcb. Washing the topside then building the bottom's shouldn't be too much of a worry, I'm taking it your using an in line wash which should dry the board and little dark corner's fairly well. As for the moisture ingress, it's likely to be fairly minimal at that stage i would guess. Depending on whether your gluing or pasting the bottom side you can get away without baking the boards with the glue since the temp's are a lot more device freindly and help in the baking altho not that much. Suppose the best advice is really build them both sides asap and throw them to the wash as they come off the line ( not forgetting to cool them a little first - thermal shock's a bitch!). but hey, why not just bite the bullet and move no clean for that brighter smile!!!!!

anyway's time I stoped rampling here and rampled on the thesis... now what was it on again..ha yes making Pizza's in a reflow oven that's right ( and yes it can be done!!!!!!! just rememebr to switch the N2 off or it dont rise)

outa here!!!

JohnW

reply »

JohnW

#11290

Re: To clean or not to Clean?? | 31 May, 1999

| | | | | | | | I have always thought it to be a good practice to wash SMA's with water soluble paste (WS609) soon after reflow. Is there a time limit as to how long a board should sit after reflow before washing said board? For instance; processing a double-sided board that will sit in queue a few days before the other side is populated should you go ahead and wash the board? And if so, what about moisture entrapment from the wash machine. I have always washed the boards if they were going to sit overnight. But I am no expert, please help me O great ones | | | | | | | | MDCox | | | | | | | | MD, I am no super exspert on all the many flux types myself. But I will share this. I ran some boards with water saluble flux and decided it was way to late to finish the job so I left them over night. What a mistake that was! All the solder joints turned black and oxidized. I had to reflow all the boards. I don't know exactly how long you have befor this occures. But I learned never to go past a half hour befor wash cycleing. I did a test by dropping some copper leads in a baby food jar to see how long it would take to do something and in three days the leads where compleatly gone! All that was left was a green copper oxide floating around in the bottom of the bottle.The flux was Kester 2331zx. I would never say water saluble flux is totaly bad. I think it is for me. I don't have all the right processes for it.But I did learn it demands a lot of care in your process handleing. If I where you I would wash them as soon as possible. Unless your shop is so proactive that you can assure that you can get back to that job within do time. Things happen, why risk it! It only takes a few minutes to wash and then your safe if something comes up. .............Jeff Sanchez | | | | | | | | | | | Hello folks, | | The difference between a water soluble (OA) and a no-clean (NC) flux is that the OA is designed to be nicely aggressive at removing those nasty oxides and give you a nice soldered joint. A no-clean is intended to do the same job BUT, as there will always be residues, this must be a more benign material. | | So, if you intend to run OA, WASH IT ASAP! That said, there are some OA materials that may permit washing to be done up to 2 weeks later but you really need to run trials to prove it - but if it simply means staying late on a Friday to wash the days production, the the boss will be a darn sight happier than if you return Monday to leadless components! | | Regards, Graham | | MD,

just cos I was bored and trying to avoid writing more of my thesis i thought I'd throw my tuppence worth in. Water wash paste is nasty stuff, that's why most places have jumped to the No Clean side. Assumming it's your box standard WS mix you definately dont want to waste any time in washing that stuff off. You may be lucky and find some of the board left there in the morning, but not much. Even if it's only mildly active it's gonna set in place and wait till the board is powered up so it can use the heat from the PCb to accelerate the process of eating the dam pcb. Washing the topside then building the bottom's shouldn't be too much of a worry, I'm taking it your using an in line wash which should dry the board and little dark corner's fairly well. As for the moisture ingress, it's likely to be fairly minimal at that stage i would guess. Depending on whether your gluing or pasting the bottom side you can get away without baking the boards with the glue since the temp's are a lot more device freindly and help in the baking altho not that much. Suppose the best advice is really build them both sides asap and throw them to the wash as they come off the line ( not forgetting to cool them a little first - thermal shock's a bitch!). but hey, why not just bite the bullet and move no clean for that brighter smile!!!!!

anyway's time I stoped rampling here and rampled on the thesis... now what was it on again..ha yes making Pizza's in a reflow oven that's right ( and yes it can be done!!!!!!! just rememebr to switch the N2 off or it dont rise)

outa here!!!

JohnW

reply »

#11291

Re: To clean or not to Clean?? | 31 May, 1999

| | I have always thought it to be a good practice to wash SMA's with water soluble paste (WS609) soon after reflow. Is there a time limit as to how long a board should sit after reflow before washing said board? For instance; processing a double-sided board that will sit in queue a few days before the other side is populated should you go ahead and wash the board? And if so, what about moisture entrapment from the wash machine. I have always washed the boards if they were going to sit overnight. But I am no expert, please help me O great ones | | MDCox | Hey Mike!!!

1 You're correct boards with OA flux should be water washed soon after reflow or wave soldering. How long after? Dunno. It depends on the activity of your flux, but if you wait too long just about any OA flux will start etching those bright shiney solder connections. We let boards sit no longer than 3 hours using WS750 paste. We use cheap cooking timers to keep track of the time. Check J-STD-001 for additional guidance. 2 Yes, you need to wash double-sided boards after soldering the first side, if you are not going to solder and wash the second side within your sit time. The same line of thought follows, if wave soldering is your next soldering step. 3 Yeabut, what about moisture entrapment from the wash machine? Never had a problem. Search the archives on this one. Intuitively, you're correct ... those boards should be wringing wet after that first side wash, but it just doesn't seem to be a problem. It might have something to do with:

1 In-bound board quality 2 Not a lot of board surface area that can absorb water 3 Who knows?

I just have always found something else to figure-out that seemed more pressing.

Good luck

Dave F

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