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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Bubbles on solder joint(after conformal coating curing)

Views: 10727

Hi All, Recently we are working on the conformal coating ... - Nov 19, 2009 by TMS78  

#60478

Bubbles on solder joint(after conformal coating curing) | 19 November, 2009

Hi All,

Recently we are working on the conformal coating process using Humiseal chemical 1B73 and thinner 521.

Bubbles on component body/joints are seen after gone through the IR Reflow Oven.

During the conformal coating, only tiny bubbles seen after coating.(the machine is fine,as able to dispense some chemical without bubbles using beam mode)

After staging, the tiny bubbles are gone. Very nioe finishing. But bubbles seen after the IR Curing Reflow Process.

Caused of bubble;;; Suspected 1 :- the tiny bubbles are entrapped into the components body gap which erupted after curing..

Anyone have any experenice in conformal coating process which is able to help advice :

1) is our suspected cause vaild ? - even we do 24hrs environment curing, the bubble still exist..

2) anyway to eliminate the bubbles issue ?

21 Dec 09-Update : Hi All,

We have managed to clear most of the bubbles issues on most of the components:- with the help and advice from everyone that contributed in this forum.. Really appreciate the advice.

The only isssue that we are seeing now is mainly along the IC Lead - i have attached a picture of the Chemical merging/form along the IC lead. Can anyone advice is the chemical merging along the IC lead acceptable. Is that consider as Bubbles (although it look like it is)?

Attachments:

reply »

#60497

Bubbles on solder joint(after conformal coating curing) | 19 November, 2009

Since the bubbles: * Are only on the solder connection, we'd guess there must be some compatibility issue between the flux residues and the conformal coat materials. * Occur after curing, we'd guess the cure recipe is too rapid and is entrapping volitiles.

reply »

#60526

Bubbles on solder joint(after conformal coating curing) | 22 November, 2009

Hi The bubble shows only around component body after ir reflow. I think bubble means that there is a moisture. How do you dry the PCB(?) before IR reflow?

Thanks Ju-young.

reply »

#60527

Bubbles on solder joint(after conformal coating curing) | 22 November, 2009

Hi Ju Yong,

The PCB are dry in an airseal cabinet(Staging Chamber) before IR Oven. The bubbles show at around body and solder joint area.

You mean the moisture will create bubbles ? Able to advice the humidity and temperature that you are using in the staging chamber ?

reply »

#60528

Bubbles on solder joint(after conformal coating curing) | 22 November, 2009

Hi Davef,

The bubbles occurs at the body also...there's also a washing process before the conformal coating:-the Flux residue are removed after washing. ... The curing profile is also something that we are looking into during the initial troubleshooting,but even we eliminate the Oven curing,by using environment curing, the bubbles still exist...

What chemicals have you been dealing with on the conformal coating ?

reply »

#60532

Bubbles on solder joint(after conformal coating curing) | 23 November, 2009

Search the fine SMTnet Archives [use => confo* and bubb*] to fine threads like: http://www.smtnet.com/Forums/Index.cfm?CFApp=1&Message_ID=59681

reply »

#60540

Bubbles on solder joint(after conformal coating curing) | 24 November, 2009

Hi Davef,

Thanks...Saw 1 of your thread that you posted : Thanks for providing...

From davef : There are many possibilities: * Conformal coat is incompatible with surface residue on the board * Conformal coat is incompatible with solder mask on the board * Moisture is out-gassing from the board * Conformal coat is too thick and does not allow the gaseous products to get out [your operator's theory] * Thinner is evaporating too quickly to allow the bubbles to escape * Coating is being cured at too high of a temperature that causes the surface of the coating to skin over and trap the volatiles inside of the conformal coating

reply »

#60566

Bubbles on solder joint(after conformal coating curing) | 25 November, 2009

Why in heavens name are you using a heat or air cure conformal coating. Why aren't you using a 100% solids UV cure system. You would never have an issue like this

Sam Forman MicroCoat Technologies

reply »

#60572

Bubbles on solder joint(after conformal coating curing) | 29 November, 2009

Hi sforman1,

The chemical that i'm using is a solvent based coating humiseal 1B73. From my understanding,the UV curing is mainly for UV curable coating like the UV40.

And the main advantage of using UV curing is for fast throughput and environment issue...

Don't think it will eliminate the bubbles issue as UV curing is more moisture and chemical resistance as well.

reply »

#60574

Bubbles on solder joint(after conformal coating curing) | 30 November, 2009

totally wrong. a. I do not reccomend Humiseal UV products. My Dad started Humiseal. b. As the former VP of Dymax Corporation I know quite a bit about this subject. Contact Dymax in Torrington, CT and inquire about 984LV. c. You will definetly sleep better :)

Sam Forman

reply »

#60580

Bubbles on solder joint(after conformal coating curing) | 30 November, 2009

Hi sforman1

Are you refering that the UV is able to cure on solvent based material too ?

reply »

#60585

Bubbles on solder joint(after conformal coating curing) | 1 December, 2009

What solvent based material. Call me at 972-678-4950. I have been doing this for >40 years. no cost to you. just trying to help

Sam

reply »

#60592

Bubbles on solder joint(after conformal coating curing) | 2 December, 2009

UV40 for you info was developed in Humiseal EU and has been tested heavily against Dymax product. UV40 is a great product has many approvals from major auto and whitegoods makers....

I have seen comparisons UV40 to Dymax 984LV and Dymax comes out second best....

reply »

#60595

Bubbles on solder joint(after conformal coating curing) | 2 December, 2009

Josh: This is your choice. It wouldn't be mine. Again, I have been doing this for well over 40 years (http://www.m-coat.com)

Sam

reply »


Lou

#60596

Bubbles on solder joint(after conformal coating curing) | 2 December, 2009

As a large coating house we use 1B73 daily and we have very few issues with bubbles. We very rarely bake it as the air cure is so short. Also, we only use thinner 73 vice 521. Another question would be; how is it being applied? How thick are you applying it? We apply it mostly by hand spraying and hand brushing at about 3 mils thick.

reply »

#60602

Bubbles on solder joint(after conformal coating curing) | 2 December, 2009

Hi Lou,

we are using a fluid dispensing machine. our current requirement is around 50um.

From the Datasheet,the thinner 73 has a higher evaporation rate of 1.0 comapring with thinner 521 at 0.6...

does the higher evaporation rate eliminate the bubbles issue...?

how's your experience of the thinner 73 against 521 ? interested to know how is the constant thickness able to be achieved using manual spraying ?

reply »

tommyg_fla

#60702

Bubbles on solder joint(after conformal coating curing) | 18 December, 2009

dave, where I work they are having the same problems with 1B31 acrylic. The coating thickness is 6-8 mils dried so that have to do several passes with an air dry between them and a final oven cure. They think that it might be related to the heating rates in the Nordson oven. Stange that after several years that the problem is occurring. Any other ideas on troubleshooting? Can they look for moisture in nitrogen supply? Don't think that the PCB supplier or soldermask type has changed. They don't think it is coating related since other product with thinner coating requirements don't show the same fine bubbles after cure.

Thanks Tom

reply »

#60703

Bubbles on solder joint(after conformal coating curing) | 18 December, 2009

Tom: Once again - why are you using solvent based conformal coating. 1B31 is OK as a CC but it contains Toluene and MEK!! It is only 35% solids which means you are trying to get rid of 65% solvent. If you must use it due to customers requirement then be sure everything is absolutely clean and dry. Look at it this way. If you were painting your house would you put paint over loose material or dirty siding? Of course not. Using solvent based coatings means paying attention to details. Are you using "no clean" flux? If you are applying a coating over this look out for particles on the board that may trap moisture. I am a very big proponent of UV cure coatings. Look into them

Sam Forman MicroCoat Technologies

reply »


kpm

#60739

Bubbles on solder joint(after conformal coating curing) | 28 December, 2009

@tommyg_fla

According to the TDS the recommended coating thickness for Humiseal 1B31 is only 1-3 mils so if I had to guess I would say your issue might be that you're re-coating over the first pass too soon. All the solvent hasn't evaporated and then you're trapping it with the next pass. Then when you do an oven cure it rapidly evaporates the solvent causing bubbles in your coating. I could be wrong as I have no idea how long you're air drying between coats but its just a thought.

On another note the TDS says that it takes 24 hours at room temp or 30 minutes @ 170 degrees F for it to cure. It doesn't say if that's the recommended time between coats or not. I imagine you could contact Humiseal for their recommendations.

reply »

SMT Services - STI Electronics

ii-feed SMT Intelligent Feeder