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AOI, Pre or Post Reflow?


FD

#23719

AOI, Pre or Post Reflow? | 8 March, 2003

We are trying to implement AOI into the mix.

One PE wants it Pre-Reflow, to catch and fix the PnP screw ups and the other PE wants it Post-Reflow, because the oven will fix quite a bit of placement offsets and mainly to catch any problems that the Reflow may introduce. And he says that Post-Reflow AOI will eliminate the need for a real person QA check, so less board handling and labor costs.

But I say fix the profile so the oven is a non-issue and put the AOI pre-reflow. This way I can be sure that my PnP investment is up to par.

Although, I have been to numerous other CMs and some OEMs and close to all of them that have AOI have it post-reflow.

I can see that if you need 100% board inspection, and the AOI can not keep up with the production line, then post reflow is the only option.

Is there a right way to go about this? Get two AOIs - one pre and one post? ;)

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#23723

AOI, Pre or Post Reflow? | 9 March, 2003

So, where do your parento charts indicate the largest problem?

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Neil

#23724

AOI, Pre or Post Reflow? | 9 March, 2003

I agree, with Dave what is your top 3 defects and what causes them? Most post reflow defect are already on the board before they go into the oven, all the oven does is expose them.

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#23733

AOI, Pre or Post Reflow? | 10 March, 2003

Most pre-reflow AOI systems today can easily keep up with production line beat rates.

Pre or Post reflow AOI is the difference between process control vs. defect screening, in my opinion.

Pre reflow repairs cost much less than post. Pre AOI is for finding SMT line errors in real time. Also, they can trend placement accuracy- if the pre reflow AOI has component X-Y-Theta measurement capability. The purpose of pre AOI is to identify the problem in real time, you then fix it and prevent it from occuring again.

If you have a solderpaste measurement system for post print inspection (less cost these days $15-35K), or a printer with post print inspection capability and pre-reflow AOI, boards can be sent into the oven with greater confidence.

There are oven management systems from ECD, KIC and Datapaq to ensure your oven is executing your profiles accurately.

Post reflow AOI tends to be more about defect screening. These systems tend to be off the line. Boards are sent into the AOI many minutes, hours or maybe the next day after assembly reflow soldering.

From my experience, a vast majority of SMT solder defects found in post reflow AOI are directly associated with a paste deposition or component placement problemo.

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MA/NY DDave

#23738

AOI, Pre or Post Reflow? | 10 March, 2003

Hi

First of ALL, Thanks.

I am first coming into this from the outgoing inspection or customer receiving inspection side of things.

Well not really, or fully.

Yet it will catch defects and add to what the final scanning outgoing inspectors find. Basically at this point in time AOI is a human final QA aid, yet not a full crutch.

< From PeteC < Now Pete gave some really good thoughts, yet I only < will point out one. <

Well put by Pete    

< One final comment That is your choice, and depending on your operation and what you have in place it might be the right choice. If your PnP is that troublesome I would do something like you have chosen or investigate an alternative.

YiEng, MA/NY DDave

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MA/NY DDave

#23761

AOI, Pre or Post Reflow? | 11 March, 2003

Hey Frank,

We got lucky.

An article just appeared in one of our industry's magazines. Now you still have to read these articles carefully since the proponents sell the equipment yet it does support both opinions.

Except it says (before PnP) and (post Reflow) are the best places. Again I would use your own judgement and maybe fix something if after PnP works better for your operation.

The current magazine March isn't up yet on the web. The title is Unlocking the power of AOI

http://smt.pennnet.com/Search/index.cfm?Section=Archives

YiEng, MA/NY DDave

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FD

#23773

AOI, Pre or Post Reflow? | 12 March, 2003

Thanks, good food for thought.

Trying to get prep'ed to go to APEX in a few weeks and see some AOI demos...

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MA/NY DDave

#23775

AOI, Pre or Post Reflow? | 12 March, 2003

Hi

Thanks,

Going to APEX to see personal demos and hear what they offer and recommend is a great idea. I mean if you want to put AOI everyplace I am sure you will be supported with open arms.

What I found interesting in the article was that large Asian CEMs (CMs) were using AOI to assist cost control via process control and feedback post paste, pre PnP.

The other thing I hope you will read is that pre PnP AOI can be deceiving since as you go through reflow the components will move due to the soldering process. This to me would mean you would have to carefully program the vision system to not have false rejections.

YiEng, MA/NY DDave

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