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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Ryan Jennens

#15723

Residue | 26 May, 1998

We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now.

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Chrys

#15731

Re: Residue | 26 May, 1998

| We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now. Ryan, I'd like to answer your questions, but first I have some of my own (so sorry): What type of flux - what's the solids content? What type of fluxer are you using? What type of preheaters are you using? How much solids are you putting on the board? What does the flux mfr recommend? Do you have a good way to measure? It sounds like you may be overactivating the flux and drying solids into the mask before the wave can squeegee them off, but I'm not sure without more info. Chrys

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Ryan Jennens

#15732

Re: Residue | 26 May, 1998

| | We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now. | Ryan, | I'd like to answer your questions, but first I have some of my own (so sorry): | What type of flux - what's the solids content? | What type of fluxer are you using? | What type of preheaters are you using? | How much solids are you putting on the board? What does the flux mfr recommend? Do you have a good way to measure? | It sounds like you may be overactivating the flux and drying solids into the mask before the wave can squeegee them off, but I'm not sure without more info. | Chrys

Thanks Chrys- We are using a low solids Alpha Lonco 26F. We will be trying Alpha RF800 low solids flux. We use a spray fluxer with two bottom side pre-heaters and one top side pre-heater (4 ft. long). We have no good way of measuring the solids content. How is this done?

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Graham Naisbitt

#15730

Re: Residue | 26 May, 1998

Ryan, Please consider the following: There is no such thing as no residue flux. Low or no solids flux contain "wetting" agents to help the stuff stick upside down! Try painting your ceiling with less than 2% solids paint!! With all this excess liquid, you need: A A higher preheat B Like anything that gets hot, the surface becomes more like a sponge, so you get absorbtion, often thru the resist, into the laminate. C You MAY have poor synergy between your flux and your resist. Any good news? Well.... You SHOULD try SIR testing your process to establish at which point the problem occurs. Test Coupon after each manufacturing stage. I can give you a load more if you give me your mailing address, please. Alternative? Alcohol based flux, which probably contain rosin, frequently react with certain types of cleaning agent - or - the alcohol based cleaning agent reacts with the no-clean residues to produce white powders. A major manufacturer has identified over 16 different types of white powder residue - so this is not as straightforward as you may think. I certainly recommend you talk to either Doug Pauls at CSL or Susan Mansilla at Robisan. They know about these issues. Get me a direct message, and I will send you their details. Good luck and regards, Graham Naisbitt | We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now.

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Chrys

#15733

Re: Residue | 27 May, 1998

| | | We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now. | | Ryan, | | I'd like to answer your questions, but first I have some of my own (so sorry): | | What type of flux - what's the solids content? | | What type of fluxer are you using? | | What type of preheaters are you using? | | How much solids are you putting on the board? What does the flux mfr recommend? Do you have a good way to measure? | | It sounds like you may be overactivating the flux and drying solids into the mask before the wave can squeegee them off, but I'm not sure without more info. | | Chrys | | Thanks Chrys- | We are using a low solids Alpha Lonco 26F. We will be trying Alpha RF800 | low solids flux. We use a spray fluxer with two bottom side pre-heaters and one top side | pre-heater (4 ft. long). We have no good way of measuring the solids content. How is this done? Hmm, Alpha Lonco 26F is pretty decent flux - it should behave well if the process window is correct. Graham has a point that you may be witnessing a chemical reaction between the mask or the fab house's cleaning chemistry, but I'd verify that the process is in the window before looking outside. Most of the flux "residues" should get squeegeed off by the smooth wave. It sounds like a silly question, but are you sure you're making good wave contact? Good solder joints are not necessarily an indicator of good contact. If only the leads and terminations are touching the solder wave, solder will wick up and make fine joints even though the substrate never touched the wave. You can verify good contact with a high temp glass plate. I get mine from a local glass shop - they cost about 20 bucks. It sounds like you have IR preheaters, which aren't prone for overdrying alcohol fluxes like convection ones are. I'd put a thermocouple or temperature sticker on the board to make sure it's getting to the right preheat. For measuring the amount of flux, get a piece of corrugated board and a scale accurate to .01 grams. Weigh the cardboard, flux it and weigh it again. Then calculate the deposition as: (Weight delta/area)* %solids by weight Convert it to micrograms/square inch and compare it to the manufacturer's recommendation. (You have to use cardboard with alcohol fluxes to slow their evaporation and get good data) I'll email you a copy of my Nepcon paper on characterizing fluxers. It explains it in more detail. Hope this helps. Chrys

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Earl Moon

#15725

Re: Residue | 27 May, 1998

| We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now. Back when, before DF and LPI solder masks, cure was a big issue. With DF type SM's it was difficult to determine cure. Then, as now, SM's are epoxy types and it is possible to determine cure using methelyne chloride (a drop at a time for one minute), in accordance with IPC-TM-650. If cured, the mask will show no degredation and will effectively resist nearly all other chemical assaults. A longer shot, but it might be helpful to make this determination if all else fails. Earl Moon

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Dave F

#15734

Re: Residue/Measuring Flux | 27 May, 1998

| | | | We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now. | | | Ryan, | | | I'd like to answer your questions, but first I have some of my own (so sorry): | | | What type of flux - what's the solids content? | | | What type of fluxer are you using? | | | What type of preheaters are you using? | | | How much solids are you putting on the board? What does the flux mfr recommend? Do you have a good way to measure? | | | It sounds like you may be overactivating the flux and drying solids into the mask before the wave can squeegee them off, but I'm not sure without more info. | | | Chrys | | | | Thanks Chrys- | | We are using a low solids Alpha Lonco 26F. We will be trying Alpha RF800 | | low solids flux. We use a spray fluxer with two bottom side pre-heaters and one top side | | pre-heater (4 ft. long). We have no good way of measuring the solids content. How is this done?

| Hmm, Alpha Lonco 26F is pretty decent flux - it should behave well if the process window is correct. Graham has a point that you may be witnessing a chemical reaction between the mask or the fab house's cleaning chemistry, but I'd verify that the process is in the window before looking outside. | Most of the flux "residues" should get squeegeed off by the smooth wave. It sounds like a silly question, but are you sure you're making good wave contact? Good solder joints are not necessarily an indicator of good contact. If only the leads and terminations are touching the solder wave, solder will wick up and make fine joints even though the substrate never touched the wave. You can verify good contact with a high temp glass plate. I get mine from a local glass shop - they cost about 20 bucks. | It sounds like you have IR preheaters, which aren't prone for overdrying alcohol fluxes like convection ones are. I'd put a thermocouple or temperature sticker on the board to make sure it's getting to the right preheat. | For measuring the amount of flux, get a piece of corrugated board and a scale accurate to .01 grams. Weigh the cardboard, flux it and weigh it again. Then calculate the deposition as: | (Weight delta/area)* %solids by weight | Convert it to micrograms/square inch and compare it to the manufacturer's recommendation. (You have to use cardboard with alcohol fluxes to slow their evaporation and get good data) | I'll email you a copy of my Nepcon paper on characterizing fluxers. It explains it in more detail. | Hope this helps. | Chrys Chyrs: Neat trick!!! If I know my flux density, how do I determine % solids by weight? Dave F

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Chrys

#15735

Re: Residue/Measuring Flux | 27 May, 1998

| | | | | We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now. | | | | Ryan, | | | | I'd like to answer your questions, but first I have some of my own (so sorry): | | | | What type of flux - what's the solids content? | | | | What type of fluxer are you using? | | | | What type of preheaters are you using? | | | | How much solids are you putting on the board? What does the flux mfr recommend? Do you have a good way to measure? | | | | It sounds like you may be overactivating the flux and drying solids into the mask before the wave can squeegee them off, but I'm not sure without more info. | | | | Chrys | | | | | | Thanks Chrys- | | | We are using a low solids Alpha Lonco 26F. We will be trying Alpha RF800 | | | low solids flux. We use a spray fluxer with two bottom side pre-heaters and one top side | | | pre-heater (4 ft. long). We have no good way of measuring the solids content. How is this done? | | | Hmm, Alpha Lonco 26F is pretty decent flux - it should behave well if the process window is correct. Graham has a point that you may be witnessing a chemical reaction between the mask or the fab house's cleaning chemistry, but I'd verify that the process is in the window before looking outside. | | Most of the flux "residues" should get squeegeed off by the smooth wave. It sounds like a silly question, but are you sure you're making good wave contact? Good solder joints are not necessarily an indicator of good contact. If only the leads and terminations are touching the solder wave, solder will wick up and make fine joints even though the substrate never touched the wave. You can verify good contact with a high temp glass plate. I get mine from a local glass shop - they cost about 20 bucks. | | It sounds like you have IR preheaters, which aren't prone for overdrying alcohol fluxes like convection ones are. I'd put a thermocouple or temperature sticker on the board to make sure it's getting to the right preheat. | | For measuring the amount of flux, get a piece of corrugated board and a scale accurate to .01 grams. Weigh the cardboard, flux it and weigh it again. Then calculate the deposition as: | | (Weight delta/area)* %solids by weight | | Convert it to micrograms/square inch and compare it to the manufacturer's recommendation. (You have to use cardboard with alcohol fluxes to slow their evaporation and get good data) | | I'll email you a copy of my Nepcon paper on characterizing fluxers. It explains it in more detail. | | Hope this helps. | | Chrys | Chyrs: Neat trick!!! If I know my flux density, how do I determine % solids by weight? Dave F Dave, If it's water based flux its easy. The specific gravity is so close to that of water, just multiply by the solids content. If it's alcohol based, you have to think back to chemistry class and do the math comparing the specific gravities. I did it a year or so ago and nearly gave myself an anurism. Then I gave it a little more thought, and decided to call the flux supplier and ask them. There's a bunch of chemists there who do that kind of math in their heads while they wait in line at the cafeteria. 1-800-2-KESTER. Ahh, no more brain strain. Work smarter, not harder. Chrys

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Chrys

#15724

Re: Residue | 27 May, 1998

| We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now. Guess what - I got those big, white, water droplet looking deposits of flux solids on my boards today! It reared its ugly head in final assembly. Hunted it down, and it turns out rework is much easier if the operator squirts a little wave soldering flux on the board instead of relying solely on the flux core in the solder. They usually wait for it to dry and brush the residue off, but we had a new operator who didn't know that neat little trick. Now obviously, if every board has spots, its not a rework issue. But, if some of the boards come out with spots, check their history and see if they've been through a rework loop. Happy Hunting, Chrys

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Dave F

#15726

Re: Residue/Cure Testing Of Solder Mask | 29 May, 1998

| | We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now. | Back when, before DF and LPI solder masks, cure was a big issue. With DF type SM's it was difficult to determine cure. Then, as now, SM's | are epoxy types and it is possible to determine | cure using methelyne chloride (a drop at a time | for one minute), in accordance with IPC-TM-650. If cured, the mask will show no degredation and | will effectively resist nearly all other chemical | assaults. | A longer shot, but it might be helpful to make | this determination if all else fails. | Earl Moon Earl: Must you run the methelyne chloride (a drop at a time for one minute), in accordance with IPC-TM-650 on an unprocessed board that you suspect is not cured properly? Or can you test a soldered board that you're sick about? ... In other words, does processing cure the uncured solder mask? Dave F

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Earl Moon

#15727

Re: Residue/Cure Testing Of Solder Mask | 29 May, 1998

| | | We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now. | | Back when, before DF and LPI solder masks, cure was a big issue. With DF type SM's it was difficult to determine cure. Then, as now, SM's | | are epoxy types and it is possible to determine | | cure using methelyne chloride (a drop at a time | | for one minute), in accordance with IPC-TM-650. If cured, the mask will show no degredation and | | will effectively resist nearly all other chemical | | assaults. | | A longer shot, but it might be helpful to make | | this determination if all else fails. | | Earl Moon | Earl: Must you run the methelyne chloride (a drop at a time for one minute), in accordance with IPC-TM-650 on an unprocessed board that you suspect is not cured properly? Or can you test a soldered board that you're sick about? ... In other words, does processing cure the uncured solder mask? Dave F

Dave, It would be a crap shoot. One of the reasons epoxy type solder masks are so desirable, over DF types, is that boards, for the most part are epoxy. Therefore, during the curing process, there occurs a degree of molecular x-linking between the mask and board surface - just as in the lamination and re-lamination process. Any additional attempts to achieve the desired effect would be unplanned and likely uncontrolled. Having said this, the mask may become "dry" but not achieve all specified requirements and still render undesirable effects as the problem discussed. Again, it's a supplier process control issue that must be addressed to prevent defect later. Sincerely, Earl Moon

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Dave F

#15728

Re: Residue/Cure Testing Of Solder Mask | 30 May, 1998

| | | | We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now. | | | Back when, before DF and LPI solder masks, cure was a big issue. With DF type SM's it was difficult to determine cure. Then, as now, SM's | | | are epoxy types and it is possible to determine | | | cure using methelyne chloride (a drop at a time | | | for one minute), in accordance with IPC-TM-650. If cured, the mask will show no degredation and | | | will effectively resist nearly all other chemical | | | assaults. | | | A longer shot, but it might be helpful to make | | | this determination if all else fails. | | | Earl Moon | | Earl: Must you run the methelyne chloride (a drop at a time for one minute), in accordance with IPC-TM-650 on an unprocessed board that you suspect is not cured properly? Or can you test a soldered board that you're sick about? ... In other words, does processing cure the uncured solder mask? Dave F | | Dave, | It would be a crap shoot. One of the reasons epoxy type solder masks are so desirable, over DF types, is that boards, for the most part are epoxy. Therefore, during the curing process, there occurs a degree of molecular x-linking between the mask and board surface - just as in the lamination and re-lamination process. | Any additional attempts to achieve the desired effect would be unplanned and likely uncontrolled. Having said this, the mask may become "dry" but not achieve all specified requirements and still render undesirable effects as the problem discussed. Again, it's a supplier process control issue that must be addressed to prevent defect later. | Sincerely, | Earl Moon Earl: So, would the IPC-TM-650 test show that that uncured mask was uncured on a board that has been processed? Dave F

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Earl Moon

#15729

Re: Residue/Cure Testing Of Solder Mask | 30 May, 1998

| | | | | We recently made the switch to no-clean and the wurface mount is turning out beautifully. However, the wave solder process continues to put up a fight; we are getting a white residue on the surface of the PCB. The residue is not localized to just the solder joints, but is similar to water spots on a car, it is on the PCB surface. We have played with the preheat temperatures and flux volume. But the flux volume cannot change too much as we are not getting very many solder problems (i.e. bridging, opens, etc.) Any ideas how to get rid of this residue. I realize some residue is expected, but the literature says the flux leaves none. Any ideas? We are using alcohol-based flux, for now. | | | | Back when, before DF and LPI solder masks, cure was a big issue. With DF type SM's it was difficult to determine cure. Then, as now, SM's | | | | are epoxy types and it is possible to determine | | | | cure using methelyne chloride (a drop at a time | | | | for one minute), in accordance with IPC-TM-650. If cured, the mask will show no degredation and | | | | will effectively resist nearly all other chemical | | | | assaults. | | | | A longer shot, but it might be helpful to make | | | | this determination if all else fails. | | | | Earl Moon | | | Earl: Must you run the methelyne chloride (a drop at a time for one minute), in accordance with IPC-TM-650 on an unprocessed board that you suspect is not cured properly? Or can you test a soldered board that you're sick about? ... In other words, does processing cure the uncured solder mask? Dave F | | | | Dave, | | It would be a crap shoot. One of the reasons epoxy type solder masks are so desirable, over DF types, is that boards, for the most part are epoxy. Therefore, during the curing process, there occurs a degree of molecular x-linking between the mask and board surface - just as in the lamination and re-lamination process. | | Any additional attempts to achieve the desired effect would be unplanned and likely uncontrolled. Having said this, the mask may become "dry" but not achieve all specified requirements and still render undesirable effects as the problem discussed. Again, it's a supplier process control issue that must be addressed to prevent defect later. | | Sincerely, | | Earl Moon | Earl: So, would the IPC-TM-650 test show that that uncured mask was uncured on a board that has been processed? Dave F yes

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