Catching Up (Literally) with Uyemura’s George Milad at SMTAI 2016

Estimated reading time: 12 minutes

Milad: We do not have any argument there; also, we want that to be rejectable. The buyer can say, "I'm rejecting your product because...” Or the seller can say, "My product is okay because…” Everything in between can go to a lab for failure analysis to prove that the product is solderable. You can do so many things. It's not like an open and shut case. We produced this corrosion chart and we had three levels. We had acceptable, discussable and then we said, “No, we can have acceptable, rejectable, and then everything in between we're going to leave.”

We felt that it's a significant improvement. Because people used to look at one spike and declare a product rejectable. That was wrong. It would go to failure lab analysis and they’d look at the cross-section, see a spike, and end of story, it's black pad. That's why it didn't solder. There could be 100 other reasons why it didn't solder, but then you stop the investigation because you found that spike and you say, "Oh, it's black pad. I don't have to look any further.” This was a problem, and I'm hoping this corrosion chart will be a significant achievement in helping people understand the product I'm talking about.

There's one other thing that we also included and it’s something that we noticed with the XRF equipment that is out there in the field at the board manufacturing sites. Everybody has an XRF  machine and they measure the nickel and gold thickness. We found out that some of these machines are not generating the correct numbers.

Goldman: Oh, that’s not good.

Milad: Especially for very thin gold. For the nickel, at 200 microinches, if you're off by 5% and the range says 120 to 240, that's okay. But when you're looking at gold and you want to differentiate between 1.5, 2.0  and 2.5 microinches, that becomes very challenging. So we have written a section on how to verify that your equipment is working properly. It's very simple. You take a pad on the part and you sit there and read it 30 times—the same pad. Just read it and read it and read it, 30 times. Then, do the stats on the numbers that are generated. If there's too much variability, then you have a calculation now. Because your machine has this much inherent variability, reading the same spot over and over and not running around reading from panel to panel, which means your machine can only be good at this level.

For example, if you have a very good machine then 1.6 to 4.0 is acceptable. Any reading you get between 1.6 and 4.0 is the right reading and that's what we'll use. If your machine has got too much fluctuation in it, then you must narrow the range for your machine. You go to your buyer and you say, "My machine isn’t capable of 1.6 to 4.0, so instead I have to give you numbers between 2.5 and 3.2, where I know the variability of my machine keeps me in the right range.”  

I tell you, we had so much flak when we were doing this. People were arguing because you're putting the board shop guys with the compromised pieces of equipment on the spot and they must go out and buy new machines. The new machines that give good readings are in the $100,000 range. It's created a lot of flak but I think we gave them an out.

Goldman: You think you've answered everybody's concerns?

Milad: Yes. I think the way we phrased it is, "If your machine has inherent variability then you have to narrow the range of acceptability.” We inferred that would be acceptable.

Goldman: When is this revision going to be published?

Milad: The revision is in the final draft stage. Meaning it has been written and it has been reviewed. We got a lot of comments, we resolved the comments and now it is in the final draft. We are looking for a few better demonstration pictures. Gerard O’Brien is working on that, very extensively, to try to put some illustrations in there that are meaningful to the people using the specification.

We also had to reconcile with IPC-6012, which spelled out acceptability criteria and methods of sampling for process control. The way we did things was a little bit different. We had to resolve it, and it was resolved. I wasn’t at that meeting but Gerard OBrien worked with the 6012 committee  and they've come to an acceptable way of writing it so that 6012 is satisfied and the 4-14 subcommittee is satisfied. It's ridiculous to have conflicting  recommendations from committees operating under the same organization.

Goldman: Now you must be about ready to go to final approval. Is this where it goes out to the membership?

Milad: We're getting ready for what we refer to as going to ballot. We had the draft and we had the peer review. Now we have corrected everything and then it's going to go to ballot and hopefully it will be out before the end of the year.

Goldman: Wonderful.

Milad: It's a big achievement.

Goldman: It certainly is. Now, you still have a third presentation tomorrow afternoon, correct? A third paper?

Milad: Yes, our technical director, Don Gudeczauskas, has done some research and put together a paper that was accepted in SMTA but he had other travel plans. So I am presenting the paper for him, and that's challenging, because I must get into his mind and see how he laid it out and what message he wants to deliver. I've been talking to him every day now to make sure we're on the same page.

His paper is interesting because he was looking at three different types of gold over nickel and palladium. He referred to them as standard immersion gold, high efficiency immersion gold and “reduction-assisted immersion gold,” so three categories. Two of them are immersion golds, and immersion means it is an exchange reaction. Nickel goes into the solution and gold comes out of the solution. Then he had a third gold he referred to as reduction-assisted immersion gold. It is a combination immersion and electroless deposition process. This immersion gold is more active at the initiation of deposition; the electroless reaction is continuous throughout the deposition process. It does not corrode the underlying nickel.

Goldman: Very interesting.

Milad: He was presenting data on the solderability of these three types of gold on nickel, and the solderability of these three types of gold on nickel palladium. He did ENIG and he did ENEPIG  in an effort to differentiate between them.

He pushed some parameters to see a difference. One of them being, staying in the gold bath too long, because then he can create some corrosion so he sees if there is a propensity to prevent corrosion. It's an interesting paper. The differentiation was in the degree of nickel corrosion in both ENIG and ENEPIG. I think it makes a case for the reduction-assisted immersion gold bath as a better alternative.

Goldman: You might have a little more leeway with it.

Milad: Yes, it doesn't go after nickel as readily as an immersion gold bath would.

Goldman: Exactly. Well, George, it sounds like you have yourself a few very busy days here. Thanks for taking time to stop by.

Milad: Thank you, Patty.

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