Solder paste SPC analysis

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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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.

Philip

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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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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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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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