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Re: Black spots on gold finish pads.

Kallol Chakraborty

#13369

Re: Black spots on gold finish pads. | 30 November, 1998

Hi folks , Lately we are seeing a lot of rawcards with black spots on the pads - most of them have Au finish(immersion gold) . We did a lot of inspecton after wave solder and found that only (fine pitch) QFP are affected the most. Our inspection /testing process is to use the dental pick (90 deg. angle touching the lead to pad joint) on the leads. u-section reveals that the contamin looks like tar or oxide. Does anyone have any experience with this lately ?

Thanks in advence Kc.

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Earl Moon

#13370

Re: Black spots on gold finish pads. | 1 December, 1998

| Hi folks , | Lately we are seeing a lot of rawcards with black spots on the pads - most of them have Au finish(immersion gold) . We did a lot of inspecton after wave solder and found that only (fine pitch) QFP are affected the most. Our inspection /testing process is to use the dental pick (90 deg. angle touching the lead to pad joint) on the leads. | u-section reveals that the contamin looks like tar or oxide. | Does anyone have any experience with this lately ? | | Thanks in advence Kc. | It does get ugly, doesn't it? Where in the micro-section metallographic structure do you see the "spots?" Do they appear to extend all the way from the resin surface or the copper surface? What is your thickness specification for Au/Ni?

Likely it is not water staining you're seeing but too thin a layer of Nickel metallizsation (well under 100 millionths"). If this is the case, the Ni barrier is not capable of preventing the copper from "leaching" (copper plating thickness is about 1.2 additional mils on top of a foil thickness of about .7 of a mil) through to the gold and causing the appearance.

Copper, if not prevented by a sufficiently thick Ni barrier, will form an intermetallic with the gold and rapidly and excessively oxidize on the pad surface. Also, the Ni, when containing high phosphorous content (acceptable amounts not yet known) in the plating solution, will form an intermetallic with the Ni and oxidize possibly providing the evidence you see.

Now that you've x-sectioned, other metallographic analysis is advisable. Consult your independent test laboratory, or one you have internally, to find the best technique to determine exactly what the "tar" is really.

There are some big time experts capable of providing in depth analysis and advice on this subject. They reside at your board supplier's chemical suppliers. Often they participate in the IPC TechNet. Lately, as might be understood due to increased gold useage, there has been much concern and talk about immersion gold and attendant issues/problems. Much of this has been discussed and is archived.

Earl Moon

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kallol chakraborty

#13371

Re: Black spots on gold finish pads. | 1 December, 1998

| | Hi folks , | | Lately we are seeing a lot of rawcards with black spots on the pads - most of them have Au finish(immersion gold) . We did a lot of inspecton after wave solder and found that only (fine pitch) QFP are affected the most. Our inspection /testing process is to use the dental pick (90 deg. angle touching the lead to pad joint) on the leads. | | u-section reveals that the contamin looks like tar or oxide. | | Does anyone have any experience with this lately ? | | | | Thanks in advence Kc. | | | It does get ugly, doesn't it? Where in the micro-section metallographic structure do you see the "spots?" Do they appear to extend all the way from the resin surface or the copper surface? What is your thickness specification for Au/Ni? | | Likely it is not water staining you're seeing but too thin a layer of Nickel metallizsation (well under 100 millionths"). If this is the case, the Ni barrier is not capable of preventing the copper from "leaching" (copper plating thickness is about 1.2 additional mils on top of a foil thickness of about .7 of a mil) through to the gold and causing the appearance. | | Copper, if not prevented by a sufficiently thick Ni barrier, will form an intermetallic with the gold and rapidly and excessively oxidize on the pad surface. Also, the Ni, when containing high phosphorous content (acceptable amounts not yet known) in the plating solution, will form an intermetallic with the Ni and oxidize possibly providing the evidence you see. | | Now that you've x-sectioned, other metallographic analysis is advisable. Consult your independent test laboratory, or one you have internally, to find the best technique to determine exactly what the "tar" is really. | | There are some big time experts capable of providing in depth analysis and advice on this subject. They reside at your board supplier's chemical suppliers. Often they participate in the IPC TechNet. Lately, as might be understood due to increased gold useage, there has been much concern and talk about immersion gold and attendant issues/problems. Much of this has been discussed and is archived. | | Earl Moon | Thanks a bunch Earl, you are absolutely right. Ni plating is under spec. ......most of them are showing 20 ~ 45 uinches .... e-migration is a possibility.

Regards Kc.

reply »

Earl Moon

#13372

Re: Black spots on gold finish pads. | 1 December, 1998

| | | Hi folks , | | | Lately we are seeing a lot of rawcards with black spots on the pads - most of them have Au finish(immersion gold) . We did a lot of inspecton after wave solder and found that only (fine pitch) QFP are affected the most. Our inspection /testing process is to use the dental pick (90 deg. angle touching the lead to pad joint) on the leads. | | | u-section reveals that the contamin looks like tar or oxide. | | | Does anyone have any experience with this lately ? | | | | | | Thanks in advence Kc. | | | | | It does get ugly, doesn't it? Where in the micro-section metallographic structure do you see the "spots?" Do they appear to extend all the way from the resin surface or the copper surface? What is your thickness specification for Au/Ni? | | | | Likely it is not water staining you're seeing but too thin a layer of Nickel metallizsation (well under 100 millionths"). If this is the case, the Ni barrier is not capable of preventing the copper from "leaching" (copper plating thickness is about 1.2 additional mils on top of a foil thickness of about .7 of a mil) through to the gold and causing the appearance. | | | | Copper, if not prevented by a sufficiently thick Ni barrier, will form an intermetallic with the gold and rapidly and excessively oxidize on the pad surface. Also, the Ni, when containing high phosphorous content (acceptable amounts not yet known) in the plating solution, will form an intermetallic with the Ni and oxidize possibly providing the evidence you see. | | | | Now that you've x-sectioned, other metallographic analysis is advisable. Consult your independent test laboratory, or one you have internally, to find the best technique to determine exactly what the "tar" is really. | | | | There are some big time experts capable of providing in depth analysis and advice on this subject. They reside at your board supplier's chemical suppliers. Often they participate in the IPC TechNet. Lately, as might be understood due to increased gold useage, there has been much concern and talk about immersion gold and attendant issues/problems. Much of this has been discussed and is archived. | | | | Earl Moon | | | Thanks a bunch Earl, you are absolutely right. Ni plating is under spec. ......most of them are showing 20 ~ 45 uinches .... e-migration is a possibility. | | Regards Kc. | Kc,

Glad to help, but you would have figured this one out sooner than later. Could I ask a favor? Without comprimising confidentiallity, is it possible to receive a copy of the section in a jpeg format. I have a fairly good collection now, but in the interest of so many others experiencing this problem, and the fact I am writing an article on the subject - the more the better. If you cannot, I do understand.

Thanks,

Earl Moon

reply »

kallol Chakraborty

#13373

Re: Black spots on gold finish pads. | 4 December, 1998

| | | | Hi folks , | | | | Lately we are seeing a lot of rawcards with black spots on the pads - most of them have Au finish(immersion gold) . We did a lot of inspecton after wave solder and found that only (fine pitch) QFP are affected the most. Our inspection /testing process is to use the dental pick (90 deg. angle touching the lead to pad joint) on the leads. | | | | u-section reveals that the contamin looks like tar or oxide. | | | | Does anyone have any experience with this lately ? | | | | | | | | Thanks in advence Kc. | | | | | | | It does get ugly, doesn't it? Where in the micro-section metallographic structure do you see the "spots?" Do they appear to extend all the way from the resin surface or the copper surface? What is your thickness specification for Au/Ni? | | | | | | Likely it is not water staining you're seeing but too thin a layer of Nickel metallizsation (well under 100 millionths"). If this is the case, the Ni barrier is not capable of preventing the copper from "leaching" (copper plating thickness is about 1.2 additional mils on top of a foil thickness of about .7 of a mil) through to the gold and causing the appearance. | | | | | | Copper, if not prevented by a sufficiently thick Ni barrier, will form an intermetallic with the gold and rapidly and excessively oxidize on the pad surface. Also, the Ni, when containing high phosphorous content (acceptable amounts not yet known) in the plating solution, will form an intermetallic with the Ni and oxidize possibly providing the evidence you see. | | | | | | Now that you've x-sectioned, other metallographic analysis is advisable. Consult your independent test laboratory, or one you have internally, to find the best technique to determine exactly what the "tar" is really. | | | | | | There are some big time experts capable of providing in depth analysis and advice on this subject. They reside at your board supplier's chemical suppliers. Often they participate in the IPC TechNet. Lately, as might be understood due to increased gold useage, there has been much concern and talk about immersion gold and attendant issues/problems. Much of this has been discussed and is archived. | | | | | | Earl Moon | | | | | Thanks a bunch Earl, you are absolutely right. Ni plating is under spec. ......most of them are showing 20 ~ 45 uinches .... e-migration is a possibility. | | | | Regards Kc. | | | Kc, | | Glad to help, but you would have figured this one out sooner than later. Could I ask a favor? Without comprimising confidentiallity, is it possible to receive a copy of the section in a jpeg format. I have a fairly good collection now, but in the interest of so many others experiencing this problem, and the fact I am writing an article on the subject - the more the better. If you cannot, I do understand. | | Thanks, | | Earl Moon |

reply »

kallol chakraborty

#13374

Re: Black spots on gold finish pads. | 4 December, 1998

| | | | | Hi folks , | | | | | Lately we are seeing a lot of rawcards with black spots on the pads - most of them have Au finish(immersion gold) . We did a lot of inspecton after wave solder and found that only (fine pitch) QFP are affected the most. Our inspection /testing process is to use the dental pick (90 deg. angle touching the lead to pad joint) on the leads. | | | | | u-section reveals that the contamin looks like tar or oxide. | | | | | Does anyone have any experience with this lately ? | | | | | | | | | | Thanks in advence Kc. | | | | | | | | | It does get ugly, doesn't it? Where in the micro-section metallographic structure do you see the "spots?" Do they appear to extend all the way from the resin surface or the copper surface? What is your thickness specification for Au/Ni? | | | | | | | | Likely it is not water staining you're seeing but too thin a layer of Nickel metallizsation (well under 100 millionths"). If this is the case, the Ni barrier is not capable of preventing the copper from "leaching" (copper plating thickness is about 1.2 additional mils on top of a foil thickness of about .7 of a mil) through to the gold and causing the appearance. | | | | | | | | Copper, if not prevented by a sufficiently thick Ni barrier, will form an intermetallic with the gold and rapidly and excessively oxidize on the pad surface. Also, the Ni, when containing high phosphorous content (acceptable amounts not yet known) in the plating solution, will form an intermetallic with the Ni and oxidize possibly providing the evidence you see. | | | | | | | | Now that you've x-sectioned, other metallographic analysis is advisable. Consult your independent test laboratory, or one you have internally, to find the best technique to determine exactly what the "tar" is really. | | | | | | | | There are some big time experts capable of providing in depth analysis and advice on this subject. They reside at your board supplier's chemical suppliers. Often they participate in the IPC TechNet. Lately, as might be understood due to increased gold useage, there has been much concern and talk about immersion gold and attendant issues/problems. Much of this has been discussed and is archived. | | | | | | | | Earl Moon | | | | | | | Thanks a bunch Earl, you are absolutely right. Ni plating is under spec. ......most of them are showing 20 ~ 45 uinches .... e-migration is a possibility. | | | | | | Regards Kc. | | | | | Kc, | | | | Glad to help, but you would have figured this one out sooner than later. Could I ask a favor? Without comprimising confidentiallity, is it possible to receive a copy of the section in a jpeg format. I have a fairly good collection now, but in the interest of so many others experiencing this problem, and the fact I am writing an article on the subject - the more the better. If you cannot, I do understand. | | | | Thanks, | | | | Earl Moon | | | | Sorry Earl,

I am unable to find some pic for you - you are right all the pic has confidencial material on it - hope you understand. Thanks again for your help and good luck on your article - let me know where it is publishing so that I could take a look at it. I also have a bunch of info. on this kind of issues.

Regards Kc.

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