Hi there, kindly help to advice me either epoxy/glue at bottom SMT component such as chip package 2012 will cause the component to be non-wetting after run reflow process?

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davef

#52627

Epoxy on bottom of SMT component | 23 November, 2007

We're not real clear about what you're trying to discuss, because most capacitors are packaged in epoxy with a solderable termination on each end. But lets throw a couple of ideas at the wall and see what sticks. If this epoxy is: * From the capacitor fabrication process, where the packaging material has encroached onto the solderable termination, soldering the portion of the termination that is covered with the epoxy could be difficult. * Chipbonder used in the circuit board assembly process, where the chipbonder used to hold the component in-place during wave soldering that side has spread onto the solderable termination, soldering the portion of the termination that is covered with the epoxy could be difficult.

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shy

#52635

Epoxy on bottom of SMT component | 25 November, 2007

Hi Devaf, Sorry to make unclear statement earlier. I believe the issue that i'm trying to discuss is regarding the adhesive that place beneath (center) the component to prevent it from drop during wave soldering process.

Normally the component package that being glued is 2012/0805 and above.

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davef

#52639

Epoxy on bottom of SMT component | 26 November, 2007

Sure, if you slopper or schmush chipbonder onto pads, solder will not take on that portion of the pad, regardless of the component.

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Real Chunks

#52644

Epoxy on bottom of SMT component | 26 November, 2007

Even a slight amount of epoxy will prevent a part from soldering. Look at the part after print. If you any trace of you epoxy between the pad and part, you have a potential problem.

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shy

#52654

Epoxy on bottom of SMT component | 26 November, 2007

Hi Real Chunks, kindly help to elaborate more on the potential problem that i will face?

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shy

#52655

Epoxy on bottom of SMT component | 26 November, 2007

Yes, i'm agree with you davef but i'm not put the chipbonders onto pads. i'm put the chipbonders at the beneath component (center between both component terminals) which the idea is to hold the component during wave soldering which might cause the component to de drop/missing.

Is this chipbonders will cause any effect at the component terminal since it will cause the component slightly higher than the pad and solder paste?

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davef

#52657

Epoxy on bottom of SMT component | 26 November, 2007

Shy: Oh, we NOW understand what you're asking. Sorry to be so dense.

We agree that the standoff of component from the board could end-up being a little heigher than the pad height when using chipbonder adhesive. We rarely see a problem.

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shy

#52658

Epoxy on bottom of SMT component | 26 November, 2007

currently i'm open my stencil aperture is 80% from the land pattern. is this will cause insufficient solder at the terminal component or not? the stencil thichness is 6mil and the board run using SMT pallet which i consider there will be no option for warpage.

since you're rarely see this problem, you might help to give idea how to eliminated this kind of issue which causing my SMT component to be non-wetting after reflow.

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Loco

#52659

Epoxy on bottom of SMT component | 27 November, 2007

you say you use the glue to keep the components on during wave, why would you want to solder them twice, once in reflow and once in wave?

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shy

#52660

Epoxy on bottom of SMT component | 27 November, 2007

Hi Loco, my PCBA got top side and bottom side and 90% SMT and 10% THP (top side) which need to be cover by wave solder. And that's why i need to go through reflow and wave.

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Real Chunks

#52661

Epoxy on bottom of SMT component | 27 November, 2007

I'm still confused. Why reflow solder a part when you're going to wave solder it? Seems like a waste of resources and material.

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shy

#52662

Epoxy on bottom of SMT component | 27 November, 2007

solder the part is for SMT component (located at top side and bottom side) and wave solder is for THP (located at top side only).

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davef

#52663

Epoxy on bottom of SMT component | 27 November, 2007

We do not paste when we glue. We glue components so they will stay inplace during wave soldering. In wave soldering there is ample solder to bridge the standoff between the component and the pad.

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shy

#52664

Epoxy on bottom of SMT component | 27 November, 2007

is there any gap between the pad and terminal if we place the glue? Btw, my practice to print solder pate then punch glue then PNP component and finally reflow. Also we find drop/missing chip after wave eventhough we glue the component.

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davef

#52665

Epoxy on bottom of SMT component | 27 November, 2007

C1: is there any gap between the pad and terminal if we place the glue? R1: Yes, there is a gap, but it is easily bridged by the amount of solder in the wave.

C2: Btw, my practice to print solder pate then punch glue then PNP component and finally reflow. R2; Our practice is to print glue, place, cure, then wave solder

C3: Also we find drop/missing chip after wave eventhough we glue the component. R3: There are times when components are not in-place after wave soldering. Odds are: * If the component was in-place prior to wave soldering, there is a problem with glue cure or age of the glue. * Most likely, the component was not in-place prior to wave soldering and was damaged during handling. * We have talked about this previously. Search the fine SMTnet Archives for more.

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shy

#52666

Epoxy on bottom of SMT component | 27 November, 2007

How many mils the gap between the terminal and pad?

Your practice is for technology SMT-4?

What is problem with glue cure? is it due to the reflow profile? how long the glue can be keep in room temperature with humidity 40-60?

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Dback

#52669

Epoxy on bottom of SMT component | 27 November, 2007

Shy,

What is your current method of applying adhesive? If the terminals of the component that has adhesive are not wetting ( or not forming a solder joint I think we are talking about ) after reflow, then you must be applying too much adhesive.

As a rule of thumb, if I am not mistaken, the adhesive height should be that of the distance between the bottom of the component and the surface of the PCB.

The adhesive cures faster than the solder paste, so once the adhesive sets, the component terminal may be "floating" above the solder, causing the terminal not to wet.

Can you control your adhesive height? Start be looking at it and post your observations.

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shy

#52674

Epoxy on bottom of SMT component | 27 November, 2007

Dback, Current method is by using dispenser machine to dispense the glue at PCB. This non-wetting is randomly and not repeating to the same location.

My adhesive height is 0.01" to 0.035". Is this will cause the component to had a gap between the terminal and pad?

Yes, i agree with you that the glue will be cured first and hold the component. Btw, is this any related with stencil opening since my current opening for chip component is dog bone whith thickness 6mils and i believe this cause the non-wetting issue.

The adhesive height being control by using the measurement tools which called glue gauge. Every panel being control the height and follow the value which in our standard procedure.

I've already done some evaluation to reduce the heigh of the glue but it fails at wave solder which cause the component to be drop/missing.

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davef

#52675

Epoxy on bottom of SMT component | 27 November, 2007

Q1: How many mils the gap between the terminal and pad? A1: It depends on properties of the glue and z-force when the component is placed by the assembler.

Q2: Your practice is for technology SMT-4? A2: We don't understand SMT4. We know that very smart people characterize the levels of assembly complexity with various code words. We don't pay attention to those machinations, because that kind of stuff seems to make money for the smart people only and none for us.

Q3: What is problem with glue cure? is it due to the reflow profile? A3: Glue suppliers recommend a thermal recipe to cure their particular product. Some assemblers choose to ignore those recommendations and use a reflow thermal recipe, even though their supplier recommends a different recipe. On the other hand, some glue formulations can be cured with a reflow thermal recipe. If you don't follow your supplier's recommendations, and you don't know better, it might not go well for you.

Q4: how long the glue can be keep in room temperature with humidity 40-60? A4: Until you know better, you should only keep glue at "room temperature with humidity 40-60" as long as your glue supplier recommends.

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davef

#52676

Epoxy on bottom of SMT component | 27 November, 2007

Shy: You say, "I've already done some evaluation to reduce the heigh of the glue but it fails at wave solder which cause the component to be drop/missing."

Based on your evaluation, questions are: * What is the relation between component standoff and drop missing? * Do all components with the same standoff have the same / similar drop / missing rates? * Are you positive the components are present when loaded onto the wave solder machine?

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shy

#52678

Epoxy on bottom of SMT component | 28 November, 2007

is there any standard gap between the terminal and pad if we place the glue?

SMT-4 mention as per what you understand which is using glue at SMT without solder paste and run at wave solder for the solder paste at the terminal.

Glue supplier recommended to cure at 150C but if combine with solder paste specs it will be fail. is there any idea to combine reflow profile for solder paste & glue?

supplier provide the data but sometimes, the output is not as per what thoery said and will had some drop issue after wave.

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shy

#52679

Epoxy on bottom of SMT component | 28 November, 2007

Q1:What is the relation between component standoff and drop missing? A1:component standoff will identify either solder paste at SMT side can form the fillet at component terminal or not. Drop/missing component is totally out of the topics since i just need to know if there is any gap between the component terminal if we mount the glue beneath the component. Plus, is there any issue if we using glue and masking 100% for bottom component before run through wvae sodlering?

Q2:Do all components with the same standoff have the same / similar drop / missing rates? A2: not all but randomly.

Q3: Are you positive the components are present when loaded onto the wave solder machine? A3: affirmative.

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davef

#52681

Epoxy on bottom of SMT component | 28 November, 2007

So, you're curing glue on a thermal recipe intended for reflow even though your supplier recommends that you cure at 150C, because you want to use paste that isn't necessary.

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shy

#52682

Epoxy on bottom of SMT component | 28 November, 2007

the paste is necessary for the component that had no glue. btw, for solder paste specs, 150C is at reflow time plus soaking time and i believe it will cause nothing to the glue and can cured as per recommended? correct me if i'm wrong.

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Real Chunks

#52695

Epoxy on bottom of SMT component | 29 November, 2007

Dave,

Eject-eject-eject!

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Steve Thomas

#52696

Epoxy on bottom of SMT component | 29 November, 2007

Ahhh, our first casualty.

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Stephen

#52697

Epoxy on bottom of SMT component | 29 November, 2007

I really hate to ask but must. Are the components that are falling off, the components that don't have glue? Seriously not all the parts on the bottom are glued on? How do they stay on during the wave?

The normal way is to run the top SMT as normal, and relow them, then stencil the bottom side with epoxy (all the SMT parts)populate the parts then cure it. Then populate the PTH parts then wave it.

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Real Chunks

#52698

Epoxy on bottom of SMT component | 29 November, 2007

Nope, my thought process ejected from my brain and will have to watch this thread pan out from the side lines. Should be interesting.

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Steve Thomas

#52699

Epoxy on bottom of SMT component | 29 November, 2007

It's OK, really. Stephen is carrying the torch for you now, although I don't know if dave is in or out at this juncture.

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Real Chunks

#52700

Epoxy on bottom of SMT component | 29 November, 2007

Shouldn't someone LIGHT the torch first?

Good ol' Adolph starting a tradition that carries into today.

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Dback

#52701

Epoxy on bottom of SMT component | 29 November, 2007

Shy,

You mentioned that you are using "dog bone" apertures for your chip components? It doesn't make sense to me. I thought that the "dog bone" was used for fine pitch devices, to keep the solder away from the center and avoid bridging.

It doesn't make sense.

Maybe you just don't have enough solder on your pads.

We have a similar process, screen paste, dispense adhesive, PNP, reflow. And all of our parts are soldered and have pretty solder joints.

We use home base apertures and 5 mil stencils.And SMT adhesive.

If you ever solve this problem, please post your solution, something just doesn't add up.

* throws towel in*

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davef

#52704

Epoxy on bottom of SMT component | 29 November, 2007

Dave OUT!

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shy

#52709

Epoxy on bottom of SMT component | 29 November, 2007

Hi Stephen, The component falling off is the component that had glue. the component witout glue is being covered by masking during wave.

What is the meaning by populated the part and cure it? is it run with solder paste profile or glue profile or you combine both? What normal practice for me is running Bot & dispense Glue then reflow both (glue & solder paste), then run top side. after finish SMT we run THP and then run wave.

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shy

#52710

Epoxy on bottom of SMT component | 29 November, 2007

Hi Dback, Yes, i'm open "dog bone" aperture for my chip component. this is to prevent solder ball issue. For fine pitch i'm opening square with full length and half width to prevent bridging. Btw, if "dog bone" is not for chip component, what is your opening for chip component?

You using 5mil stencil with home based aperture opening. Doyou have 6mil stencil? What is the opening?

I'm not be able to solve the problem due to the gap between the pad and the terminal which causing non-wetting to my chip component. If the solder paste is not enough, you might be able to advice what is the solderpaste volume needed for chip component?

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Stephen

#52714

Epoxy on bottom of SMT component | 30 November, 2007

We put glue on the bottom of the board that already has the topside SMT mounted. We populate the board. We put it through a cure profile.

At this stage the topside components are soldered on. The bottom side components are glued on with NO solder on the joints.

Why would you want solder on them at this stage? (this is what the rest of us are wondering.)

When then put the boards through the wave solder machine. After this all components are now soldered.

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Dback

#52716

Epoxy on bottom of SMT component | 30 November, 2007

Shy,

Our 5 and 6 mils stencils have home plate apertures and reduced by 10% and using SMT adhesive. Never had a problem with components non wetting like you have. I do believe that you are not screening enough paste, something about the dog bone apertures doesn't sound right.

Can you possibly show us a picture before PNP?

Check this out:

http://www.beamonoregon.com/aperture.asp

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habsfan

#52739

Epoxy on bottom of SMT component | 1 December, 2007

Shy

You should try SMT-5. First solder PTH comps, then apply paste with your pick and place and apply glue with ur screen printer and come back to place smd with pick and place and then reflow. You will get great results. Good luck

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Stephen

#52743

Epoxy on bottom of SMT component | 2 December, 2007

Does that work well with a "lights out" factory?

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shy

#52745

Epoxy on bottom of SMT component | 2 December, 2007

The idea for solder at bottom side is for component such as SOIC, QFP and chip. This solder is needed since not entire bottom component had glue. that's why we're combining both solder paste and glue and reflow at the same time.

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shy

#52746

Epoxy on bottom of SMT component | 2 December, 2007

Hi Habsfan, if we're mount the THP first, we can't run SMT due to tTHP is tall and big which will causing the PNP to be chaos. Btw, my solder paste location is more than glue location which (solder paste : glue) is 2:1.

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shy

#52748

Epoxy on bottom of SMT component | 2 December, 2007

Hi Dback, Kindly provide your e-mail then i'll give the current opening pracitce at my area.

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Loco

#52749

Epoxy on bottom of SMT component | 3 December, 2007

yigh, loose the glue, put paste on ALL bottom SMD components and cover ALL SMD components with peel off before wave.

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shy

#52750

Epoxy on bottom of SMT component | 3 December, 2007

Hi Loco, If i cover all the SMT component with peel off before reflow, it'll increasing downtime at my production site. To reduce the downtime, we had idea to add in the glue for component package 0805 and bigger.

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Steve Thomas

#52752

Epoxy on bottom of SMT component | 3 December, 2007

I thought you said that the parts that weren't wetting in reflow were the parts with epoxy.

The question I have is do they wet in wave solder, and if they do, why does it matter what happens to them in reflow? Conversely, if they don't wet in wave, reflow isn't your biggest problem.

Just to cover my bases, if you're masking those parts with a fixture for wave and THAT's why you need good reflowed joints, why would you put glue on them?

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Real Chunks

#52766

Epoxy on bottom of SMT component | 3 December, 2007

Eject-Eject-Eject!

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Steve Thomas

#52771

Epoxy on bottom of SMT component | 3 December, 2007

It's OK, I could quit if I wanted to.

*bites palm*

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Stephen

#52772

Epoxy on bottom of SMT component | 3 December, 2007

Don't listen to Habsfan. He probably even thinks the Habs have won the Stanely cup. They've never won one.

They've been given a few though.

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shy

#52774

Epoxy on bottom of SMT component | 3 December, 2007

Q: I thought you said that the parts that weren't wetting in reflow were the parts with epoxy. A: Yes you're correct.

Q: The question I have is do they wet in wave solder, and if they do, why does it matter what happens to them in reflow? A: Yes, but somebody here don't agree with me that the glued part need help from wave to get the good wetting.

Q: Conversely, if they don't wet in wave, reflow isn't your biggest problem. A: Yes you're correct. But somebody here want this non- wetting issue settle at SMT.

Q: Just to cover my bases, if you're masking those parts with a fixture for wave and THAT's why you need good reflowed joints, why would you put glue on them? A: Some of the component is near to the THP and that'why i've got to glued the component. Btw, to save time of masking & fixture, we using glued to make the component stand off the wave which will be done a good job to make fillet at the component terminal.

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Steve Thomas

#52783

Epoxy on bottom of SMT component | 4 December, 2007

They are wrong. The only good reason you should be gluing parts on is because you want to solder them with the wave or if you are doing double-sided reflow and you have heavy parts that would fall off on the second pass. In your case you would have to hand solder your through-hole to use that process.

There are too many complications with getting glue on pads, glue mixed with paste, parts placed too high because of dot profile, etc., to count on getting good reflow on parts held on with chipbonder AND solder paste.

Q: Conversely, if they don't wet in wave, reflow isn't your biggest problem. A: Yes you're correct. But somebody here want this non- wetting issue settle at SMT.

See above. You gotta tell us this stuff at the beginning. Everyone wanted to know why you were doing things the way you were from the outset. Now we know.

Ahhh, so they are not maskded by your fixture. Still, they need no paste and in fact it's depending on the paste that's causing your problems, not non-wetting in reflow.

Btw, to save time of masking & fixture, we using glued to make the component stand off the wave which will be done a good job to make fillet at the component terminal.

You lost me here. Are you using peelable mask instead of a fixture?

If you really want to reflow some parts and wave others, get a new paste stencil without apertures for the parts you're gluing on.

I have done what you're doing before as a trial. Print paste, dispense glue, place components, reflow/cure with a reflow profile. We used a glue that was spec'd for that profile. We did it because we didn't have a chip wave and wanted to try to ensure enough solder on SOT-23 packages. It didn't work well (got chipbonder in the paste...imagine that) and I convinced them to buy a chip wave.

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