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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Solder paste height checking

JSS

#32750

Solder paste height checking | 18 February, 2005

Hi Everybody,

Mostly customer asked about the solder paste height checking after printing process.Is it compulsory to check the height if we are using stainless steel stencil and metal blades in fully automatic printer.Any technical answer to their question other than that we r using SS stencil and metal blades.Pros and cons of height checking and height not checking processes.

This message was posted Add this forum to your site! Click to learn more. the Electronics Forum @

reply »

#32752

Solder paste height checking | 19 February, 2005

Your customer asks a reasonable question. How do you know that your: * Paste has not dried? * Stencil aperatures have not become clogged? * On and on ...

Some agrue that printing is the most critical process and that it drives all down-stream failures. If that's the case, monitoring and controlling printing processes might be a good thing.

We've talked about monitoring paste height. Search the fine SMTnet Archives.

reply »

JSS

#32757

Solder paste height checking | 21 February, 2005

First of all THANKS for thr reply.

I totally agree with u that paste dried,stencil aperture clogged like probs comes during the production but we hv a visual inspection stage (with 5X illuminated lamp)after printing process and before inserting the brd in pick and place m/c.Such type of probs can be checked over inspection stage.But customer asked how are u checking the thickness of the solder paste. Don't u think that by incorporating the thickness check in the system in every card can lead to our production loss due to more stops? Thickness check of solder paste is actually reqd or not if we r using metal squeegee blades?

Thanks.

This message was posted Add this forum to your site! Click to learn more. the Electronics Forum @

reply »

#32759

Solder paste height checking | 21 February, 2005

Solder paste thickness control is more important in SMT process. What controls do you have? I guess if everyone follows the critical control path, then there are always reduced problems. The issue is no one is perfect. Paste tends to be on the stencil for many reasons such as machine breakdowns, component issues oven issues and so on. Once the line stops, then the paste dispensed already on boards gets the beat first. Bulk paste on the stencil may not have much impact, provided the line stops for more than 3 hours.

What sort of a problem do you have? single pin failures or multipin failures? Paste height is as much important as component co-planarity. If a particular pin does not touch the solder paste during re-flow, (either of the reasons), the resultant will be a sure non-wet. We can discuss more, looking at your problems. Regards, GV

reply »

#32761

Solder paste height checking | 21 February, 2005

Paste height may not be an accurate measurement always. May be a good practice is to measure the weight of the board after solder paste printing. 30 samples is a good number. Have a Cpk > 1.67 always on the sample boards measured. This is very fast and pretty good measurement for a paste dispense control. Boards do not stand out-side for long times. Inspect the height for critical components only, in the initial stages. Once your Cpk is stable, you can do away with the height measurements. I have also seen good control of paste height with electro formed metal stencils. The aperture has a stable and uniform size. Regards. GV

reply »

JSS

#32798

Solder paste height checking | 22 February, 2005

We r using QFPs of 0.5mm pitch and r not getting any soldering prob at the end.But some new customer insists upon the thickness check of the solder paste after printing.

At present we don't hv thickness checking system.We r controlling the amount of solder paste by using "Laser cut Stainless Steal stencil","Metal squeegee blades",Fully automatic MPM paste printer in which we can control "Printing speed","Snap off","Squeegee pressure","PCB releasing speed after printing"etc with the help of software. So needs your views that thickness checking system is actually required or not.

Thanks for the reply.

With best regards

JSS

This message was posted Add this forum to your site! Click to learn more. the Electronics Forum @

reply »

#32802

Solder paste height checking | 22 February, 2005

We hear you. If it's not broken, why fix it? Right? Well intentioned, but not very educated customers seems to be part of the bane of existance of process engineers at contractors.

First, as a previous poster said, paste height is an improper measure of proper printing. Paste volume is a more accurate measure.

Second, you can get away with measuring height fairly inexpensively and not affecting process flow much from what you're doing now. You could replace your inspection loop with a height measuring microscope. It'll cost you about $1k. Search the fine SMTnet Archives for the names of suppliers. Use "microscope and paste".

reply »

JB

#32804

Solder paste height checking | 22 February, 2005

A couple of features on your stencil printer that should help with a couple of potential printing processes:

A temperature control unit and the automatic understencil cleaning with the chemical of your choice. That alone, will reduce the chances of having the fluxes drying from your paste and keeping your stencil apertures clean.

reply »

#32907

Solder paste height checking | 27 February, 2005

Hello my name is Jason. And I to work in electronics. I have recently had the same inquires by costumers about solder height to. Are these well-known customers like hp or micron? Cause it sounds like it to me. Who do you deal with that makes these inquire? I'm hoping it�s only in certion areas of electronics. Because I would hate to loss a customer do to the fact that I don't measure my solder height also. If you could help me I would very grateful thank you.

reply »

ABHI

#32987

Solder paste height checking | 2 March, 2005

Guys, Solder paste height worries all of us as we encounter the non wets after reflow. More so in fine pitch QFP's. The non wets are not always caused by solder paste height. Many other contributors. Even the pad geometry on te board can contribute to the non wets. We have seen it all. Coplanarity / pad geometry / package warpage / paste volume / nature of IO (ground pin, power pin)/ reflow profile (soak time, dwell time)/ solder paste condition / stencil aperture clogging, cleaning and so on. Insist to your customers that you need to look into his process and my experience is the problems can be solved only, if supplier / customer works as partners. Both parties have to be very open to solve the issues.

reply »

#33444

Solder paste height checking | 30 March, 2005

All,

Has there been any finding from the component point of view in terms of non wets after reflow and if yes, can anyone share what was improved on the component to reduce the non wet defective levels. What would be the contribution from the component side to non wet defects as compared to the SMT process itself? I am more interested in fine pitch QFPs performance. Thanking everyone in advance.

reply »

#33445

Solder paste height checking | 30 March, 2005

Considerations are: * If the nonwetting is component lot specific, the could be solderability issues with that lot. * If the nonwetting is is a broader based component issue, the solderability protection on the component may require a different reflow recipe.

What is the nonwet situation? How broad is the problem? More detail would be helpful.

reply »


URL

#33454

Solder paste height checking | 30 March, 2005

This is a pet peeve of mine. The paste height requirement is generally asked because the customer has no clue about screen printing, but knows to ask this question. If he did know even a little about printing, he�d ask you to assure the �volume� of solder paste. Think about it. Generally, when you do paste height measurement, it�s with a laser. That small part under the laser might be OK, but half the pad could be missing and you�d never know. This would result in a poor solder joint. It�s the volume of paste that reflows to a liquid that assures your solder joint, not the height. That being said � you state you have an MPM printer. You may already have the 2D camera option? If so, this is a great start to assure the paste is where you want it, but only from a 2D standpoint. They make a 3D laser that can be put in the machine and works rather well. You can even collect the SPC data and down load it to your customer (o-la-la!). JB mentions something about the environment controller MPM offers, but it blow so much air around it�ll dry out your paste in no time � I wouldn�t buy it.

So challenge your customer and show him you know your business. Educate him a bit and I think he�ll have a bit more respect for you.

reply »


ams

#33467

Solder paste height checking | 31 March, 2005

Yes, components do contribute to the non wets in fine pitch reflow. Oxidation is the main culprit. May ask where it is coming from. Can not say in particular. May be burn in test process or end of line baking, hot / cold testing and need to run DOE's to find the area of oxidation. Also agree that it is purely lot depends on lot to lot. Many lots will be very clean and there goes a lot with non wets with quite a bit of PPM.I have had some experience with such lots. Couple of lots had non wet failures at a peak T of 210C-215C. When we raised the peak to 225C - 230C. The lot went through with out any failures. Watch out you may have other problems like capacitor tombstone effect due to higher temperatures. All parameters on the printing are the same. just the temperature was increased and the same lots had reported no non wets. The amount of oxide on some bad leads does get repaired at higher temperatures.

reply »

cn

#33469

Solder paste height checking | 31 March, 2005

I agree with chuck, but would like to add. 2D is a great option and helps to keep your printing process in check, it will measure the x & y coverage on the pad. It will help you determin when your stencil aps become clogged or when the bottom of your stencil needs to be cleaned.... It will also help you catch solder shorts should you get them after print. BUT, it will not tell you if the solder paste height is out of spec or irregular. We implimented paste height inspection years ago when we were using manual screen printers because of variation in the setup. We found that if operators setup the printer incorrectly we would end up with solder shorts or iregular solder deposits. If the print speed or suport or separation speed..... was incorrect the deposite was not uniform or complete. If you buy the proper paste height equipment it will measure the entire pad vs 1or2 spots on a pad. With our system it gives you the average hieght. We do not have this in line, its an off line system and we use it to check setup and if its a high volume job hte operators have to check it throghout the run. So I think your customers are correct to ask if you are at least checking it.

reply »

SMT in-printer dispensing

ii-feed SMD Intelligent Feeder