Water sol paste is definitely a minority sport, but is used in Class 3 MIL and avionics. It can be simpler to clean than many no cleans and makes sense in that regard if you would be cleaning anyway. I am a little out of touch now with US, but it used to be that West Coast people did more water cleaning proportionately than anywhere else. Probably a company cultural thing dating from the days of large mainframe computer people, probably the most complex assemblies then being made. Not forgetting that solderability was a novel concept in early days, so a bit of acid flux in the wave machine was handy when confronted with wooden boards. (Modern OA pastes are often little different in activity than no cleans however). Basically "If IBM/NCR/Burroughs etc do it then it must be OK" . NO benefit is without a cost and in the case of water sol fluxes, the costs of simplified cleaning are typically in reduced paste out times compared to regular pastes and in possible difficulties associated with cleaning delays. The biggest down side is your product's short working life if assemblies miss cleaning or are poorly cleaned. Like from years to weeks. So far as "recommending a good one" is concerned, you need to be aware that water sol pastes are much more varied in performance than RO and RE types. The formulation routes can be quite different according to supplier. This means you need to do a more robust evaluation of materials and process compared to no cleans. Some pastes will tolerate delayed cleaning (for example when you are batching up boards for off line cleaning); others might foam in inline cleaning. This can be affected by machine type as well as paste type. You will also need to keep in mind that Sod's Law (AKA Murphy's) is at a higher potential than usual. So you need to do a more FMEA type approach when establishing your SOP. Eg what happens if boards are not cleaned, which when it occurs, definitely will be over a long holiday weekend. Don't forget also to evaluate complementary products like cored solder wire and gel fluxes for repair and off line oddball components etc. Regards Mike -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls Sent: Wednesday, February 26, 2014 3:53 PM To: [log in to unmask] Subject: Re: [TN] Class III Solder paste, Sn63, Water Soluble Bob, You have to read the whole section to understand the requirement. You can't use a type IN (inorganic) flux to solder assemblies. Way too dangerous unless you REALLY know what you are doing, and even then.... So, you can use water soluble fluxes, which fit in the OR designation in most cases, but if it is a halide-bearing (which is the L1 designation) flux, it is too active to be used as a low solids / no-clean flux. If your water soluble flux is ORL1 or higher (e.g. ORM0, ORM1, ORH0, ORH1) you can still use it, but it has to be cleaned and you as the manufacturer have to have objective evidence that you clean sufficiently well to prevent electrochemical failures. That's what the "data demonstrating compatibility" means. If anyone is interested, I wrote a white paper for the IPC, which will be included as an appendix in IPC-J-STD-001 Rev F (sometime later this year), which discusses what "objective evidence" and "compatibility testing" means. The upcoming J-STD-001, Rev F, as it stands now in draft, would point you to IPC-9202 as one possible way to show compatibility. Did I answer your question or neatly rhumba around it? Doug Pauls From: Bob Wettermann <[log in to unmask]> To: <[log in to unmask]> Date: 02/26/2014 09:24 AM Subject: [TN] Class III Solder paste, Sn63, Water Soluble Sent by: TechNet <[log in to unmask]> Technetters: According to the JSTD "Flux shall not (N1N2,Defect Class 3) conform to flux activity levels L0 and L1 of flux materials rosin (RO), resin (RE) or organic" That being said who is doing class III work, complying with JSTD Class III requirements and using a water soluble Sn63 paste? (Our std does not comply) Can someone recommend a good paste? Bob Wettermann BEST Inc ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________