History of Soldering – an Art and a Science

Sol­der­ing can be viewed as both an art and a sci­ence.

Sol­der­ing as an art stretches back over 4000 years. Rem­nants of sil­ver sol­dered joints have even been found on vases dat­ing back to 2000 –3000 BC.Sol­der­ing as a sci­ence de­vel­oped dur­ing the 19th cen­tury. Soft sol­der­ing with lead and lead al­loys has been prac­tised by crafts­men for cen­turies. Due to the in­ven­tion of the can around 1900, a spe­cific alloy of tin and lead came to be used as the sol­der. By ex­actly match­ing the re­spec­tive quan­ti­ties of tin and lead, it was pos­si­ble not only to com­pletely seal the cans ef­fec­tively but also to ex­plain the con­nec­tions sci­en­tif­i­cally.

Thanks to the in­dus­trial up­swing in the 20th cen­tury, sol­der­ing has firmly es­tab­lished it­self as a man­u­fac­tur­ing process. Elec­tri­cal en­gi­neer­ing and elec­tron­ics owe their rapid growth not least to the re­search con­ducted in the de­vel­op­ment of sol­ders and fluxes tai­lored to meet in­dus­try needs.Today, soft sol­der­ing is the most well-known method of join­ing metal­lic ma­te­ri­als for elec­tri­cal sol­dered joints. (So-called hard sol­der­ing or braz­ing is men­tioned here for the pur­pose of com­plete­ness only).

General Notes on Soldering

Soldering: Joining metallic materials by means of a metal alloy (solder) with the application of heat is known as soldering. Here the melting temperature of the solder is lower than that of the metal parts to be joined, i.e. the metal parts remain in a solid state during the soldering process while the molten solder flows between the metal parts. The solder cools to leave a strong, tight, electrically conductive and heat conducting joint.

Lead-free soldering with Weller soldering equipment: Lead-free sol­der­ing re­quires more power as the melt­ing tem­per­a­ture is 30 to 40°C higher than leaded sol­der. The new Weller tech­nol­ogy is ide­ally suited to these spe­cial re­quire­ments. Lead free hand sol­der­ing re­quires sta­ble dy­namic tem­per­a­tures. To achieve this, sol­der­ing irons must have more power and an ef­fi­cient method of trans­fer­ring ther­mal en­ergy to the sol­der­ing iron tip.

Users of sol­der­ing irons that do not have these prop­er­ties at­tempt to over-come the prob­lems by run­ning the iron at an in­creased tem­per­a­ture to in­crease the ther­mal en­ergy stored in the tip. As soon as the tip is ap­plied to the joint, the ther­mal en­ergy is quickly dis­si­pated and be­cause of the sol­der­ing iron char­ac­ter­is­tics it can­not be quickly re­placed and the tip cools down.An ex­ces­sively high start­ing tem­per­a­ture poses con­sid­er­able dan­gers: Burn­ing of the flux, in­creased ox­i­da­tion of the sol­der­ing joint and dam­age to com­po­nents are pos­si­ble con­se­quences. The ser­vice life of the sol­der­ing tip is also re­duced.Weller sol­der­ing equip­ment gen­er­ates heat par­tic­u­larly quickly and also con­ducts it quickly to the sol­der­ing tip. Take ad­van­tage of our ex­per­tise and ex­pe­ri­ence. We will be pleased to help smooth your way into this new tech­nol­ogy.

Solder: The sol­der is usu­ally an alloy of two or more met­als. It joins met­als with the aid of heat. The tem­per­a­ture in­duces the sol­der to melt, but not the base metal. A good sol­der has the fol­low­ing prop­er­ties:

Moist­en­ing

The sol­der should flow eas­ily on the metal, at­tach to the metal sur­face or form an alloy. Nat­u­rally also in ex­tremely tight spots such as e.g. be­tween wires.

Tem­per­a­ture

The sol­der should al­ready liq­uefy at a rel­a­tively low tem­per­a­ture and moisten the metal.

Strength

The sol­der should be as strong as pos­si­ble, but with­out be­com­ing brit­tle.

Sol­der is avail­able in var­i­ous pack­age sizes and di­am­e­ters. The smaller di­am­e­ters en­able pre­ci­sion work to be car­ried out e.g. on printed cir­cuits.Many sol­ders have a con­tin­u­ous inner core or sev­eral cores. The core wires dif­fer, de­pend­ing on the ap­pli­ca­tion. The flux in a core wire is au­to­mat­i­cally me­tered in the cor­rect quan­tity. Sol­ders with­out an inner core wire are used to­gether with sol­der­ing flux.

Flux: Many met­als ox­i­dise with the oxy­gen in the air after a few sec­onds. This im­pairs the dura­bil­ity of the sol­dered joint. The flux ex­erts a clean­ing ef­fect and en­sures a per­fect sol­dered joint. The ox­i­da­tion layer on met­als dis­solves in the flux and evap­o­rates as soon as the flux has reached boil­ing point.

There are ba­si­cally two dif­fer­ent types of flux: or­ganic and in­or­ganic. Some or­ganic fluxes are used in elec­tric sol­der­ing while in­or­ganic fluxes are used in sheet-metal work­ing and in­stal­la­tion ap­pli­ca­tions. Most or­ganic fluxes are non­cor­ro­sive while in­or­ganic fluxes, in spite of their greater ef­fi­ciency, are cor­ro­sive to a cer­tain de­gree.

Organic colophonium or resin: Resins are gen­er­ally speak­ing or­ganic solids or liq­uids. Colo­pho­nium is the resin which yields a good non­cor­ro­sive and in­su­lat­ing flux.It is gen­er­ally un­nec­es­sary to clean elec­tri­cal com­po­nents be­fore­hand when using sol­der­ing wires with colo­pho­nium. Or­ganic fluxes with­out colo­pho­nium gen­er­ally sol­der bet­ter than those with colo­pho­nium, but do at­tack the base metal slightly on the other side. Clean­ing the work­piece be­fore­hand is rec­om­mended.In­or­ganic fluxes are vari­a­tions of acids and salts. They are highly ef­fec­tive but cor­ro­sive and are thus not suit­able for elec­tri­cal sol­der­ing joints. The ef­fect of these fluxes is so strong that even heavy metal parts can be sol­dered. They are only rec­om­mended to be used for rougher, non-elec­tri­cal joints. The sol­dered joint must be cleaned after sol­der­ing.