Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Screen Printer Visual Inspection Equipment



Screen Printer Visual Inspection Equipment | 16 December, 1999

Hey Folks:

I just want to get an idea how many of you use in-line or off-line visual inspection for solder paste deposition? At my company, we have one off-line, and it inspects for paste height. It's not always consistent either. Sometimes, it gives a "low" or "high" reading and when you visually inspect the board, it and the solder joints look just fine. PLUS, we already do 2-d inspection at our screen printers....

How many of you find this type of equipment useful? Has anyone benefitted from incorporating this type of inspection in their process (i.e. has anyone been able to make process adjustments to their printers because of the data that this eqpt. provides)?

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Karl M


Re: Screen Printer Visual Inspection Equipment | 16 December, 1999

I would like to talk to you about contact at check out

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Re: Screen Printer Visual Inspection Equipment | 16 December, 1999

Hey C.K, If you are looking for inspection of the solder paste before reflow, there are many types of inspection: 1.Paste height measurements at random positions 2.3D inspection with shadow contrast capabilities based on an autocad format 3.3D inspection using laser variables for changes in pad and masking heights. If you are looking for solder joint inspection after reflow: 1.X-ray machinery w/programmable location scan 2.3D inspection with shadow contrasting based on an autocad format

Some screen printing equipment have options for upgradable hardware and sofware that can improve the machines inspection limits.

As far as choosing deciding on new equipment, go with what best suits your needs...cost, time, reliability.

I hope this helps.

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Alex B


Re: Screen Printer Visual Inspection Equipment | 17 December, 1999

Hi, C.K. Let's assume that your stencil's thickness is in a range 4-6 mil or by other words the height of the solder paste on a pads is the same (close enough to reality) Therefore, for pad's width more than 20 mils(as well as pitch between pads) the hight of solder paste can be neglectable (because 4-5 times less)in comparision with pad's width and no reasons to introduce any kinds of 3D-inspection. Your solder joints would be 100% OK with all yours "hills" and "wells" and 2D-printer's vision will keep this job perfectly well. You can easy forget off-line solder inspection or by chance to sell this expensive staff to your concurrents. But, if you are working with ultra fine pitches (10-12 mils or less))it will be another situation and 3D can help. 12-15 mils range is still good for Printer's 2D inspection and 3D-staff will be your choise (by my opinion it isn't necessary yet)

Cheers, Alex

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Brian W.


Re: Screen Printer Visual Inspection Equipment | 17 December, 1999

I used an off-line paste height measurement device to control my paste process. I did not inspect every board, just a random sample once an hour. I have used both manual and automatic devices. I like the automatic becuase: 1 - I have no "operator" variation. 2 - I get more average sample readings than just 5 pads per board. 3 - I get the increased readings in less time.

I let the automatic 2D systems on the screen printers monitor the process in between sample readings.

The paste process is THE most important part of your SMT process. The paste process can be subject to many different factors. Temperature, humidity, time on screen, and many other factors interact to constantly affect the paste. What works this morning may not be working this afternoon. Plain visual inspection is not enough to control the process. The paste process can be at the root of so many types of defects. Control chart it, monitor, control it, and your SMT process will go MUCH better. If you don't control it, you will always have variations in your process. How good do you want the process to be. At one company, we had it under 50ppm, and that includes doing 20 mil or less fine pitch. Much of that is the result of monitoring the paste process, and carefully planning all the steps in the process and reducing their variation.

Brian W.

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