Soldering: Complete Soldering Guide, Tips and Techniques

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Electronics >> Soldering

Soldering: All about soldering including, hand soldering, thru-hole soldering, SMD soldering, wave soldering selective soldering, RoHS, Lead-Free (Pb-Free), BGA Soldering and Rework, Desoldering, Solder Wire, Solder Flux, Solder Bar, Soldering Technology, How to Solder and more.

Soldering is accomplished by quickly heating the metal parts to be joined, and then applying a flux and a solder to the mating surfaces. The finished solder joint metallurgically bonds the parts forming an excellent electrical connection between wires and a strong mechanical joint between the metal parts. Heat is applied with a soldering iron or other means. The flux is a chemical cleaner which prepares the hot surfaces for the molten solder. The solder is a low melting point alloy of non ferrous metals.

Proper soldering technique and quality of solder are the lifeline of any PCB manufacturing and assembly. If you are into electronics, you must be knowing that soldering is basically a technique to join two metals using a third metal or alloy.

In electronic PCB Manufacturing, assembly and rework, the metals to be joined are the leads of the electronic components (thru-hole or SMD) with the copper tracks on the PCB. The alloy used to join these two metals is solder which is basically tin-lead (Sn-Pb) or tin-silver-copper (Sn-Ag-Cu).

Tin-lead solder is called leaded solder because of the lead present in it while the tin-silver-copper solder is called lead-free solder because no lead is present in it. The solder is melted using either a wave soldering machine or a reflow oven or a normal soldering iron and this molten solder is then used to solder the electronic components on to the PCB. A PCB or Printed Circuit Board after assembly of electronic components is called PCA or Printed Circuit Assembly.

Few other terms such as brazing and welding is often linked with soldering. But one should remember that soldering, brazing and welding are different from each other.

Soldering is done using solder while brazing is done using a lower melting-temperature filler metal. In welding, the base metal also melts while joining two metals whereas this is not the case with soldering and brazing.

Before we proceed with soldering, let us understand some of the basics:

RoHS: Restriction of Hazardous Substances [ lead (Pb), mercury (Hg), cadmium (Cd), hexavalent chromium (CrVI), polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE).]

WEEE: Waste from Electrical and Electronic Equipments.

Lead-Free Solder: Solder with NO Lead (Pb).

Static electricity or ESD is an electrical charge that is at rest. This is mainly created by an imbalance of electrons that stay on a specific surface, or in the environmental air. The imbalance of electrons (in all cases, is caused by absence or surplus of electrons) thus causes an electrical field that is capable of influencing other objects at a distance.

Flux – Types and Role of Flux in Soldering: Flux plays a vital role in any soldering process and electronics PCB manufacturing and assembly. Flux removes any oxide and prevents oxidation of metals and hence helps in better soldering quality. There are basically three types of Flux used in Electronics:

1. R Type flux - These flux are Non-Activated and are used where there is least oxidation.

2. RMA Type Flux - These are Rosin Mildly Activated Flux. These fluxes are more active than R-Type fluxes and are used at places where there is more oxidation.

3. RA Type Flux - These are Rosin Activated Flux. These are very active flux and are used at places that have too much oxidation.

Solder – Types and Role of Solder in Soldering: Solder is the life and blood of any PCB. The quality of solder used during soldering and PCB assembly decides the life and performance of any electronic machine, equipment, appliance or gadget. Different alloys of solder are available but the real ones are those that are eutectic. Eutectic solder is one that melts exactly at the temperature of 183 Degree Celsius. An alloy of tin and lead in the ration 63/37 is eutectic and hence 63/37 tin-lead solder is called eutectic solder. Solders that are non-eutectic will not change from solid to liquid at 183 Degree Celsius.

Solder is available in various forms:

1. Wire: These are called solder wire and are available in various combinations of alloy and in various diameters ranging from 0.2 to 1.5mm. Solder wire is basically used in hand soldering.

2. Solder Bar: Solder bars are in the form of bar is sizes of .5 to 1 kg. Solder bar is used in wave soldering.

3. Solder Preforms: As the name suggests, these are solder in predefined shapes and sizes depending on the soldering requirement. They can be circular, triangular, rectangular or square or in any other shape.

4. Solder Paste: These are soldering in paste form. Solder paste is used in Reflow Soldering and Hot Air Soldering.

5. Solder Balls: These are solder in the form of tiny balls in sizes ranging from 18 to 30 MIL. Solder balls are used in BGA of Ball Grid Array soldering. Most of the tiny gadgets have BGA.

Electronic Components: There are two types of electronic components - Active and Passive.

Active components are those that have gain or directionality. E.g. transistors, integrated circuits or ICs, logic gates.

Passive electronic components are those that do not have gain or directionality. They are also called Electrical elements or electrical components. E.g. resistors, capacitors, diodes, Inductors. Again, electronic components can be in thru-hole of SMD (Surface Mount Devices or Chips).

soldering can be done the 3 ways:

1. Wave Soldering : Wave soldering is done for mass production. Equipments and raw materials needed for wave soldering are - wave soldering machine, solder bar, flux, reflow checkers, dip tester, spray fluxers, flux controller.

2. Reflow Soldering: Reflow Soldering is done for mass produuction and is used for soldering of SMD components on to the PCB. Equipments and raw material needed for reflow soldering are - Reflow Oven, Reflow checker, stencil printer, solder paste, flux.

3. Hand Soldering: Hand soldering is done in small scale production and repair and rework of PCB. Equipments and raw materials needed in hand soldering are - Soldering iron, soldering station, solder wire, solder paste, flux, desoldering iron or desoldering station, tweezers, solder pot, hot air system, wrist straps, smoke absorbers, static eliminators, heating gun, pick-up tools, lead formers, cutting tools, microscopes and magnifying lamps, solder balls, flux pen, Desoldering braid or wick, desoldering pump or sppon, overcoat pen, ESD material.

4. BGA Soldering: Another form of electronic components are BGA or ball Grid Array. They are special components and need special soldering. They do not have any leads coming out , rather they used solder balls used under the component. Because the solder balls have to be placed under the component and soldered, soldering of BGA becomes a very difficult task. BGA Soldering need BGA Soldering and rework Systems and solder balls. Read More about BGA.