Gold boards OK with SMT?

Is there any problem using SMT on gold boards? 15 years ago we were told not to use gold boards, but I can't remember why. Judging by the other postings it now appears to be common. Only problem I see is that the nickel should be plated, not electroless. My vendor wants to switch to gold to get around some problems with the key contacts that currently use carbon. Hope this isn't too elementary. I am a design guy, not a process guy. Thanks, Paul

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| Is there any problem using SMT on gold boards? 15 years ago we were told not to use gold boards, but I can't remember why. Judging by the other postings it now appears to be common. Only problem I see is that the nickel should be plated, not electroless. My vendor wants to switch to gold to get around some problems with the key contacts that currently use carbon. | Hope this isn't too elementary. I am a design guy, not a process guy. | Thanks, | Paul Paul- In our process we use both carbon and Gold fingers for our switches, The biggest saving you'll see between the two is, no more carbon voids or bridging. The gold will also carry a longer cycle life than the carbon. As far as the component pads are concerned, we run one board that is all gold plated, and the only manufacturing issue that we've run into is the added cost...copper or nickel is cheaper. -Ben

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| | Is there any problem using SMT on gold boards? 15 years ago we were told not to use gold boards, but I can't remember why. Judging by the other postings it now appears to be common. Only problem I see is that the nickel should be plated, not electroless. My vendor wants to switch to gold to get around some problems with the key contacts that currently use carbon. | | Hope this isn't too elementary. I am a design guy, not a process guy. | | Thanks, | | Paul | Paul- | In our process we use both carbon and Gold fingers for our switches, The biggest saving you'll see between the two is, no more carbon voids or bridging. | The gold will also carry a longer cycle life than the carbon. As far as the component pads are concerned, we run one board that is all gold plated, and the only manufacturing issue that we've run into is the added cost...copper or nickel is cheaper. | -Ben As you are aware there are a lot of pros and cons for gold boards they should not be more expensive that HASL. The price will depend on the way the fabrication is costed. The carbon work fine and as Ben said are cheaper. A review of different solder finishes and the costs are on a download document on my web page under process documents.

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| Is there any problem using SMT on gold boards? 15 years ago we were told not to use gold boards, but I can't remember why. Judging by the other postings it now appears to be common. Only problem I see is that the nickel should be plated, not electroless. My vendor wants to switch to gold to get around some problems with the key contacts that currently use carbon. | Hope this isn't too elementary. I am a design guy, not a process guy. | Thanks, | Paul There may be good reasons not to use gold boards as is being discussed all over the planet, especially the IPC TechNet. It used to be gold was electroplated in copious amounts (when gold was cheap - up to 50 millionths, etc.). Gold was then "leached" off board surfaces before through hole/wave soldering to ensure embrittlement did not reduce initial solder joint quality and long term reliability. Recently, in the past few years, "newer" electroless processes provide minute amounts of gold (deposited through electroless processing) over electroless nickel. All was thought to be well but the culprit in the equation is the phosphorous intermetallic formations providing a failure mechanism as an effect of the electroless nickel deposition process. The gold is no longer a problem as it does not exceed solder contamination/purity requirements stated in ANSI/J-STD-001, figure 5-1, on page 5. The problem is the phosphorous used both in electroless and electroplating baths. Ask Motorols and othe industry "giants". Also, ask industry what can be done to prevent the problem. We all need a way out of HASL. Earl Moon

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| | Is there any problem using SMT on gold boards? 15 years ago we were told not to use gold boards, but I can't remember why. Judging by the other postings it now appears to be common. Only problem I see is that the nickel should be plated, not electroless. My vendor wants to switch to gold to get around some problems with the key contacts that currently use carbon. | | Hope this isn't too elementary. I am a design guy, not a process guy. | | Thanks, | | Paul | Paul- | In our process we use both carbon and Gold fingers for our switches, The biggest saving you'll see between the two is, no more carbon voids or bridging. | The gold will also carry a longer cycle life than the carbon. As far as the component pads are concerned, we run one board that is all gold plated, and the only manufacturing issue that we've run into is the added cost...copper or nickel is cheaper. | -Ben

Folks, I want to reiterate my chief concern about electroless gold over electroless nickel. I have advocated the process since its inception. I posted this objective view in the June (now archived very kindly) forum. The following reply, and personal email, was received at that time: There has been a problem with nickel/gold plating both on PCB's as well as BGA package substrates. The problem only occurs with electroless nickel/gold plating. In electroless nickel plating, phosphorus is added to the plating baths. When you solder to the nickel/gold pad, the phosphorus migrates to the surface of the nickel, forming a very brittle phosphorus/tin intermetallic between the nickel and your tin/lead solder. If you use electrolytic plating you should not have a problem, since phosphorus is not necessary to plate for nickel with this plating method. Many of the early BGA's used electroless nickel/gold plating on the substrates solder pads. Those suppliers who are aware of the problem have switched to electrolytic plating. You should check with your BGA component supplier as well as your PCB supplier. If you have any questions you can call me at 512-933-5783. This is more than cause for concern. Therefore, I urge us all to look more closely and deeply into this subject and the processes required to effect acceptable solder joints. Earl Moon

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| Is there any problem using SMT on gold boards? 15 years ago we were told not to use gold boards, but I can't remember why. Judging by the other postings it now appears to be common. Only problem I see is that the nickel should be plated, not electroless. My vendor wants to switch to gold to get around some problems with the key contacts that currently use carbon. | Hope this isn't too elementary. I am a design guy, not a process guy. | Thanks, | Paul Paul, Gold is fine for a surface finish on pads. The only concerns are the thickness of the gold plate and the application process. Electrolytic application is the process of choice.(See Earl's post on the nasty Phosphorous / Tin intermetallic) The thickness is critical from a process standpoint with regards to solderablility and and solder joint integrity. The fab house should shoot for a three to five micron coating thickness. Any more than 5 microns and you will probably incur unreliable solder joints due to gold embrittlement. Less than three microns of gold will increase the likelyhood of a void and the exposure of nickel to the ambient. Nickel is readily oxidized and is pretty much impossible to solder to once oxidized. When selecting a supplier, be sure the supplier has: 1.)Electrolytic process 2.)Process Controls (SPC and In-house Chem lab) 3.)Coating thickness measurement capability (photospectometry or x-ray laminography, etc) 4.)Batch processing capability 5.)A previously established customer base for the process you are requesting. Hope this helps. Regards, Justin Medernach

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| | | Is there any problem using SMT on gold boards? 15 years ago we were told not to use gold boards, but I can't remember why. Judging by the other postings it now appears to be common. Only problem I see is that the nickel should be plated, not electroless. My vendor wants to switch to gold to get around some problems with the key contacts that currently use carbon. | | | Hope this isn't too elementary. I am a design guy, not a process guy. | | | Thanks, | | | Paul | | Paul- | | In our process we use both carbon and Gold fingers for our switches, The biggest saving you'll see between the two is, no more carbon voids or bridging. | | The gold will also carry a longer cycle life than the carbon. As far as the component pads are concerned, we run one board that is all gold plated, and the only manufacturing issue that we've run into is the added cost...copper or nickel is cheaper. | | -Ben | | Folks, | I want to reiterate my chief concern about electroless gold over electroless nickel. I have advocated the process since its inception. I posted this objective view in the June (now archived very kindly) forum. The following reply, and personal email, was received at that time: | There has been a problem with nickel/gold plating both on PCB's as well as BGA package substrates. The problem only occurs with electroless nickel/gold plating. In electroless nickel plating, phosphorus is added to the plating baths. When you solder to the nickel/gold pad, the phosphorus migrates to the surface of the nickel, forming a very brittle phosphorus/tin intermetallic between the nickel and your tin/lead solder. If you use electrolytic plating you should not have a problem, since phosphorus is not necessary to plate for nickel with this plating method. Many of the early BGA's used electroless nickel/gold plating on the substrates solder pads. Those suppliers who are aware of the problem have switched to electrolytic plating. You should check with your BGA component supplier as well as your PCB supplier. If you have any questions you can call me at 512-933-5783. | This is more than cause for concern. Therefore, I urge us all to look more closely and deeply into this subject and the processes required to effect acceptable solder joints. | Earl Moon Earl: If the villan is phosphorous in electroless plating, then do we have to be concerned about gold thickness? Do we want to maintain 2 to 7 microns or can we go back to more traditional thicknesses? Dave F

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| | | | Is there any problem using SMT on gold boards? 15 years ago we were told not to use gold boards, but I can't remember why. Judging by the other postings it now appears to be common. Only problem I see is that the nickel should be plated, not electroless. My vendor wants to switch to gold to get around some problems with the key contacts that currently use carbon. | | | | Hope this isn't too elementary. I am a design guy, not a process guy. | | | | Thanks, | | | | Paul | | | Paul- | | | In our process we use both carbon and Gold fingers for our switches, The biggest saving you'll see between the two is, no more carbon voids or bridging. | | | The gold will also carry a longer cycle life than the carbon. As far as the component pads are concerned, we run one board that is all gold plated, and the only manufacturing issue that we've run into is the added cost...copper or nickel is cheaper. | | | -Ben | | | | Folks, | | I want to reiterate my chief concern about electroless gold over electroless nickel. I have advocated the process since its inception. I posted this objective view in the June (now archived very kindly) forum. The following reply, and personal email, was received at that time: | | There has been a problem with nickel/gold plating both on PCB's as well as BGA package substrates. The problem only occurs with electroless nickel/gold plating. In electroless nickel plating, phosphorus is added to the plating baths. When you solder to the nickel/gold pad, the phosphorus migrates to the surface of the nickel, forming a very brittle phosphorus/tin intermetallic between the nickel and your tin/lead solder. If you use electrolytic plating you should not have a problem, since phosphorus is not necessary to plate for nickel with this plating method. Many of the early BGA's used electroless nickel/gold plating on the substrates solder pads. Those suppliers who are aware of the problem have switched to electrolytic plating. You should check with your BGA component supplier as well as your PCB supplier. If you have any questions you can call me at 512-933-5783. | | This is more than cause for concern. Therefore, I urge us all to look more closely and deeply into this subject and the processes required to effect acceptable solder joints. | | Earl Moon | Earl: If the villan is phosphorous in electroless plating, then do we have to be concerned about gold thickness? Do we want to maintain 2 to 7 microns or can we go back to more traditional thicknesses? | Dave F

Dave, There are two villans if we go back to more gold as before. Gold still must meet requirements clearly indicated, as you know so well, in ANSI/J-STD-001B, Figure 5-1. If not, we're causing failure through the same old embrittlement problem. The phosphorous issue is separate, but is cause for great concern. Industry is just beginning to address it, as I've been saying, but no resolution but for alternative immersion process additives such as Boron. However, this seems to have the same effect but with a different element providing the intermetallic formation. I appreciate your addressing this issue. It was a very good question and I certainly wish to see us all get involved or the results may be as catastrophic as Y2K. Earl Moon

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| | | | | Is there any problem using SMT on gold boards? 15 years ago we were told not to use gold boards, but I can't remember why. Judging by the other postings it now appears to be common. Only problem I see is that the nickel should be plated, not electroless. My vendor wants to switch to gold to get around some problems with the key contacts that currently use carbon. | | | | | Hope this isn't too elementary. I am a design guy, not a process guy. | | | | | Thanks, | | | | | Paul | | | | Paul- | | | | In our process we use both carbon and Gold fingers for our switches, The biggest saving you'll see between the two is, no more carbon voids or bridging. | | | | The gold will also carry a longer cycle life than the carbon. As far as the component pads are concerned, we run one board that is all gold plated, and the only manufacturing issue that we've run into is the added cost...copper or nickel is cheaper. | | | | -Ben | | | | | | Folks, | | | I want to reiterate my chief concern about electroless gold over electroless nickel. I have advocated the process since its inception. I posted this objective view in the June (now archived very kindly) forum. The following reply, and personal email, was received at that time: | | | There has been a problem with nickel/gold plating both on PCB's as well as BGA package substrates. The problem only occurs with electroless nickel/gold plating. In electroless nickel plating, phosphorus is added to the plating baths. When you solder to the nickel/gold pad, the phosphorus migrates to the surface of the nickel, forming a very brittle phosphorus/tin intermetallic between the nickel and your tin/lead solder. If you use electrolytic plating you should not have a problem, since phosphorus is not necessary to plate for nickel with this plating method. Many of the early BGA's used electroless nickel/gold plating on the substrates solder pads. Those suppliers who are aware of the problem have switched to electrolytic plating. You should check with your BGA component supplier as well as your PCB supplier. If you have any questions you can call me at 512-933-5783. | | | This is more than cause for concern. Therefore, I urge us all to look more closely and deeply into this subject and the processes required to effect acceptable solder joints. | | | Earl Moon | | Earl: If the villan is phosphorous in electroless plating, then do we have to be concerned about gold thickness? Do we want to maintain 2 to 7 microns or can we go back to more traditional thicknesses? | | Dave F | | Dave, | There are two villans if we go back to more gold as before. Gold still must meet requirements clearly indicated, as you know so well, in ANSI/J-STD-001B, Figure 5-1. If not, we're causing failure through the same old embrittlement problem. | The phosphorous issue is separate, but is cause for great concern. Industry is just beginning to address it, as I've been saying, but no resolution but for alternative immersion process additives such as Boron. However, this seems to have the same effect but with a different element providing the intermetallic formation. | I appreciate your addressing this issue. It was a very good question and I certainly wish to see us all get involved or the results may be as catastrophic as Y2K. | Earl Moon

Dave, I should clarify the above by stating gold plating or coating thickness should not exceed approximately 7 millionths or the tin/lead solder will be contaminated to the extent is exceeds the ANSI/J-STD-001B, Figure 5-1, requirements. Earl Moon

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