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When does SMT inspection/touch-up become rework?

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When does SMT inspection/touch-up become rework? | 20 January, 2011

Because we build Class 3 assemblies, our company has formal inspection steps on our routes. CCA's go through surface mount and then an operator inspects the solder joints for defects and corrects them (touch-up). Following this they go to formal inspection. If they catch everything there should be no defects found at formal inspection. If so, they are kicked back to the operator for rework. We do not own any AOI equipment and run high mix/low volume products.

Ideally a board should come off the reflow oven and go right to formal inspection without any defects. Since we live in the REAL world, should any touch-up that is performed count as rework and logged that way for accounting/quality purposes or should any touch-up be considered part of the job and be counted as assembly time (not rework)?

Secondly, it bothers me that we are performing "double inspection" on all of our CCA's, but it may be worse to formally inspect them right off the reflow and have every nonconformance logged and returned to SMT (movement and waiting waste). Almost all CCA's would be returned. However this would be one way to "force" the collection of defect data which is what I need to optimize our SMT process.

I recently ran a test and found that the SMT operator/inspector notes 5-10 times as many defects as our formal inspectors do which is over-processing waste. This may be another reason to eliminate the "pre-inspection/touch-up" step. I would be interested in knowing how other companies approach these issues. Thank you in advance.

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When does SMT inspection/touch-up become rework? | 20 January, 2011


In a previous life, boards came off of the machines, and went to SMT QC, then to SMT T/U before heading off to wash and through-hole. The concept being that the SMT "team" was responsible for the quality coming off the machine, with QC and T/U thrown in there to counter reality. This allowed (theoretically) early detection of assembly issues which could be fed directly back to the machine operator, and minimized (near eliminated) any bad blood between the thru-hole assembly folks and the SMT assembly folks.

My current shop is quite a bit smaller, and, as such, my SMT t/u folks are the same folks that perform the thru-hole assembly. So, my process is pick/place, SMT insp/t/u, thru-hole, final QC. We've found that this gives us the best speed of processing, with the best opportunity of catching defects prior to final QC.

In both of these instances, I consider these qc/t/u steps to be a part of the assembly process, though we do log the defects as part of the quality process. Sort of a step serving a dual purpose.

I agree with you regarding the "double inspection," however, my experience shows that the real world ends up requiring it. Sending items to formal inspection and logging them all, while valuable for nailing down process issues, could overwhelm your rework operations. If you go to a "formal" inspection, then kick them back for rework, then send them to another inspection to verify the rework has been completed, you are, essentially, performing the double inspection anyway. I've found that doing it up front is faster for the process than doing QC before and after rework. Of course, your mileage may vary.

Over inspection is another story. In a previous life, we discovered that all of our inspectors and rework operators were doing Class 3 work...even when the contract requirements were only Class 2. We discovered that this was a huge waste of money/time. The fix was to re-educate everyone on the actual requirements, and to involve them in the process by teaching them what the overworking was costing us. I would guess that the same goes for your class 3 jobs....introducing them to the concept of overwork, re-educating them on the actual requirements, and spot checking what they're doing. A word of warning, though, this approach will generally lead to a lot of question asking for a little while, while the people get used to the new methods, etc; they'll tend to want to over-do the double checking until their attitudes about being questioned start to diminish.

cheers, ..rob

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When does SMT inspection/touch-up become rework? | 25 January, 2011

I understand what you are asking. I just wanted to ask if you or your company has considered purchasing an AOI or ICT? Perhaps both? Both are valuable tools in the manufacturing process. We lived without our AOIs for quite some time, but in my career, I have never been without an ICT. An ICT will redistribute the work down-stream, but it will test the board much faster than a human inspector, plus it will catch things that would be impossible otherwise. I don't know exactly what the IPC standard says regarding inspection of Class 3 pcbs, but does it have to be done with a human, or can it be done by some other means? If so, you could probably eliminate one of your inspection points and replace it with either an AOI or ICT. It sounds like you may have budget constraints, so an ICT would probably be more viable. You can get used systems for a fraction of the cost of a new system ($12-40K) depending on what type of testing you need to do. If you need sources, I can help you with that as well. I am not a dealer or a sales person.

Reese, CLAD Test Engineer

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When does SMT inspection/touch-up become rework? | 31 January, 2011

You stated that you are producing Class 3 boards so I assume you are familiar with the IPC standards.To answer your question directly, I'll refer you back to the J-STD-001. Clause 12.1 states "12.1 Rework Hardware defects shall [N1N2D3] be documented before rework. Rework for Classes 1 or 2 should and for Class 3 shall [N1N2D3] be documented. Rework includes hand solder touchup after mass soldering operations."

By that statement, any time a soldering iron touches a solder joint after the joint has been formed is rework. There is a stated exception that reapplying solder or a second application of solder in a single hand soldering application i snot rework. BUT, the process you describe is plainly called out in J001 as a rework operation and, since you have a class 3 product, SHALL be documented and dispositioned.

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When does SMT inspection/touch-up become rework? | 11 February, 2011

Thank you for all who read this with interest and especially those who replied. I have considered the points posted and here is what we came up with:

We all agree that double inspection is a wasteful operation especially if the operator is more critcal and t/u more than required. Therefore we will let our formal inspectors inspect and any defects will be sent back to SMT for rework. The operator will glance at each board off the reflow, noting any gross abnormality that must be addressed immediately and to remove solder balls before cleaning.

Kris is correct in saying that all defects from reflow must be documented for Class 3. Formal inspection has been much more cooperative in documenting defects than assembly so inspection will keep a record of defects and the data will be at my disposal in order to improve the process.

Even though there is more travel involved and possibly more lead time, we feel we are still way ahead from a labor cost perspective and are willing to accept the tradeoffs.

Lastly, I would really like to use AOI either in SMT or in conjunction with formal inspection if the budget allows at some point. Any additional comments on this topic are appreciated.

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Metcal soldering rework