When solder is applied to a pure metal surface, there will be strong attraction between the surface metal and tin (the solder). The resulting compounds have no reactive energy (the usual term is “passive”) and will not attract solder. The atoms of metals that are good electrical conductors are unstable they want to combine with other element(s) to share electrons. Note the emphasis on pure (elemental) metal. That force is interatomic attraction between pure surface metal and solder. Wetting requires a fourth force – positive and stronger than the sum of the other three. The sum of those three forces is negative, meaning non-wetting. Gravity helps wetting at and below where the solder is applied (into plated holes if hand soldering, for example) but works against wetting above the solder application point (fighting vertical fill of PTHs in wave soldering). Gravity: Think of it as weight, pulling towards the ground. Both forces work against solder wetting but are less consequential than surface tension.Ī third force (gravity) either helps or impedes wetting: Surface tension is the most powerful negative wetting force.įriction: Resistance as an object moves over the surface of another object is called “static friction” but friction also exists within liquids (“viscosity”). Solder’s surface tension is much stronger than water’s (and greater with lead–free solder than leaded solder) and causes solder to form a sphere (the well-known “solder ball”). Alcohol flattens and spreads easily while water tends to bead up. Then do the same with water (much greater surface tension). To see the difference, pour a little alcohol (very low surface tension) on a non-porous surface like glass. Some liquids have very low surface tension while others have higher surface tension. Surface tension: Atoms on the surface of a liquid are attracted to atoms within the liquid. Two forces work against solder flow and are called “negative wetting forces.” They are: (I prefer the term I learned in Britain: “dry joint.”)įour natural forces determine the amount of wetting. What many people call “cold solder” actually has nothing to do with lack of heat it is simply non-wetting. When solder flows over a surface like a component lead, it is said to “wet” the surface. As with most things related to soldering, that begins with wetting forces. Understanding flux requires comprehension of what it does. The second part will explain the various types and classifications for electronics fluxes as well as the parameters that should be taken into account when selecting flux for specific uses.
#Solder flux series
This is the first of a two-part series and explains the fundamentals of soldering flux.
#Solder flux how to
Part 2 will explain flux categories, how to read a flux manufacturer’s technical data sheet, and how to determine the best flux for various situations. The following, in plain English, is the heart of what users need to know about why flux is needed, the ingredients of flux and what they do, and general issues. Even the terminology can be impenetrable.
#Solder flux free
The truly meaningful literature about flux (some of it free on the Internet but often behind paywalls) is written by chemists for chemists and completely unintelligible to the people who actually use the flux. (Beware of “neutral pH” flux.) Anyone who knows enough to distinguish between what is valid and what is junk probably doesn’t need the research. Dozens of manufacturers each sell dozens of flux formulations, almost all of those formulations being proprietary secrets that the customer won’t know, and they all post-marketing materials making claims that can be misleading and, in some cases, fraudulent. Unfortunately, most (not all, but most) of the free advice is worth exactly what it costs.
(Jim) Smith, PhD ABD, President, Electronics Manufacturing Sciences, no shortage of articles about flux on the Internet. And perhaps nothing is more important than understanding soldering flux selection and proper usage. The hard part is learning what makes soldering easy. So let me add this clarification: Perfect soldering is easy provided we make it easy.
However, most people who have not attended one of my Science of Soldering © classes do not find soldering all that easy and question my sanity.
0 kommentar(er)
