Profiles in Courage

Circuit Technology Center’s Sal Moxy and the Circuit Board detectives.

Chapter 1: The Problem

"Why do you need an extra board to do a BGA rework profile anyway? I’ve had millions of different types of through hole and surface mount parts placed on boards and the rework people never said anything about a profile board. Sound like a scam to me."

Sal Moxy the customer service engineer from Circuit Technology Center had heard this approach to BGA rework before and Mr. Lars D’Arce, the hard edged buyer from Inexpensivo Technologies, was going to make him hear it all again in spades. "Yes sir Mr. D’Arce but….":

"Look" D’Arce said with his nasal rasp grating on Sal’s already tender nerves, "All you gotta do is heat the thing until it reflows and then stop. How hard is that? And extra components, what do you need those for? Do you think they grow on trees? You guys must think I was born yesterday."

"No. No Mr. D’Arce, that’s not it at all. It’s just that BGA components are a little different." Said a slightly exasperated Sal trying to get D’Arce focused back into the actual details of BGA rework.

"Different! Different! Look sonny boy, I’ve been working in this industry for 25 years and soldering is soldering. You take eutectic solder, you take 183 degrees centigrade, you use a little flux if you need it, and you solder the part to the board. All you guys who try to make it much harder than that deserve the trouble you get into."

For a pre-internet guy Mr. D’Arce was made for raving. Sal pictured him at one of those techno clubs in Montreal dancing up a storm and banging into anything that moved. Or maybe as one of those Internet chat room freaks that ranted about "idiots" and conspiracy theories. Those visages took a little of the edge off of his response. "Well Mr. D’Arce, it looks like we won’t be doing these four boards for you but if you want an explanation of why we approach BGA rework as we do you can go to our web page at http://www.circuittechctr.com/services/bga.shtml, you never know, you might change your mind."

"Yeah, right. Well, look Sal, you’ll have to forgive me if I go to Chou Wou Wahs Chinese Restaurant and Rework for this one. I thought I’d give you guys first shot since you’re the experts and everything, but Chou will charge half the price. Yeah, I know he doesn’t go in for all that ESD bull and he doesn’t have those high priced BGA rework machines, or x-ray but he knows soldering and that’s all that matters." Said Lars D’Arce with finality.

"Oh well. Ya gotta do what ya gotta do Mr. D’Arce. Best of luck and don’t be afraid to give us a call if we can help you with anything." Sal didn’t want to burn any bridges. You never knew in these BGA cases. What he did know was that sometimes the most adamant non-profiler became the most religious convert when it was all over. If that was going to happen he didn’t want to make the conversion more difficult than it had to be.

In another part of the universe:

In the Training Center of Circuit Technology Center Niles Nutmeg the Company Trainer wrapped up his session on BGA profiling with a quick question and answer session.

"Jeanie" Niles asked in his high-energy style, "Why do we need an "engineering" board to conduct a proper profile at a BGA location?"

"Niles I can hardly count the ways." Said Jeanie N’Abtl as she was swept up excitement of mastering a subject. "I’ll give you an example Niles of a BGA component with 600 balls. Even 99.8 percent success isn’t good enough to guarantee proper reflow of the part. You have to do much better than guess if you want to get it right. Whether you thermocouple the board and run the profile that way or work the old trial and error method you will have to bring the site through one to five heating cycles and that should be avoided on an operational board if at all possible."

"Jeanie. I knew there was a reason your company sent you here. You are a super star!" The whole class applauded in semi serious delight. "Now what about ‘engineering’ components? Why would they be necessary?" Niles said as he further focused the class on the particulars of profile development."

Ishtar Ibn Imbibn seriously raised his hand and glared at Niles. Niles was surprised, as Ishtar had been reticent to this point, so he chose him to answer the engineering components question, though he wasn’t sure what he’d get. Ishtar was right on and ready as he stated with proper deliberation. "Niles, it is impossible to make a proper determination of the projected condition of the solder balls after they have been reflowed several times in the profile development. It is best, when one has determined that the proper reflow cycle is attained, to take a fresh component and observe the condition of the newly reflowed component. Only then can one feel confident that the thermal cycle is proper. Do I have this right Niles?"

"Woah Nelly Ishtar, you couldn’t have it righter. That is fantastic. I’m so glad to see that you have complete command of the subject." Niles added seriously as Ishtar beamed with a growing confidence in his grasp of the subject at hand. "OK class, now let’s take it to the next level. I’m an experienced BGA rework engineer / operator, I have the best system and I have good visibility on a new component and board. On top of that, I have a hundred profiles stored in my machine, several of which I know can be used with this component. What’s the big deal? Why all this profile board and engineering component mumbo jumbo. Aren’t we just wasting people’s time and money?"

"What if the board and component are multi thousand dollar units? Why would you take that risk?"

"What if this component has a ground slug or there is a serious ground plane at that location that causes most but not all the balls to flow and you don’t find out until you’re done?"

"What if the board is especially sensitive to heat and warps and you’re not ready and the component shorts?"

"What if the component curls on the corners and you didn’t take any special precautions and you lost the component?

"OK Folks, I think you have the idea." Niles said with the satisfaction a teacher gets when his students are truly plugged in.

Ishtar chimed in "You know Niles, after what you have told us I cannot believe anyone would proceed to rework a BGA location without the proper engineering boards and samples."

Niles paused for a moment wondering whether to handle this issue just yet but there was still a half hour left in the class time and he felt that this group really had grasped the essence of the issue at hand so he gave them some more to think about. "Well, Ishtar, I know that in your company, Explosive Concepts, things are done right. That is the expectation of the military who is your primary customer and of everyone in the company. Part and parcel of that is the money allotted to ensure things like profile boards, engineering components and the individual profiles themselves, are properly acquired. That isn’t the case in many companies that must operate with closer margins, tighter budgets and greater time constraints. The pressure on them perpetuates a risk taking environment."

"Still it isn’t right." Ishtar insisted.

"Yes it’s hard not to agree with you there. Whenever possible we should insist on the proper materials to conduct a profile. If they are not available, everyone should be made aware of the risk involved and then proceed with caution. Before the end of the class, one of the last things I will show you is how to best approach a situation like that."


Chapter 2: The Wayward Lamb

Lars D’Arce had four boards that he had to put upgraded processors on at the request of his customer. These processors were BGAs. By design he didn’t have the capability to put those on the boards himself. He subbed all that stuff out. He didn’t want to have to deal with all the people he would need to hold around to do that sort of work. He had called his friend Sal Moxy at Circuit Technology Center, but Sal went into this whole rigmarole about profiles, profile boards and engineering components. For God’s sake, Lars only wanted the components reworked not the story of Western Civilization. He went to his second option Chou Wou Wah’s Chinese Restaurant and Rework. He waited in the back as Chou came in from the kitchen wiping his hands on his apron and changing into his white electronics looking jacket. "Oh, Mr. Lars. Nice to see you."

"Hey Chou, great to see you too. Look I have a favor I need to ask. I have four boards I need you to rework as soon as possible. I’d like to get them back tomorrow. They’re BGA’s."

"Sure. Sure." Chou said while trying to get a handle on what type of work was required. He saw Lars once a month or so and one-way or another they were able to communicate, and get the work done. Usually the work required was simple wiring or component placement – just perfect for he and his wife Wen who was the real talent of the operation. Over the past three years they had forged a solid relationship with Lars.

"Look, here are the components, BGA’s, can you do BGA’s?"

"Sure. Sure" Chou looked at the components Lars was pointing to. "Where are the leads?"

"They’re under the component. Look, hold it up like this you can see them under there. Are you sure you can do this?"

"Oh, yes I see. No problem. Can you show me the new component?"

"Yeah. Yeah right here. Look I ain’t got any extras so you have to get it right the first time. Understand?"

Unfortunately, Chou was beginning to understand. He started feeling a little sweat come to his brow as he grasped the situation. "No extra parts? What happens if something goes wrong?"

"It won’t. Anyhow, we’ll handle it then."

Later the next day……

Lars’s cell phone rang while he was winging down Route 495. "Hello." He shouted over the noise of his late model car that wasn’t as sound proof as it used to be."

"Hello Mr. Lars. I’m sorry to tell you, but I have problems with your boards."

"What do you mean?" an exasperated Lars intoned. "I thought you said you could do them."

"The part won’t sit flat and the board wants to burn all up. I don’t think I can do this. This is big trouble for me." Chou felt as if he had been set up and was a little frustrated himself. He just wanted to be rid of this headache as soon as he could. He had had his wife Wen, who has a great soldering touch give him a hand but they still couldn’t get anywhere with these strange parts.

"Alright, I’ll be there in an hour. Just hold on." Lars knew he had trouble now. Two days had passed, he hadn’t completed the job and it sounded like he might have some scrap on his hands. Dang! How could this happen?

The scene with Chou was none too pleasant. Chou was defensive and agitated. Lars was in aggravated attack mode. There was nowhere positive for this to go. As the conversation proceeded it became animated and it was unlikely either party understood much of what the other was saying. It was clear they each thought the other was at fault and they became more stubborn the longer the exchange lasted. It all ended with Lars leaving with his four boards in hand. One was browned pretty badly with the coloration you would desire of a roasted marshmallow. All four components had been used up and there was a second board with a lopsided looking component on it. Lars didn’t even wonder if it would work, there was no question that was screwy too. Chou had shown him the equipment he had used. Something that looked like two high-powered hair dryers aligned top and bottom so that the board and component would sit in between. Chou had talked about the new component sliding around and not staying in the location it was placed and how impossible it was to line up the little balls to the pads looking at it from the side, even with a microscope. Now Lars’s goose was cooked. No more components (gone at $125.00 a pop) and one of his customer’s boards was potentially ruined for good. Stuck, stuck, stuck!


Chapter 3: What to Do Now?

Lars D’Arce was in a fix. In a fit of hurry up mixed with a faint spell of false bravado he had blown off the sage advice of Sal Moxy, the customer service engineer from Circuit Technology Center and had his four BGA processors and boards reworked disastrously by Chou Wou Wah’s Chinese Restaurant and Rework. The whole thing was out of Chou’s line of expertise, but Lar’s had been busy, preoccupied, under a heck of a lot of pressure and not ready to listen to the litany of details involved in BGA rework. Now as Sal had warned he was paying the price. God, he hated eating crow, but if he had any chance of getting out of this mess he was going to have to go back to Sal and his gang.

When Lars called CTC, Sal was on another line so Lars (in his typically friendly way) demanded to speak to Carlos, the company expert in BGA’s. Lars knew Carlos was as edgy as he was, but Carlos would get straight to the point and not dance around like those goofy sales types. When Carlos got on the line Lars, to his credit, gave Carlos the whole story.

"Holy smokes, Lars you may have a pretty costly problem on your hands. The only thing I can hope is that, with Chou’s general knowledge of boards and components, the damage done is mostly of a cosmetic nature. The guy works the low end of the market, but he’s no dummy." Carlos said while he tried to sort out the best way to handle Lars, his boards and this situation. As knowledgeable as Carlos was with BGA’s he knew that all the niceties the Sales force used permitted them to handle this stuff with aplomb. Aplomb with people was not what the ‘C-Man’ was known for. "All I can tell you Lars is that you should bring the boards in here so that Giddy the salesman, Sal and I can look them over. Then we can give you some kind of idea of what we might be able to do."

Well then, Lars would have to go up and face the music. Ah, what the heck, he knew these guys wouldn’t stoop to make him feel like a fool (which of course he would have done in a second if the tables were turned). He walked in to CTC to be effusively greeted by Giddy, who made some small talk about Lar’s and Giddy’s kids, cars etc. while Sal got freed from the phone to come up. They fitted Lars with the appropriate ESD garb, heel and wrist straps, made him test them, then walked to a well lighted bench to take a close look at the boards. Carlos came over as soon as they had the boards laid out. He quietly looked at all four boards. "Well that’s good, at least these two are unaffected." He looked at the two components that Chou had attempted to place, but had taken off the boards. "On the surface, these don’t look any worse for the wear. Does your customer have an opinion about reballing?"

"Yeah, said Lars. The customer doesn’t mind the ones you say are ok being reballed and used as spared but he’s making me split the price of the screwed up parts. We’ll have some in tomorrow." Oh it hurt to say that! "Further, the only reason he let me keep the job is that I told him I’d go to you guys and I also told him all the stuff about how to profile properly. I really had thought it was a bunch of crap, but obviously, I have seen the error of my ways."

"Well, to be fair," said Sal "Most of us have had to learn hard lessons about the rework of BGA’s. They are just so different from components that display their leads for hand soldering and observation it’s a quantum shift in understanding." Sal didn’t mind at all dealing with the kinder gentler version of Lars.

"I do have a little bad news for you though." Said Carlos. Grabbing his large hoop earring with his left thumb and forefinger. Everyone’s stomach collectively clenched to hear this. "The overcooked board shouldn’t be a working unit. It’s really seen too much heat. It’s impossible to know what kind of damage had been done by those thermal excursions. On top of that, even if it’s going to be used as an engineering board it will probably require some repair to the dog bones and some pads."

"You won’t believe this." Said Lars with surprising joviality, "But I already discussed this with the customer and when they heard the whole story they said we could use that board as a profile board and if it still worked when we were complete they’d use it in the lab. But I have to ask, what is a dog bone?"

Carlos grabbed the nearest sheet of paper and proceeded to draw the typical BGA pad to via structure. The form had a clear resemblance to a barbell or a dog bone / biscuit. "Let’s say that one end or pad of this structure is the BGA pad, where the ball meets the board. There is a controlled amount of solder per each pad or ball. Without this control the solder will either bridge or create an open. It has to be just right. What keeps the solder in place on the pad is merely a neck or dam of solder mask on the handle or middle portion of the dog bone. When that breaks down, you may lose critical solder volume on the pad or some nearby ball may bridge to that location. Solder mask under the component serves a compelling function." Explained Carlos with intense focus on his drawing.

"All right," sighed a resigned Lars. When will I know the extent and expense of that condition?"

"Once we’ve removed the component. You can come by to look at it or Sal can give a call with the evaluation when we’ve gotten that far."

"You know, at this point, this thing is in your hands fellows. I have to trust that you won’t take advantage of me thought it truly pains me to do so."

"Oh Lars," piped in Giddy "When have we ever taken advantage of you."

"Every time you charge me a dollar, you highway robbers!" Lars growled, paused and then laughed as he saw the downward drooping faces of the gang. "Come on fellows, I’m just kidding for crying out loud. I trust you. I’ll breathlessly await the gouging call of either Giddy or Sal."

For more information on mask touch up at "dogbones" click here.


Chapter 4: The Profile and Attempted Placement.

Mr. Lars D’Arce had presented Circuit Technology Center with a bit of a challenge. He had given them four boards that required one 600 pin BGA per board to be removed and replaced. There were a few extenuating circumstances. D’Arce had previously given the boards to Chou’s Wou Wah’s Chinese Restaurant and Rework to do the work. Unbeknownst to Lars and Chou this kind of rework was a little beyond what Chou was currently capable of doing. One of the boards had clearly been cooked to an attractive caramel brown and all four components had been deballed in an attempt to place the components on the boards. On top of that there was no profile board or extra components to develop a proper thermal profile for Mr. D’Arce’s board / component location.

In the BGA area Carlos Banjo the thirtyish, hair thinning, pony tailed, ear ringed, intensely focused, rail thin, dangareed and occasional cigarette smoking BGA guru of Circuit Technology Center was contemplating his options. Lars’s customer had provided CTC with four more BGA components to place on the board and allowed CTC to reball three of the previously placed components to be used as spares. One would be used to test the profile, one would be used to ensure the profile worked in reality as the temperature data said is would. Hopefully that gave them enough components to develop the profile, check the placement and have a spare. Time would tell. The traditions of profile development on BGA rework machines wasn’t that old, but the way technology moved these days it seemed to Carlos as if they had been doing this stuff for eons. Originally, the machines available to rework were only capable of repeatably reworking the simplest devices on smaller boards. Rework machines of any era had a daunting task. They were supposed to be able to repeat the original thermal profile of the circuit board the same way as when the board was totally immersed in a reflow oven. During initial assembly the whole board is brought up to reflow temperature at the same time in a controlled environment. Not that there aren’t problems inherent in that process, but trying to heat and reflow (rework) a confined spot on the board (as opposed to the whole thing simultaneously) while not warping the location or screwing up adjacent components took the rework machine manufacturers a few iterations to get right. The process was still one that took more operator skill than most people felt comfortable relying on (especially for the short runs). It also took someone who could operate a computer, had soldering skills, and understood solder paste and screening. It was an expensive operation. Early on, there was only one generally accepted way to create the thermal profile for components to be reworked. That was to drill holes from the bottom side of the component in three to five locations and have a thermocouple terminate in a solder ball under the component (often a practical impossibility). Several other thermal couples would be placed on top, bottom and around the reworked site. Information would be gathered and out of all this an acceptable profile would be developed.

Currently accumulated time and experience have permitted and / or forced rework engineers and technicians (depending on their environment) to significantly reduce destruction and development time. Even though drilling through a board and placing a thermocouple directly in solder balls is a desirable method of attaining a look at thermal profile of solder balls on the inside of an array, it is often an impractical solution. Time and the unavailability of extras of anything forced other considerations. In general the compiled history of BGA experience and the real time information gathered by observing various components’ reflow provided rework personnel with rules to go by. Additionally, attaching thermocouples to vias on the bottom (these were through the board vias) presented other critical information as well as the use of small mirrors. Finally precise inspection optics and real time x-ray could give the engineers enough information to make a reasonable decision about the quality of a given profile.

In the instance of Mr. Lars D’Arce’s boards, the component was one that Carlos and his technicians had long experience with. They had several profiles already developed for that component with similar board sizes. Even though it wouldn’t be exact, they knew they would be close. They would have two people view the placement cycle and they felt confident they could do this profile with minimum impact on the development board. Unfortunately, as Carlos had predicted, there was some mask damage under the component when the browned board’s component was removed. On the other hand the skillful technicians at Circuit Technology Center were able to directly correct that problem by using one of their proven repair procedures. In the end Carlos was able to present Lars with his reworked boards and a spare component. He was even able to demonstrate to Niles Nutmeg’s BGA class this quickstep approach to profiling. It was a beautiful thing.

It was late afternoon when a grateful Mr. Lars D’Arce arrived to pick up his boards. "Well Sal all things considered I got out of this one pretty lightly. I must admit you guys saved me."

"That’s what we’re here for Lars. All well that ends well. I guess we’re all the wiser about these pesky BGA components now." Said Sal graciously.

"Right. Now that I’m over the shock factor of how different these things are to rework than other components I’ll know how to proceed with the upgrade process when it involves these things."

"Roger that, hope everything goes well with these. See you around."

In another part of the universe:

As the BGA Rework class drew to an end, Niles Nutmeg could proudly look over his class and know that they had the fundamentals of BGA rework down pat. They had seen how to do things right and had seen what can happen when things go wrong. Even though his most intense students Jeanie N’Abtl and Ishtar Ibn Imbibn seriously had issues with the way some people seemed to cut corners with profiling, they were much wiser for the experience. Niles reminded them "It’s good to know what’s happening on the other side. You never know where you’re going to end up in this business."

Ain’t that the truth.

Note: Many of the names have been changed to protect the innocent and the not so innocent.

Several members of the Circuit Technology Center team contributed to this feature story.