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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Profiling board

Yngwie

#20042

Profiling board | 23 May, 2002

Hi guys...

Has anybody hv an experience with using a common or standard profile to reflow high mix brd ( say, low, medium and high )?. The reason for asking is that, we are running high mix low volume, and materials that were consigned is exactly as per ship request. Thisis the trend to come. No more luxury of having loaded board to create dedicated profile for the product to be ran. With this takes place, I think the only way of doing this is to have a common profile. An added advantage to fast changeover. But now, the customer was asking me on what makes me think that products A, b, C can be reflowed under medium profile, where product D,E,F is running under high profile ? How do I catagorised them ? What I did was the similar mass brd, will be categorized under the same profile. the answer is not acceptable...can some one help me on how to handle Material Kits consigned = qty to be shipped, & how you guys deal with this situation.

Help is very much appreciated.

cheers, yngwie

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#20043

Profiling board | 23 May, 2002

One thing I have done in your situation is ask the customer if they have any older design boards that are similar in thermal mass or if they have any from proto work, etc.... Otherwise find/make a board of similar thermal mass as best you can.

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#20045

Profiling board | 23 May, 2002

Well it depends on what kind of oven you have. If you have a short oven, you are going to have a difficult time. You will probably end up having several different profiles if that is the case. We have 3 BTU TRS 212 furnaces. They are fairly long 8 zone furnaces. By having a long oven your are able to stabilize large mass differences across the boards quite easily. The reason being is that there is a lot of preheat, and everything has time to come upto temperature before you hit reflow temperatures. We had the same question "Can we use a common profile?" My answer was yes, and the way I proved it was to take a very thin .030" and a very thick .115" thick backplane board and profile them. I also took a 4x4 .100" thick copper slug and attached probes to it. The profiles were all very similar to one another.Ramp soak and peak were right into spec. The only difference was of course the cool down. I think that there was just an article in SMT or Circuit assy. magazine about this very issue. I believe they said that you should be profiling every board, you should so you can show it to your customers, but I do 100% feel that it is totally acceptible to run a common profile. I proved it. It is going to be dependent mainly on your ovens.Break out the ol' thermo couples and check it out !

Hope this sheds a little light.

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JohnW

#20046

Profiling board | 23 May, 2002

yngwie,

are you getting a wave from the customer to say it's not your fault you fried the parts? Profiling's one of those things that is a pain to dobut it's one of the most important factors in the assembly processes. I've read and seen instances where 'standard' profiles are used for all of production but I've never been convinced. One theory is that you use the mass of the card (with all the components ) to select the appropriate profile, all well and good but what if your card is say 300mm by 300mm with very few layers and a handfull of components, but by coincidence has the same weight as a sma say 100mm square rogers based PCB with lot's of chips or stuff on it, do you use the same profile?, probably not since the rodgers will sink a heck more heat. Other things to consider is the style of component you placeing in term's of the IR effect, you could have 1 PCB with all the same style components that are black boddied then another with silvber / white bodied parts, different IR uptakes and depending on the oven your using that could be anything from 10 - 20deg C of a change. I think it's important that the customer or people asking for you to manufacture without a profile card be made aware of the downsides and the lack of control that they are introducing into your process. There are system's on the market that help simulate this and get round the problem, there's oen mentioned on the forum at the moment, have a read of that but you still really want to verify that what your needing is waht your getting on the board and at critical components.

Summary, personally not something I've want to do, but if orced I'd be making sure I had a bit of paper saying they understand the risks.

JohnW

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#20047

Profiling board | 23 May, 2002

One more thing I want to add. Don't turn this into some big deal. Its not atom splitting, or black majic.Bottom line is that you are going to be doing some experiments to prove it to yourself and whomever else requires the data. Profiling is time consuming and a pain in the a$$, but its all part of the SMT process.

Try what I mentioned in the above post.If you have a short oven don't even attempt it, because it is not going to work. We had a little ABW oven and it was not worth a crap, we had like 50 profiles in it.

By the way there are a ton of those old BTU 212 ovens on the used market for super cheap. They work very nice, but the older ones do not have any type of flux management system in the cooling section, so you have to keep them scrubbed down.

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#20048

Profiling board | 23 May, 2002

There are instruments from ECD, KIC and Datapaq that are used in addition to classic profiling for oven thermal management and they also have some very efficient prediction software for profiling. I am not an advocate of common profiles. Most boards are unique and should be treated that way and have thier own profile. Soldering is the most critical process in your operation.

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Yngwie

#20056

Profiling board | 24 May, 2002

Pete C, Cyber wolf and JohnW...cheers man...excellent input.

But I 'm eager to try the method mentioned by Cyber wolf..sounds very convincing. Let see what is the results later.

thanx again and have a nice weekend.

/yngwie

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#20066

Profiling board | 27 May, 2002

One thing you should do is characterize your reflow oven, run profile boards of various densities, say 2 gm/sq.in. to 10 gm/sq.in. Adjust the oven settings for these various boards to acheive your standard profile based on your solder paste manufactures suggested profile. Once you have a standard profile for all the different weight boards (the more boards the more linear your set up chart will be) you should be able to set up one or two standard profile oven settings and then vary the belt seed to acheive the proper profile. Then set up a chart that will allow your operators to weight the board fully populated just before it goes into the reflow oven, match the gm/sq.in. on the chart, and set the belt speed according to that chart. Works great.

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harotec.ch

#20073

Profiling board | 27 May, 2002

Hi Yngwie Have you got a reflow oven yet. If not, forget about complicated profiling with test runs or reflow trackers. We've got a nice oven with integrated temperature-feedback system. You build any profile you want and the oven will adjust its heating elements during each and every soldering cycle. Our oven "Ecolsold 350 Superior" is ideal for small to medium runs with complex boards. The problem CyberWolf mentions with the short ovens we solved with a single chamber system. As we want to control the entire reflow process as measured on the board this is the only way of securing control over time, place and temp. Have a look at our website at http://www.reflowsystems.com and especially at the second article in http://www.reflowsystems.com/Press/PressReleases.pdf

If you already have a reflow oven and want to stick with it, good luck with tracking, testing ... Because in the end PeteC and JohnW are right: "Soldering is the most critical process in your operation."

Lothar

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#20214

Profiling board | 4 June, 2002

I have the same problem. I made 3 standard profiles on a 6-zone oven, but always advice to make (or at least verify) a profile. But if customers don't want to, I point at the risks, and choose a slightly higher profile to be on the safe side. If you are using IR oven instead of a Forced convection, I would advice always to verify.

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reflow oven profiler