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Solder Paste Inspection System.

nightbull

#19011

Solder Paste Inspection System. | 28 February, 2002

I would like to know if there are any IPC standards or anything remotely referring to having a Solder Paste Deposition tester in house to check the printing process.
I have an interesting situation.
Any help would be appreciated.

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#19015

Solder Paste Inspection System. | 28 February, 2002

No, not as such. Nor should there be.

This is not to say that the issue of making good prints is anything but absolutely vital to cost effective operations. Experts attribute 60+% of SMT soldering defects to the printing process. Properly, both J0001 and A610 focus on the appearance of a correctly processed solder connection, rather than talking about tactics, techniques, and procedures or perhaps intermediate objectives.

And that makes sense. Why would a company that has invested in making a good print or doesn�t require sophisticated process want a bunch of old fuddy-duddies like the IPC decreeing that they spend all that money on a machine, training, NRE, and on-going process development that would add no value to their process? AOI machines do add value to processes, usually flow lines, where straightforward economics justify the purchase.

So, what is your "interesting situation"?

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Nightbull

#19017

Solder Paste Inspection System. | 28 February, 2002

Thank you for your reply.
Answer: Auditor came to my company and said that we needed a solder deposition tester. The reason was that we had no real way of assuring that our solder process was repeatable.
He referred to several IPC standards that made it seem we need to go out and buy a solder deposition tester.

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#19018

Solder Paste Inspection System. | 28 February, 2002

What kind of "auditor" is this?

Who does this auditor work for HP or CR Technologies? Maybe the auditor can quote 'chapter & verse' of the IPC specifications that state:
* Inspection of any type is required to assure solder print processing repeatability.
* AOI is required to assure that solder print processing repeatability.

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#19019

Solder Paste Inspection System. | 28 February, 2002

Hi Nightbull,
I'm with Dave. Don't see the need.
Good stencil, good operator, reasonable machine with at least manual vision alignment, good set up, solder paste that satisfies you and the customer, regular maintenance, and how can you go wrong?
Ask the "Auditor' to bring along their own inspection equipment, set up the printer, get it right until they are happy, store all the parameters and promise you'll always abide by those parameters. What can change? A lousy operator will cause hell, but that's about it.
If they want 100% inspection, will this increase your cycle times? - if so - requote and customer pays. If not 100% inspection - what's the point - see "lousy operator".
That's my two Bobs worth anyway.

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#19023

Solder Paste Inspection System. | 1 March, 2002

Hi Nightbull,

here�s daybull speaking.
Yes the same question for me, what kind of auditor was that ?
What I do in an similar audit situation is simply pointing to, if existing, an obvious lack of performance in certain processes depending on my humble understanding of what is adequate for that task the CM is supposed to do.
It�s not my function as an auditor to tell them how exactly they should do certain things, only advise that some performance may need some improvement.
If they ask me what I think can be done to solve certain problems I would give the advice I think of being the best for that particular situation.
AOI wasn�t the choice of the day yet.

Wolfgang

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CAL

#19025

Solder Paste Inspection System. | 1 March, 2002

I am on board with Dave F.(like I usually am). I can not imagine what IPC specs the auditor is speaking about. The Stencil Design criteria, 610, and 001 do not fit the type of solder deposition you speak of (nor I think they should). The machine parameters from Hand (manual) printing through full automation would be difficult to set into a standard. 610 and 001 were developed not to differentiate between machine types but acceptable solder joints.

I look at it this way....I travel from home to work. As long as I am there on time by boss does not care what kind of car I have or the gas that I put in. The auditor should not be over inspecting and worring about the amount of solder as long as the solder joints are acceptable.

I did have a revelation just now (incredible)...Have you recently introduced BGA's or currently useing BGA's???? Why do I ask??? Maybe the auditor can not adequatley inspect the solder joint under the BGA so he/she figures they can inspect post printing for good solder coverage. Just a thought.

Catch,
Cal

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#19028

Solder Paste Inspection System. | 1 March, 2002

Is your printing process is capable and in control?

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kg

#19079

Solder Paste Inspection System. | 6 March, 2002

How could you know if your printing process is capable or in control if you don't have a print measurement tool?

Still, I suspect it's a myth that 60% of SMT defects are screening defects. Are there data behind these figures or do we just continue attributing them to the great and powerful OZ - oops I mean experts ... (who dare to look behind the curtain?)

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#19080

Solder Paste Inspection System. | 6 March, 2002

Hmmmm, very good point.
I never thought about it much as such dedicated tools were not available when I first kicked off.
I'd look at the reflow under a microscope and if I could identify any problems, I'd start to look at the print using the same method. Not magi-lamps or Mantis/Vtek Spectras but a good binocular microscope with zoom.
Over a period of time I suppose you would say you develope a 'feel' for what is 'right' and what may cause problems, and where they're coming from - the problems that is - not the feels.
Is it the stencil?
Is it the paste?
Is it the printer set up?
Is it the printer?
Is it the pcb finish?
Is it the component?
Is it the placement?
Is it the oven/profile?
Is it the pcb.
Is it the dude who's running the whole sheebang?
Each of these questions on ther own have many different "sub-questions", if you like, that need scrutiny.
In the end the answer was usually "the dude who's running the whole sheebang" - me.
I hadn't done something as carefully as I should have.
I had lost my attention to detail for whatever reason.

Anyone who thinks you walk onto the floor and press the green button and away it all goes, is either the owner, or a fool.

You buy a machine because you believe in it's capabilities -WHEN IT IS PROPERLY SET UP!
When do you stop buying machinery/instruments to measure your machinery/instruments?

Is everyone still raving about nitrogen?
QFP's are old hat.
AOI will die in the arse.
As will BGA inspection/x-ray.

Because eventually you will get the process right.

How do we know it's right?
When our failure 'in case' rates drop to an acceptable level.
What's acceptable?
Up to you.
What caused the failure?
60% of the time the dude running the printer.

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#19086

Solder Paste Inspection System. | 6 March, 2002

> How could you know if your printing process is capable or in control if you don't have a print measurement tool?

You�re correct that you do need a measurement tool to determine if the process is capable or in control. A $1.5k microscope and some graph paper will do fine.

But the issue earlier in this thread was not the issue of whether measurements should be made or not. It was the accuracy of the references to requirement stated in IPC specifications made by the auditor. Demonstrating the process was capable and in control should be sufficient for the auditor to accept the process, rather the �smoke screen� of a requirement for a �solder paste deposition tester in house� thing that supposedly required in some non-existent IPC specification.


> Still, I suspect it's a myth that 60% of SMT defects are screening defects. Are there data behind these figures or do we just continue attributing them to the great and powerful OZ - oops I mean experts ... (who dare to look behind the curtain?)

Interesting observation. You�re correct. The same old chart seems to be endlessly repeated. There is probably no other story in SMT that is repeated so many times and for so many purposes as the �60% printing defects� story.

And this information could have been developed in a time when we were not as sophisticated about print as we are today. Yet the information keeps getting retold, like that boogie-man under the bed. [Although I happen to know that the boogie-man under the bed is true.]

In support of your point, I just when through several text and a pile of conference papers and found the boogie-man several times, but never found a reference. It was always:
* �It is well documented �
* �A number of studies �

On the other hand, it still wouldn�t surprise if that 60% number still held. We root back to the printer, paste, and the board effects on print much more often than P&P or the oven.

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kg

#19096

Solder Paste Inspection System. | 7 March, 2002

I can point to at least one recent study with contrary evidence that 60% of SMT problems are printing problems. The study is published in the APEX 2002 conference proceedings, a joint effort between Aglient and Nokia entitled 'Paste Inspection Study' (authored by Stig Orsejo from Agilent and Vishal Chatrath from Nokia). They found for the period under study that a shocking 0%!! of SMT defects were related to the amount of solder deposited. Obviously it won't be common that ZERO defects are caused by the screening step, but it does suggest we're mistaken to expect the ol' 60% figure.

In my own attempts to correlate solder joint defects to paste defects, I have found reasonably similar results. Most of the opens I see are not solder problems...many are lifted corner leads on gullwing parts. Many of the solder bridges I see do not correspond to paste deposits that were overvolume - certainly the paste was not bridging prior to reflow. I'll let you know when I publish the details ;}

It is rare to find a printing process that is truly in control (I'm not talking about paste height sampling to measure printing control folks...I'm talking 100% volume measurement and subgrouped Xbar and S charts). Despite the lack of control, I just don't think it drives a lot of quality problems. It may become tempting to tweak such a messy process though.

I am curious and intrigued about that microscope and graph paper though...what pray tell do you do with the graph paper?? Are you talking about measuring paste registration this way? Hmmm...ever done a GR&R on that method?

Thanks for the comments...

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JTorres

#19099

Solder Paste Inspection System. | 7 March, 2002

Dave, Yes the process is in control or that part that we can control. Visual inspection on first boards and then after a batch. I have had good prints with our current printing machines. My operators are very conscious of there work. Quality control on the other hand ensures that reflow is constant and within J Standards.

All in a nutshell.

Please note to all that contributed to the original e-mail, Thank you for the valuable information provided.

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#19109

Solder Paste Inspection System. | 9 March, 2002

Interesting findings.

I agree that probably no one does �100% volume measurement and subgrouped Xbar and S charts�. Who would want to spend the money? Isn�t the issue making things, rather than measuring things?

The microscope is used to make measurements. The graph paper is used to plot the results of the measurements.

We compared our method to a popular laser guided paste measurement tool that cost several tens of thousands of dollars. As I remember,
* Microscope [Smart Measure Optical Z-Axis measurement system] had a gauge between 10 and 15, probably around 12.
* Laser guided paste measurement thing had a gauge above 25, closer to 30 than 25.

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#19114

Solder Paste Inspection System. | 11 March, 2002

Don�t your recent findings on soldering defects point towards less need for AOI?
Besides that, I imagine that with 100% control and having only good prints being processed while the bad ones getting washed and reprint you will see this magical 0%.
Should be interesting what %tage was found not suitable for further processing.

Wolfgang

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#19116

Solder Paste Inspection System. | 11 March, 2002

#19117

Solder Paste Inspection System. | 11 March, 2002

I have read all of the previous threads and have found it very hard to believe what I am hearing.

The idea that AOI is not needed on your production line is like running a marathon without training before hand. You can only expect to get out of any given situations the amount from which you put in. Without some way of monitoring your process..How can you possibly expect to get high first pass yeilds? I guess we all need to jump on the ICT band wagon and spend all of our time simply doing electrical testing to verify our process. Oops..I forgot, the damage has already been done at this point.

If the printing process is not carefully monitored, you will "eventually" have issues within your process. If the placement process is not monitored, you "will" have issues with ICT. If you have issues at ICT, then you have bigger problems than you can imagine.

Also, the article referred to earlier stating "0" SMT defect created by the printing process must be a complete misunderstanding of the facts. Why would a company "Agilent" speak about a process tool in which they now offer and compete? Are they the "special" angels looking over the poor manufacturers without any regard for thier own future? I really don't think so. If you consider a previous article by Agilent called "One Billion Solder Joints and Counting..you will realize that the majority of defects found in this study could be in part attributed to the printing process. Maybe this is the reason they began offering paste inspection most recently?

Why do I feel so strongly about the need for post print inspection as well as all AOI as a whole? Well, I sell the equipment and know from the comprehensive studies conducted by the largest manufacturers worldwide that these tools provide a tremendous ROI. If these companies realize the benefits gained by AOI, then I would highly suggest others to listen to what they say. The day that an operator can repeatably measure solder paste or verify 100% component placement with a microscope, then the operator will obvously be something other than a human and I imagine most of us will be all living on another planet. It just can't happen! Well, maybe the planet thing makes sense with all of the problems happening around the world today. But, as far as a repeatable operator is concerned to monitor the process, Can you say subjective?

Now on the other hand, I also agree that you don't need to implement this level of inspction on your lines if you would rather spend the money on rework equipment and excessive scrap. But, does'nt it make sense that if you are already spending the money to repair defects, you may as well consider a method that SHOULD reduce these defects?

Unless someone can provide a true and proven study that idicates the opposite from what I offer, then the old idea that "you should not knock something if you have not tried it" fits very well within this discussion.

Keep the discussion moving. I would like to hear the success or failures from the use of AOI within the SMT production line.

Good day

Steve

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#19120

Solder Paste Inspection System. | 12 March, 2002

Steve,

>The idea that AOI is not needed on your production line is like running a marathon without training before hand.You can only expect to get out of any given situations the amount from which you put in.Without some way of monitoring your process..How can you possibly expect to get high first pass yeilds? <

Measure the time, average speed, heartbeat and , and, and, to see if you�re within the desired limits for your top performance. That�s what you need most whilst doing your training. During the actual race you need the figures that tell if your set limits are in danger or if you�re still in "time".
The issue seems to be what kind of equipment will serve you best, what measurement is to be taken to reach your selfset goal ?
Some say, a good runner knows how to run, when to eat, drink, speed up, save energy etc., he�s been training that over and over again. All he needs is his timer and some waymarks to judge his performance.
The more you want or the closer you try to get to the limit, the more you have to pay attention to those figures which you can�t control that easy. You have to invest and soon not only you are running the race, it�s more a complete team that performs the whole race. How big this whole enterprise is gonna be depends on ... hmmm, your goals ?, your performance ? your abilities to run at all ?

But during a marathon you can�t go back to start and do it all over again if something is not within a certain limit, ... you just fail !!!

So my advice still is, training, training, training ...
Good measurements tell me what to train most.

Wolfgang

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#19121

Solder Paste Inspection System. | 12 March, 2002

Wolfgang,

I agree with your training concept. The idea that you need to look very closely at what type of equipment to choose is also very important. The key point is not to eliminate any
of the options available based upon one view versus another.

My suggestion for any manufacturer considering AOI is to source equipment from the equipment manufacturer on a 30 day evaluation. This will allow each company the ability to decide for itself whether this type of equipment is a good "fit" for thier process needs. Most AOI companies at this time are looking for any opportunity to present itself.

Good Luck.

Steve

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BTaylor

#19122

Solder Paste Inspection System. | 12 March, 2002

I agree with davef on most subjects including this one , we have used a microscope and an experienced inspector for years and done just fine. Recently due to customer demands we an acquired an ASC 3-D inspection station, and it works great it told us our old process worked very well. It also helped with our stencil design. I think the new magic number is 80% of defects are caused by solder paste printing, I just got back from OZ.

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shan

#19158

Solder Paste Inspection System. | 15 March, 2002

80??? Whatever leads to you to that assumption?
I'd love to see a study stating that. Based on experimental results at our facility, overvolume due to the screener parameters have rarely caused a solder short. so, in conclusion, does one need a solder paste inspection system? Yes,
does one need multiple solder paste inspection systems to verify every board? No (only need it for intital setup verification and on an audit basis).

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