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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


EFData

#16228

Altera PQFP240 Solderability | 13 April, 1998

We are having some difficulty soldering a 240 pin Altera device. We use Alpha WS-609, a very generic profile for that solder paste, and a 6 mil stencil with laser cut apertures (1:1 ratio). This is a 20 mil pitch device (aperture size is 10 mils X 75 mils) and we are using HASL as the board finish. The manufacturer claims the lead frames are made from copper with an 85/15 tin lead finish. The results look suspiciously enough, like the results you might see if you were trying to solder to palladium (lifted leads sitting up on pillows, dull grainy joints). We suspect that because of our process time (25 minutes), the flux vehicle may be evaporating; we factory environment is consistently below 20% RH. Our experiments indicate that date code is not an issue and we have had parts tested for contaminants and only a slight black oxidation (whatever that means) was found Has anybody run into the same or similar problems? We are baffled.

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Justin Medernach

#16232

Re: Altera PQFP240 Solderability | 14 April, 1998

| We are having some difficulty soldering a 240 pin Altera device. We use Alpha WS-609, a very generic profile for that solder paste, and a 6 mil stencil with laser cut apertures (1:1 ratio). This is a 20 mil pitch device (aperture size is 10 mils X 75 mils) and we are using HASL as the board finish. | The manufacturer claims the lead frames are made from copper with an 85/15 tin lead finish. The results look suspiciously enough, like the results you might see if you were trying to solder to palladium (lifted leads sitting up on pillows, dull grainy joints). We suspect that because of our process time (25 minutes), the flux vehicle may be evaporating; we factory environment is consistently below 20% RH. Our experiments indicate that date code is not an issue and we have had parts tested for contaminants and only a slight black oxidation (whatever that means) was found | Has anybody run into the same or similar problems? We are baffled. Does that part still have a heat sink built into it or is it the plastic package? Justin

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Earl Moon

#16231

Re: Altera PQFP240 Solderability | 14 April, 1998

| We are having some difficulty soldering a 240 pin Altera device. We use Alpha WS-609, a very generic profile for that solder paste, and a 6 mil stencil with laser cut apertures (1:1 ratio). This is a 20 mil pitch device (aperture size is 10 mils X 75 mils) and we are using HASL as the board finish. | The manufacturer claims the lead frames are made from copper with an 85/15 tin lead finish. The results look suspiciously enough, like the results you might see if you were trying to solder to palladium (lifted leads sitting up on pillows, dull grainy joints). We suspect that because of our process time (25 minutes), the flux vehicle may be evaporating; we factory environment is consistently below 20% RH. Our experiments indicate that date code is not an issue and we have had parts tested for contaminants and only a slight black oxidation (whatever that means) was found | Has anybody run into the same or similar problems? We are baffled. It's the "slight" black oxidation that always gets my attention. If you have the oxide analyzed further, you may find excessive tin-oxide levels using SEM/EDX. This method provides a clear indication of what has been commonly found in industry when the tin immersion lead coating process is not effectively managed and/or handling and environmental issues are not addressed properly. You should perform solderability testing on these devices to see if wetting balance results indicate non-wetting. If either of the results mentioned are negative, the device leads will not wet as specified under any reflo solder conditions. Earl Moon

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EFData

#16233

Re: Altera PQFP240 Solderability | 14 April, 1998

| Does that part still have a heat sink built into it or is it the plastic package? | Justin Originally, we also thought the heat sink may be causing problems, so we conducted tests on both the plastic package and heat sink versions. Nothing conclusive arose out of either test.

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Lou

#16230

Re: Altera PQFP240 Solderability | 16 April, 1998

| We are having some difficulty soldering a 240 pin Altera device. We use Alpha WS-609, a very generic profile for that solder paste, and a 6 mil stencil with laser cut apertures (1:1 ratio). This is a 20 mil pitch device (aperture size is 10 mils X 75 mils) and we are using HASL as the board finish. | The manufacturer claims the lead frames are made from copper with an 85/15 tin lead finish. The results look suspiciously enough, like the results you might see if you were trying to solder to palladium (lifted leads sitting up on pillows, dull grainy joints). We suspect that because of our process time (25 minutes), the flux vehicle may be evaporating; we factory environment is consistently below 20% RH. Our experiments indicate that date code is not an issue and we have had parts tested for contaminants and only a slight black oxidation (whatever that means) was found | Has anybody run into the same or similar problems? We are baffled. Dear Earl, Poor solderability of HASL boards, is usually the result of poor wetting between the part to be solder and the solder. The presence of contaminants, tin oxides or copper-tin intermetallics could prevent good wetting. For instance, tin dioxide is a poor thermal and electrical conductor and it does not wet properly. In addition, there is plenty of evidence which shows that the presence of copper-tin intermetallic oxides makes soldering extremely diffult or impossible. The activity of the flux is important for removing the oxides and contaminants, however, when a thick oxide is present a very aggresive flux may be needed and sometimes that approach can not be used for copper-tin intermetallic oxides. Furthermore, a long process time(25 minutes) may promote the formation of thick oxides or if the HASL finish has not been applied uniformely over the PCB, it can promote the formation of copper-tin intermetallic oxides. SEM/EDX are good methods for detecting oxides, but it can't distinguish between oxidation stages wuithin a metal oxide. For instance, tin oxide (SnO) can be removed using an RMA type flux, but tin dioxide (SnO2) can't be fully removed using an RMA type flux. A more agressive flux or longer activation is needed when this oxide species is present. A more practical an useful method for testing oxides, contaminants and intermetallic oxides is the new SERA method. The SERA method will be presented in a seminar in Philadelphia on Friday, April 24 (during the Nepcon East week) and IPC has organized a SERA workshop during the IPC show in California. If you want more details about the SERA method and its applications to solderability, surface finish process control and evaluation of surface finish by detecting coating life and substrate protection contact me: Lou Madge at 973-773-8686 or e-mail LMadge@ecitechnology.com

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Lou

#16229

Re: Altera PQFP240 Solderability | 16 April, 1998

| We are having some difficulty soldering a 240 pin Altera device. We use Alpha WS-609, a very generic profile for that solder paste, and a 6 mil stencil with laser cut apertures (1:1 ratio). This is a 20 mil pitch device (aperture size is 10 mils X 75 mils) and we are using HASL as the board finish. | The manufacturer claims the lead frames are made from copper with an 85/15 tin lead finish. The results look suspiciously enough, like the results you might see if you were trying to solder to palladium (lifted leads sitting up on pillows, dull grainy joints). We suspect that because of our process time (25 minutes), the flux vehicle may be evaporating; we factory environment is consistently below 20% RH. Our experiments indicate that date code is not an issue and we have had parts tested for contaminants and only a slight black oxidation (whatever that means) was found | Has anybody run into the same or similar problems? We are baffled. Dear Earl, Poor solderability of HASL boards, is usually the result of poor wetting between the part to be solder and the solder. The presence of contaminants, tin oxides or copper-tin intermetallics could prevent good wetting. For instance, tin dioxide is a poor thermal and electrical conductor and it does not wet properly. In addition, there is plenty of evidence which shows that the presence of copper-tin intermetallic oxides makes soldering extremely diffult or impossible. The activity of the flux is important for removing the oxides and contaminants, however, when a thick oxide is present a very aggresive flux may be needed and sometimes that approach can not be used for copper-tin intermetallic oxides. Furthermore, a long process time(25 minutes) may promote the formation of thick oxides or if the HASL finish has not been applied uniformely over the PCB, it can promote the formation of copper-tin intermetallic oxides. SEM/EDX are good methods for detecting oxides, but it can't distinguish between oxidation stages wuithin a metal oxide. For instance, tin oxide (SnO) can be removed using an RMA type flux, but tin dioxide (SnO2) can't be fully removed using an RMA type flux. A more agressive flux or longer activation is needed when this oxide species is present. A more practical an useful method for testing oxides, contaminants and intermetallic oxides is the new SERA method. The SERA method will be presented in a seminar in Philadelphia on Friday, April 24 (during the Nepcon East week) and IPC has organized a SERA workshop during the IPC show in California. If you want more details about the SERA method and its applications to solderability, surface finish process control and evaluation of surface finish by detecting coating life and substrate protection contact me: Lou Madge at 973-773-8686 or e-mail LMadge@ecitechnology.com

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