HAND SOLDERING SPECIALTIES
SMT REWORK/REPAIR TRAINING AND CONSULTING
200 Sherland Avenue,
Mountain View, CA 94043-3927
Phone (415)964-0577
FAX (415)964-5248
EMAIL gregphs2@aol.com
3-9-96
The following was a report in response to an inquiry, about the use of RMA flux, for tinning the soldering iron tips.
First I would like to make you aware of the flux use requirements as stated in the ANSI/J-STD-001A. Section 4.2 of the J-STD-001A states that;
Flux must be tested and classified in accordance with J-STD-004, MIL-F-14256, or equivalent. Flux used shall conform to types R, RMA, WSF, or LR of MIL-F-14256; or types L or M of J-STD-004. When types WSF, LR, L, or M are used, data demonstrating compliance with the testing of Appendix D shall be available for review.
Inorganic acid fluxes Type H, and rosin Type RA fluxes may be used for tinning of terminals, solid wire and sealed components. Inorganic acid fluxes may be used for assembly soldering provided flux residues are removed. Type H or RA fluxes may be used for soldering of terminals, solid wire and sealed components when performed as part of an integrated fluxing, soldering, cleaning, and cleanliness test system and when either of the following conditions is met:
a. usage is approved by the user,
b. data demonstrating compliance with the testing requirements of Appendix E is available for review.
Only Type LR or LO shall be used for low residue soldering processes.
When liquid flux is used in conjunction with other fluxes, it must be chemically compatible with other fluxes and materials with which it will be used. The flux of cored solder shall be accordance with this paragraph. The percentage of flux in cored solder is optional.
The next information you need is what Types of flux are L and M. This information can be found in ANSI/J-STD-004 as follows;
The ANSI/J-STD-004, defines four types of flux, Inorganic, Organic, Resin and Rosin. These fluxes are further characterized by the activity level of the flux and flux residue. It is the flux activity level and Surface Insulation Resistance (SIR) that determine the cleaning requirements. The three levels of activity are:
L= Low or no flux/flux residue activity
M= Moderate flux/flux residue activity
H= High flux/flux residue activity
These types are further characterized using a 1 or 0 to indicate the presence or absence of halide in the flux.
Only types L0, L1, M0, and M1 pass the SIR test both cleaned and uncleaned.
The type H0 and H1 fluxes, although generally water soluble, require strict cleaning monitoring due to the corrosive nature of the residue, and the inability to pass the SIR test.
Paragraph, 6.3 Flux Activity, of the J-STD-004 provided an approximate, though not necessarily accurate, analogy between L, M, and H type fluxes with the traditional classes of rosin-based fluxes (R, RMA, RA, and RSA), as well as other fluxes such as water soluble or synthetic activated fluxes, the following guide line is offered:
L0 Type Fluxes - All R, Some RMA, Some Low Solids "No-Clean"
L1 Type Fluxes - Most RMA, Some RA
M0 Type Fluxes - Some RA, Some Low Solids "No-Clean"
M1 Type Fluxes - Most RA, Some RSA
H0 Type Fluxes - Some Water Soluble
H1 Type Fluxes - Some RSA, Most Water Soluble and Synthetic Activated
The cleaning requirements are outlined in paragraph 8.0 of the J-STD-001.
As you can see because you are tinning stranded wire you should be using an RMA flux. Also unless used strictly for touch-up prior to cleaning, Organic water soluble flux must have the cleaning monitored to assure complete removal of all flux residue, because of the activity level of the flux. This is particularly important for your high reliability products.
Based on the information contained in the Kester product literature I would recommend using the RMA 186 series flux, on Page 9, and wire solder RMA 285, on page 12. For the wire solder you may also find that if the No. 66 core is used on through-hole you may be able to avoid using extra flux. You may continue to use the Organic flux and solder for touch-up of wave soldered boards prior to cleaning.
Regards,
Greg Painter, President