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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


joakim fagerlund

#14210

lid soldering problems (CQFP, Au/Sn solder) | 17 September, 1998

We have problems with voids when we solder lids to ceramic flatpackages. The sealring of the package is gold(100 micro inches or 2.5 micro meters)with a underlayer of Nickel The solder is attached to the lid (preform) and the solder material is Au/Sn (80/20 %) The package is heat treated twice before the soldering process. 1) Die adhesive (Silver-glass) hardening 1 hour and 45 min. Time above 350 deg.Celsius 15 min 2) Heat treatment in IR convection oven for 10 min. temp 370-420 deg. Celsius All heat treatments are done in Nitrogen atmoshere. The soldering process is done as recommended by the suppliers ( total time 30 min. and time over 280 deg. Celsius 4-5 min.) The flat packages and lids are stored in Nitrogen Does anybody know if there a risk of Nickel diffusion through the gold layer of the sealring ? Does Plasma washing/etching improve the soldering result ? Does anybody have any suggestions or recomendation I would be greatful !! Best regards Joakim Fagerlund

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Justin Medernach

#14212

Re: lid soldering problems (CQFP, Au/Sn solder) | 17 September, 1998

| We have problems with voids when we solder lids to | ceramic flatpackages. | The sealring of the package is gold(100 micro inches or 2.5 micro meters)with a underlayer of Nickel | The solder is attached to the lid (preform) and the solder material is Au/Sn (80/20 %) | The package is heat treated twice before the soldering | process. | 1) Die adhesive (Silver-glass) hardening | 1 hour and 45 min. | Time above 350 deg.Celsius 15 min | 2) Heat treatment in IR convection oven for | 10 min. temp 370-420 deg. Celsius | All heat treatments are done in Nitrogen atmoshere. | The soldering process is done as recommended by the suppliers ( total time 30 min. and time over 280 deg. Celsius 4-5 min.) | The flat packages and lids are stored in Nitrogen | Does anybody know if there a risk of Nickel diffusion | through the gold layer of the sealring ? | Does Plasma washing/etching improve the soldering result ? | Does anybody have any suggestions or recomendation | I would be greatful !! | Best regards Joakim Fagerlund Joakim, Thermocouple that component. It sounds to me like you have a problem with your profile for this application. You are using IR so the package is going to suck a lot of heat. You are also soldering with silver to gold. that requires an immense amount of heat in it's own right. find out what this assembly can take for a maximum temperature. It may be worth it to drill through a lid and insert a thermocouple. I suspect that the assembly isn't getting hot enough to form a good solder joint with all of the noble metal. Perhaps the plasma etch is a good idea but only etch the gold. Don't etch the lid. After etching, you're going to need to process immedeately as the oxidation window for exposed Ni is extremely short. just a few ideas. Regards, Justin Medernach

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Earl Moon

#14213

Re: lid soldering problems (CQFP, Au/Sn solder) | 18 September, 1998

| | We have problems with voids when we solder lids to | | ceramic flatpackages. | | The sealring of the package is gold(100 micro inches or 2.5 micro meters)with a underlayer of Nickel | | The solder is attached to the lid (preform) and the solder material is Au/Sn (80/20 %) | | The package is heat treated twice before the soldering | | process. | | 1) Die adhesive (Silver-glass) hardening | | 1 hour and 45 min. | | Time above 350 deg.Celsius 15 min | | 2) Heat treatment in IR convection oven for | | 10 min. temp 370-420 deg. Celsius | | All heat treatments are done in Nitrogen atmoshere. | | The soldering process is done as recommended by the suppliers ( total time 30 min. and time over 280 deg. Celsius 4-5 min.) | | The flat packages and lids are stored in Nitrogen | | Does anybody know if there a risk of Nickel diffusion | | through the gold layer of the sealring ? | | Does Plasma washing/etching improve the soldering result ? | | Does anybody have any suggestions or recomendation | | I would be greatful !! | | Best regards Joakim Fagerlund | Joakim, | Thermocouple that component. It sounds to me like you have a problem with your profile for this application. You are using IR so the package is going to suck a lot of heat. You are also soldering with silver to gold. that requires an immense amount of heat in it's own right. find out what this assembly can take for a maximum temperature. It may be worth it to drill through a lid and insert a thermocouple. I suspect that the assembly isn't getting hot enough to form a good solder joint with all of the noble metal. Perhaps the plasma etch is a good idea but only etch the gold. Don't etch the lid. After etching, you're going to need to process immedeately as the oxidation window for exposed Ni is extremely short. just a few ideas. | Regards, | Justin Medernach Justin, I agree with all you say except it is very risky, as you point to the short oxidation window for Ni (very high, immediate oxidation rate), to even attempt soldering at this level. Soldering to Ni is unacceptable. With micro inches gold over whatever amount Ni should see little diffusion of the type that would be deleterious to solder joint formation. When soldering any type ceramic, it almost becomes a brazing or welding process because of ceramic's insulative characteristics. As Justin says, get the facts and adjust temperatures accordingly. You will require much heat to do this job. Can you use other sealing techniques as epoxies or glass to metal seals or? Earl Moon

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Wayne Bracy

#14211

Re: lid soldering problems (CQFP, Au/Sn solder) | 22 September, 1998

| We have problems with voids when we solder lids to | ceramic flatpackages. | The sealring of the package is gold(100 micro inches or 2.5 micro meters)with a underlayer of Nickel | The solder is attached to the lid (preform) and the solder material is Au/Sn (80/20 %) | The package is heat treated twice before the soldering | process. | 1) Die adhesive (Silver-glass) hardening | 1 hour and 45 min. | Time above 350 deg.Celsius 15 min | 2) Heat treatment in IR convection oven for | 10 min. temp 370-420 deg. Celsius | All heat treatments are done in Nitrogen atmoshere. | The soldering process is done as recommended by the suppliers ( total time 30 min. and time over 280 deg. Celsius 4-5 min.) | The flat packages and lids are stored in Nitrogen | Does anybody know if there a risk of Nickel diffusion | through the gold layer of the sealring ? | Does Plasma washing/etching improve the soldering result ? | Does anybody have any suggestions or recomendation | I would be greatful !! | Best regards Joakim Fagerlund Joakim: Most hybrid packages that are hermetically sealed using solder reflow processes in a conveyor type reflow oven are sealed at above 283 degrees C (reflow temperature of the 80/20 preform)with the peak reflow zone in the area of 305 degrees to make sure that the entire preform and sealing rim reach the reflow temperature. Force used for clipping the lid to the package has also been a problem in the past. Not sure of the size of the ceramic package, but you might want to take a look at the procedure and make sure the pressure is adequate and the clip (s) placed properly for the size of the lid. A large number of ceramic packages are hermetically sealed using a process call parallel seamsealing. This process uses two electrodes with either AC or CD (capacitive discharge) current to provide the reflow temperature. Electric current is passed between the two electrodes with the heat concentrated on the lid and sealing rim surface. Internal temperartures to the critical devices is typically less than 100 degrees C. The parallel seamsealing unit is installed in an atmospheric enclosure glovebox) normally with a dewpoint level of around -65 degrees C. Prior to hermetically sealing the devices they are processed through a vacuum bakeout oven at a preseal bakeout temperature between 125 - 150 degrees and vacuum pressure of around 20 millitorr. The time for the bakeout will depend upon the size of the component, and permitted moisture content after sealing. Typically this amount will be less then 3000 ppm of gaseous particulate. Sealing yields are typically in the +99% range. New equipment is computer controlled,fully automatic and permits using pallets, Auer boat handling systems, lid feed and alignment systems with throughputs in the 1000 parts per hour range. Not as fast as a belt oven, but the yields are noramally higher and the look of the seal area is very good. Not sure if I got totally off the track, but just my two cents. Please email me if I can provide you with additional information. Regards,

Wayne

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