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Solder paste SPC analysis



Solder paste SPC analysis | 25 October, 2000

A question mainly for Dave. F, but if anyone else can help I would be very grateful.

We (as a, process engineering dept) are getting crucified by our �internal customers�. ��The QUALITY??? Dept�� regarding information taken from solder paste height measurements. I have my own feelings about these measurements, but shall refrain from making them public. The quality dept are taking things very seriously and are performing SPC analysis on the raw data and coming up with all sorts of predictions.

Do you think these measurements are required?. What are other people doing to monitor solder paste deposition. Am I being too critical on the quality dept or do they have the wrong end of the stick, as I think!.



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Re: Solder paste SPC analysis | 25 October, 2000

Paddesign, aperture size and stencil thickness determine the amount of solder for your joint. Once you have found suitable parameters you need to control the volume of your paste deposit which is influenced by printer settings, paste condition, stencil cleanliness and environmental influence. So you know what volume range will be suitable for good results and one means of determining the volume is the height measurement. Taking regular height measurements will show if something is going in the wrong direction and enables you to adjust your settings. Taking these readings, recording them for each batch enables you in combination with other processcontrol figures to find a cause for defects more easily that will show only at a later stage and helps you to prevent "coffee ground-readings". (I would like to have such figures in case of troubleshooting a line.)

Besides, it�s necessary to have some attentive operators performing the inspection, they can see more at a glance and can perform immidiate corrective actions. It�s also absolutely necessary to have procedures for recycling missprinted PCBs. If not, all your measurements don�t mean a thing. And if you have those figures isn�t it nice to have them at hand if a customer has some sort of reclamation suspecting something went wrong with your processes ?

M2C Wolfgang

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Philip A. Reyes


Re: Solder paste SPC analysis | 25 October, 2000

Hi there!!

You know what your QA is doing is right, coz by measuring the solder paste height can avoid the following defects: 1.Insufficient solder 2.Short solder or bridging 3.Solder balls

SPC monitoring for paste height checking is required in Screen Print Process. This will help you a lot in controlling the process, coz some of post-reflow defects comes from paste printing. FYI. Other alternative for measuring paste deposition, you can use the scope with x and Y measurement the Z-checker for the height and then you can compute the volume.


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Re: Solder paste SPC analysis | 25 October, 2000

George: Crucifixions!!! YES!!! I love crucifixions!!!! [Well I do, providing I�m not the crucifixee that is ] The pomp, ceremony, wailing, grumbling, and brat on the grill.

You�ll find little sympathy here. Phil and Wolfgang make good points. Consider: * 60 percent of SMT soldering problems track back to the printing process. * In qualityland parlance soldering is a "special process" [The results of special processes cannot be verified fully by subsequent nondestructive inspections.] * It�s tough inspect soldering. So, good process control is critical.

Help us understand the issue better. You have made well thought-out contributions to the Forum and it doesn�t seem like you to be hesitant to support steps toward greater process understanding and management.

Are we talking style???

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Re: Solder paste SPC analysis | 26 October, 2000


where exactly is the diagreement ?, is it on the point if you should be doing the SPC on the paste or is it how the data is being interpreted ?

The problem with SPC is every quality bod has another idea as to how it should be looked at, Xbar, cusum range...the list is there some where in the archives no doubt.

What Dave, wolfgang and phil are saying is true you do need to do it, and not just for those pesky internal custmers but also those lovely wonderful external ones as well and not forgetting the various quality bodies (ISO / ANSI etc..) within the plant I work in we're no wgoing one step further and working on SPC limit's for GLUE!!!!! that's gonna be fun right?...Dave...Dave...are you there??...what do ya think about that one!...

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Mika Pirttimaa


Re: Solder paste SPC analysis | 26 October, 2000

Well, Yes those measurements are required as long as your process is not in control. It is true that quality people easily demand too much and are too strickt in the areas that are not so important. Height of the pad is one of them, it is not very informative thing to measure, although, it should be on reasonable area. For the quality of the pasteprint-process are better indicators like the area of printed paste.

High pasteprint quality is possible to reach but you have to have all subprocesses in contron before it is realistic. It starts from stensil design and ends to printing parameters.

WBR, Mika Pirttimaa

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Re: Solder paste SPC analysis | 26 October, 2000

I'd like to respond here not just to throw in my $.01 (I yield at least a penny to the more knowledgeable contributors), but to verify that my thoughts on this are reasonable...

How about, you either do in-process inspection or testing, or you validate your process by verifying (through experimentation)that if you control a set of variables properly, you get repeatable and acceptable results? You gotta do this on print area too, or you're just painting half the picture.

Tell your quality department that you'll be happy to execute the validation protocol if they'll write it for you. They'll love that.

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Re: Solder paste SPC analysis | 26 October, 2000

John: I�m here.

On "what do ya think about that one!..."??? Mutha, that sounds rat�s rump [as Dennis Miller says] ugly.

On some boards, we paste a cuppla chips on the break-away panels and then torque the chips from the board after cure. We use the "Jimmy �THE Rocket� Johnson Torque Test". His test, Jimmy uses a pair of duckbill pliers and hymms in approval when he torques the chip and it snaps-off "properly."

If push cames to shove, I guess we could have Jimmy do his test with a quantifiable method, document it, chart it, bla bla bla. But we started doing this test when we thought the wave was ripping glued chips from the bottom of boards, chewing them up, and barfing them up as dross. [We�ve talked in the archives about the stupidity that concept. Right, kids???]

I guess the issue becomes � sawatza property of glue cure are you looking to control? Assuming we�re talking second side SMT component adhesive, if it�s: * Cure strength: It�s silly to do a bunch of charting, because the cost of rework alone should be enough of an incentive to get a good cure. There�s other reason�s, but I can�t think of them rite now. * Complete cure [because poorly cured adhesive can cause LT reliability problems, beyond the issue of getting a good wave solder flow]: This could be worth charting, but it�ll be a tough measure, because the outside of the glue cures before the inside. So, I guess you�d be sectioning the glue and testing it for cure, hummm delectable!!! * Ionic residue developed during cure: Boards should be analyzed for ires, regardless of source.

Good luck, Bud. Please come back some time and tell us stories.

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Re: Solder paste SPC analysis | 26 October, 2000

Steve: You make sense, but I don�t see where someone that's getting fitted for a cross is in much of a bargaining position.

Oh, and you MUST charge full market 2� rates for your thoughts. We�ll have no submarket price offerings. Although, the Fair Pricing Standards Board is still discussing what to do about those "pence" jamokies.

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Re: Solder paste SPC analysis | 27 October, 2000


you know the problems about working for a CEM all tose wonderful customers and managers love their graphs! Got 1 eng manager that is pushing everything to double sided reflow (even if the card ain't designed for it!) as he's insisting glue ain't a robust process....and what's his bais...cos we don't have any data to the contary! Been working with a vision master for checkingpaste heights, turn's out the little sucker work's great on glue as well, I got some pic's if you wanna see them....


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Re: Solder paste SPC analysis | 27 October, 2000


Ooooo, leave it to me to miss THOSE customers!!! Darn, as you can see from my response, I was thinking ... well let's just leave it at that.

YESSS, let's use as much capacity of the heavily loaded part of the shop and not use available capacity in other parts of the shop, even when it produces equal quality. Hmmmm

Wussa "vision master"?

Pix!!!! Neat!!! "Holiday pictures??? Wink, wink, nod." Could you post the pix on i-drive ( or Driveway ( [I've already arranged for you to get a 20M virtual hard drive there. Watta guy!!!]

Ima packing my gear and going golfing. Have a nice weekend yins.


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