Technetters,
Years ago after trying to define a process to be used by contract manufacturers I realized that what flux is used does not matter in the end for our products.. If peanut butter worked as a flux, fine. But when I get the boards they must meet the IPC board cleanliness specification. So our drawings now call out the type of solder tin/lead or lead-free and a cleanliness spec, no flux specified. With many different assembly applications such as submerged in dielectric oil, potted in RTV, conformal coated or used bare it would become a nightmare to manage. I don't think many CMs would want to empty and clean out their fluxing system (assuming wave) to run a special flux you specify. I can't speak to screening solder paste. How much of a pain to switching between different solder pastes?
For our space contract we are stuck with following what is in the contract and have to find ways to comply without having multiple lines for different products. But then we are not making 10,000 pieces a week.
I do agree that there should be something to clearly define each of the flux types along with their pros and cons without a manufacturer's slant towards their products. Also to consider is what machines you have in your process line or which machines you are planning to buy regarding application method, pre-heat method, post solder cleaning requirements and end use. None of this can be determined quickly.
One thing I did was to use solder and flux (wave system) from the same manufacturer to eliminate finger pointing is a problem arose.
Sometimes the non-scientific solution is dependent on which manufacturer's sales engineer makes the effort to visit and take you out for a nice lunch.
Phil Nutting
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Understood 😊 I'm not quite the newbie as I once was, now approaching 25 years in the electronics field.
Paul, you question regarding the young colleague is similar to the situation that I've found myself about 10 years ago. I spent some time looking for flux classes due to some "learning opportunities " we had to help flesh out my understanding of flux families to avoid further "opportunities". I was just able to find literature from vendors and the J-Stds.
Vendor info can be helpful, but one has to understand it's coming from their business perspective, some of it was out of my depth, and generally it all seemed more focused on the metallurgy than the flux. I would have liked even a primer class on the different materials, though finding the Printed Circuits Handbook did also help. But there are so many pros/cons with each type/application/cleaning of each flux that it can be hard for someone that doesn't deal with it day in and day out to digest. It really is an art and a science.
Around 2014 was when I found the IPC Cleanliness and conformal coat conference which helped and I was also introduce to this forum at that time.
But it does appear that flux can often be overlooked until it becomes a problem. And most designers and engineers who spec it (or don't spec anything at all) are really at the mercy of their vendors.
Jeffrey
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From: Stadem, Richard D <[log in to unmask]>
Sent: Thursday, February 27, 2020 1:41 PM
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You sure are welcome, Jeffrey.
And never, ever, start off a posting on this forum again with an apology for asking a dumb question. There are no dumb questions, and even after 45 years in this business I (and all of us) are just as much of a "newbie" as you are! There is simply too much to learn.
Odin
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From: TechNet <[log in to unmask]> On Behalf Of Jenkins, Jeffrey (US)
Sent: Thursday, February 27, 2020 3:08 PM
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Doug and Richard,
Thank you both very much I do appreciate both of your assistance. Something in the back of my mind (probably from IPC Cleanliness conferences!) said it’s not the best thing to do. I also went and pulled the IPC-CH-65 Paul had mentioned prior and I look forward to reading it.
Best,
-Jeffrey
From: Douglas Pauls <[log in to unmask]>
Sent: Thursday, February 27, 2020 12:55 PM
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Subject: Re: [External] [TN] No-Clean (ROL0) question....
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Jeffrey,
I will send you a document that I drew up about 12 years ago, together with the late Dr. Bill Kenyon. It talks about no-clean fluxes and why someone would choose to clean a no-clean flux. You might find it of benefit.
There are also a number of excellent papers by Dr. Mike Bixenman of Kyzen on the nature of fluxes under QFNs that more addresses what can happen if those low solids residues do not get to the proper temperature.
Douglas Pauls | Principal Materials and Process Engr | Advanced Operations Engineering COLLINS AEROSPACE
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On Thu, Feb 27, 2020 at 2:21 PM Jenkins, Jeffrey (US) <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Fellow TechNetters,
I apologize if this may seem like a newbie question and if so I apologize.
I've used OR fluxes and RO fluxes and have always had them removed by the cleaning process as most of the products that I work on have an expected life of 10+ years. We've typically validated the amount of WOA and Chlorides and set baselines for those.
Someone posed me a question about cleaning no-cleans. Even though in a perfect world a no-clean flux should be 100% inactive after reflow, I'm betting that's never perfectly the case. So my view and response was that based on the life span and end use environment, my concern would be humidity/moisture mixing with the residual material and in the long term increasing the risk of dendritic growth and other things. Am I off the mark?
Thanks,
Jeffrey A. Jenkins, CID+
Principal Engineering Designer
Cubic Mission Solutions
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