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OSP / Paste Printing Problems

OSP / Paste Printing Problems

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We are producing quite a lot PCB:s with Organic solderabil... - Aug 28, 2002 by

What kind of print problems are you Having? Off pad, Voids? ... - Aug 28, 2002 by Lysik

Problem description: pads of PCB:s seems to "reject" solderp... - Aug 29, 2002 by

You have may have already checked this but verify stencil de... - Aug 29, 2002 by Lysik

That you are getting BIG gobs of solder on the pads indicate... - Aug 29, 2002 by davef

Dave, you did not understand my problem right. We don�t ge... - Aug 30, 2002 by

Oooo, I get it. Sorry I am so dense. So, as Johnny Cochran... - Aug 30, 2002 by davef

265 is a great unit. Your process should be OK. I am sorry I... - Aug 30, 2002 by Lysik

Thanks Guys, I agree, you have to start with basics. Tr... - Sep 03, 2002 by

Sorry so late in getting into this tehcnical issue. I have s... - Sep 12, 2002 by scottefiske

TLe

#21340

OSP / Paste Printing Problems | 28 August, 2002

We are producing quite a lot PCB:s with Organic solderability protection on them. With some products we have printing problems eventhough printing parameters and PCB manufacturers for boards are same. Question: Could it be that the OSP itself or some rejective material from PCB manufacturing process is behind this kind of problem?

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Lysik

#21345

OSP / Paste Printing Problems | 28 August, 2002

What kind of print problems are you Having? Off pad, Voids? Or is it slumping, etc? You really should be all set with OSP boards. If I can get some more specific info I could probably help.

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TLe

#21355

OSP / Paste Printing Problems | 29 August, 2002

Problem description: pads of PCB:s seems to "reject" solderpaste. Problem is more easy to identify on larger pads where the paste forms a double layer of paste on the other end of the pad and on the other end there is no paste at all. On smaller pads, on same boards where we have problems also with bigger pads, there is no paste at all on some areas of the PCB.

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Lysik

#21357

OSP / Paste Printing Problems | 29 August, 2002

You have may have already checked this but verify stencil design (aspect ratio) and make sure you are using the correct paste (mesh size) Also look at perint pressure. up to 2 lbs per inch of blade used. You may also want to use a slow break away when printing is complete. What type of printer do you have? does it have a under stencil cleaner?

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davef

#21368

OSP / Paste Printing Problems | 29 August, 2002

That you are getting BIG gobs of solder on the pads indicates that your print / paste process is probably OK. Sounds like someone did something bad to the OSP. Tell us about: * Supplier and brand of OSP that your board fabricator used. * Number of thermal cycles that these boards see. * Type and number of clean / wash cycles that these boards see. * Age of the boards. * Conditions and packaging during storage.

Were these boards solderable when you received them from your supplier?

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TLe

#21370

OSP / Paste Printing Problems | 30 August, 2002

Dave, you did not understand my problem right. We don�t get paste on the PCB in the printing phase of process. I have seen also poor wetting on OSP, as you descriped, but that is very unusual. I think generally OSP is better than gold/nickel if speak about wetting and joint reliability. Anyway, the manufacturer is WUS Printed Circuit (Taiwan), the boards see one or two reflow cycles (depending on product), we are not allowed to wash these PCB:s, they are packed in vacuum and the age is less than 6 months. Tri Jet, stencil design is OK (at smt area I�m very careful of saying something is absolutely OK). As a printer we have DEK 265 infinity and as you know it should be one of the best printers that you can have.

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davef

#21381

OSP / Paste Printing Problems | 30 August, 2002

Oooo, I get it. Sorry I am so dense. So, as Johnny Cochran might say, your pads are so slick that the paste won�t stick. So, either: * Someone is slimming your boards with goop that prevents the paste from sticking on the pads. Some plastic bag have a mold release that can get on board. It this stiff silicone? Is it just on the pads or on the whole board? * Your paste has lost tack. [I assume you'd catch this one real fast.]

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Lysik

#21388

OSP / Paste Printing Problems | 30 August, 2002

265 is a great unit. Your process should be OK. I am sorry I asked you to check it I just wanted to start with the basics. I am at a loss. May be a bad batch of paste. I am reaching for straws. I know it sounds crazy but try a really slow (snap off) with a large snap off distance. Sounds really simple but printing can sometimes be like wave soldering an art not a science. What ever works is OK. then find the root cause. I hope you are not offended by my simple response

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TLe

#21393

OSP / Paste Printing Problems | 3 September, 2002

Thanks Guys,

I agree, you have to start with basics. Tri Jet, you have a point there: " art not not a science". Basically, it is a simple process. Maby that is why we "rocket scientists" try to get far-fetched answers to our process challenges, it is too simple for us. Anyway, the most potential reason would be the paste. I will check that "mold release from package" thing. I also have to get some boards investigated.

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scottefiske

#21515

OSP / Paste Printing Problems | 12 September, 2002

Sorry so late in getting into this tehcnical issue. I have seen this condition before...90% of the time in conditions of adhesion on a water soluble material... is the paste...exposure time, lot issue, etc..basically the paste's carriers and binders have fallen out of spec. causing non-wetting and adhesion problems..clogging apertures etc. Any additional questions please feel free to contact me at scottefiske@hotmail.com. Scott

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