Difference between solder paste No clean vs water-soluble

What is the difference between no-clean and water-soluble solder paste?

Sol­der paste plays a crit­i­cal role in the PCB [Print­ed Cir­cuit Board] assem­bly process, serv­ing as a vital com­po­nent in ensur­ing the reli­a­bil­i­ty of the pro­duced PCBs. Under­stand­ing the dif­fer­ences between var­i­ous types of sol­der pastes is essen­tial for select­ing the most suit­able option for spe­cif­ic assem­bly require­ments. There are many types of sol­der paste offered in the mar­ket, but our focus today will be on how the no-clean sol­der paste and water-sol­u­ble sol­der paste dif­fer from each other.

Water Soluble:

water-soluble, no-clean solder paste

Water-sol­u­ble sol­der paste, also referred to as “wash­able” or “Clean­able” sol­der paste, allows for the removal of flux residue with deion­ized water fol­low­ing the reflow process. The water-sol­u­ble sol­der paste is a tra­di­tion­al choice and is par­tic­u­lar­ly use­ful in appli­ca­tions where the removal of flux residue is nec­es­sary to mit­i­gate poten­tial risks to the cir­cuit board­’s reli­a­bil­i­ty and functionality. 

The removal of the flux is cru­cial since it is con­sid­ered to be an impu­ri­ty or con­t­a­m­i­nant on the cir­cuit board and, to op that off, expos­ing the cir­cuit board to mul­ti­ple water wash cycles could be risky unless the com­po­nents are com­pat­i­ble with the water wash­ing process­es. Using water-sol­u­ble sol­der pastes comes from the require­ments imposed by the design­er to low­er the risk of reli­a­bil­i­ty defects, espe­cial­ly for high-per­for­mance elec­tron­ic devices, and to ensure the cir­cuit board is free from not only flux but also from oth­er harm­ful particles.

No-clean Solder Paste:

water-soluble, no-clean solder pastes

The no-clean sol­der paste, also some­times known as “low solids flux” or “low acti­vat­ed flux” sol­der paste is bet­ter and more reli­able in the cir­cuit board assem­bly process as it leaves behind min­i­mal residue after the reflow process. The sol­id con­tent is between 2% to 4% typ­i­cal­ly. There are also ultra-low-solids flux­es with about 0.5% sol­id con­tent, designed for wave sol­der­ing process­es that oper­ate in a nitro­gen atmos­phere with extreme­ly low oxy­gen con­tent [<50 ppm oxy­gen]. The residues from the no-clean sol­der paste are designed to be non-cor­ro­sive, resinous residue around sol­der joints harm­less to the end prod­ucts. Hav­ing to use them is con­sid­ered to be cost-effec­tive and process-friend­ly as it elim­i­nates the need for a post-sol­der­ing clean­ing process, espe­cial­ly dense­ly packed SMD boards. 


In sum­ma­ry, the main dif­fer­ence lies in residue man­age­ment, with no-clean focus­ing on min­i­mal residues that don’t require clean­ing, and water-sol­u­ble focus­ing on residues that can be eas­i­ly removed with water-based clean­ing process­es. The choice depends on the spe­cif­ic require­ments of the appli­ca­tion and the capa­bil­i­ties of the man­u­fac­tur­ing process.

water-soluble, process, cleaning PCB board, reflow process, wave soldering
Sin­gle-lay­er mixed assem­bly using a water-sol­u­ble sol­der paste

CAPLINQ man­u­fac­tures both the no-clean and wash­able sol­der paste. The no-clean sol­der paste options are SP-SAC305 and SP-SAC307. The water-sol­u­ble sol­der paste option offered now is SP-SAC305-WS. These sol­der pastes are lead-free and designed for excel­lent print­ing capa­bil­i­ties that guar­an­tee high reli­a­bil­i­ty with a low icon­ic acti­va­tor sys­tem. Please find our oth­er sol­der paste port­fo­lio in our Sol­der Paste cat­e­go­ry.

We are con­stant­ly expand­ing our port­fo­lio and we can devel­op or intro­duce the most com­mon sol­der paste alloys. Con­tact us with your design lim­i­ta­tions and appli­ca­tion require­ments to see how we can help you move for­ward toward a more effi­cient and sus­tain­able future.

About Nathan Shumugam

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