Shri Sant Gajanan Maharaj College of Engineering Department

Shri Sant Gajanan Maharaj College of Engineering Department of Electronics & Telecommunications Engineering Electronic Devices & Components Unit – III Printed Circuit Boards Manufacture, Development and Soldering Techniques Soldering and Desoldering Techniques

What is Soldering ? • Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal. • Soldering differs from welding in that soldering does not involve melting the work pieces.

Equipment for Soldering • Soldering iron • Soldering Wire • Rosin core solder • Well lighted work area • Clean work area

Equipment for Soldering • • Tip cleaner Exhaust fan Magnifying glass Panavise

Equipment for Soldering Iron Tips Magnifying Glass Soldering Iron & Stand Desoldering Wick Clamp [Penavise] Desoldering Pump

The Soldering Process

Equipment for Soldering

Soldering Iron Stands • These are handy to use if you are doing a lot of soldering. • It is a heat resistant cradle for your iron to sit in, so you don't have to lie it down on the bench while it is hot. • It can be essential if you are planning to do a lot of bench soldering as it is only a matter of time before you burn something (probably your elbow resting on the hot tip) if you don't use one.

Soldering Iron Types • Basic on/off • Basic temperature controlled • Digital temperature controlled

Soldering Iron

Soldering Iron • Typical power rating 15 W, 25 W • Used in technical education institutes where solder work is less

Soldering Iron There are several things to consider when choosing a soldering iron. • • Wattage Adjustable or fixed temperature Power source (electric or gas) Portable or bench use

Soldering Iron Types

Soldering Iron Placement

Soldering Iron Constant wattage Iron is continuously “ON” and eventually reaches equilibrium temperature 20 to 25 watt iron sufficient for circuit board assembly Constant temperature Tip incorporates a thermostatic element to maintain desired tip temperature 650 – 750 ° F appropriate for circuit board assembly

Temperature Controlled Soldering Station Feedback control maintains tip at desired temperature Adjustable, often with analog or digital temperature display Many have grounded tip to help prevent ESD damage

Types of Tips for Soldering Iron • Conical • Spade • Chisel

Types of Tips for Soldering Iron • Conical tips are better suited for soldering Surface Mount Devices (SMD) which have small size • Chisel tips are better suited for soldering regular components

Types of Tips for Soldering Iron Pointed tips cannot transfer large heat to component terminals and pads. They are also dirty and oxidized, which will further inhibit heat transfer. You’ll get better heat transfer if you have more surface area at the tips. Metcal SSC-7 xxseries tips (hot for lead-free) for their SP 200 soldering system. Bevel tip SSC-747 A Chisel tip SSC-736 A

“Clean” the tip by applying flux, then melting some solder right on the tip, then rub it off in the gold brillo. Repeat a few times. Bevel tip Chisel tip It should end up looking tinned like this.

Clamps [also known as Panavise] Clamps of some sort are strongly recommended. Trying to hold your soldering iron, the solder, and the wire is tricky enough, but when you have to hold the connector as well it is almost impossible. There are however, adjustable clamps that can be manipulated to hold both the connector and the wire in place so you still have two free hands to apply the heat and the solder.

Clamps [also known as Panavise] • Many models • Great for holding boards • Allow lots of movement

Clamps [also known as Panavise]

Clamps [also known as Penavise]

Clamps [also known as Panavise]

Clamps and PCB is firmly held by clamp and the hands remain free to hold soldering iron and soldering wire

Magnifying Glass After soldering components, a magnifying glass is used to observe quality of soldering. Defects like application of less solder, dry solder, solder bridge etc. can be detected

Safety First • While soldering do not shake the soldering iron, otherwise molten solder may fly into your eyes or on skin • While soldering ensure that no other person is standing in front of you • Do not hold soldering iron too close to your face • Wear safety Goggles • Work in a well-ventilated area • Do not put wires or solder in your mouth • Wash your hands when soldering process is over

Types of Solder • Solders are generally alloys that are designed to achieve certain properties. • Leaded – Sn 60/Pb 40 (MP=183 -190 C) – Sn 63/Pb 37 (MP=183 C) • Lead-free – Sn 96. 5 Ag 3. 5 (MP=221 C) – Sn 96. 5 Ag 3. 0 Cu 0. 5 (MP=217 -220 C) – Sn 99. 3 Cu 0. 7 (MP=227 C) – Sn 100 (MP=232 C)

Solder wire bundle

What is Flux? It is a chemical cleaning agent, flowing agent, or purifying agent

Constituents of Flux A flux may be solid, pasty or liquid, depending on how it is to be used. Its principal constituents are: 01] a ‘flux base’, together with 02] activators’ and 03] solvents. For most fluxes: • The solvent content aids flux (or paste) application, but is volatilised during the pre-heat stages of the soldering process • The flux base is fluid at soldering temperatures and has good heat transfer properties.

Why use Flux? The purpose of flux is to facilitate the soldering process. One of the obstacles to a successful solder joint is an impurity at the site of the joint, for example, dirt, oil or oxidation. The impurities can be removed by flux, but the elevated temperatures required to melt the filler metal (the solder) encourages the work piece (and the solder) to re-oxidize. This effect is accelerated as the soldering temperatures increase and can completely prevent the solder from joining to the workpiece.

Why use Flux? • Reduces oxides on all surfaces involved in the solder connection • Reduces surface tension of molten solder • Helps prevent reoxidation of surfaces during reflow • Assists in transfer of heat to solderable surfaces

Types of Fluxes • Fluxes clean the surfaces and promote wetting • Rosin Fluxes – RMA (rosin, mildly active) most commonly used – Leaves sticky residue that must be cleaned with solvents (i. e. alcohols) • Water Soluble Fluxes – Flux residue is removable with hot water • No-Clean Fluxes – Flux residue can be left on board – Inert and “visually acceptable”

Fluxes Packages • Flux delivery – – Flux-core solder Flux pens Tacky flux Solder paste

Flux-core solder Most solder used for electronics assembly is in wire form, with the flux incorporated inside the solder. Multi-core solder has several (usually five) separate flux channels within the solder. For circuit board assembly use wire solder with a diameter of about 0. 025 inch or less

Soldering Process Heat soldering iron Clean tip Tin tip Apply heat and solder to component Touch soldering iron to one side of pin, touch solder to the other side of the pin • Allow solder to flow • Remove soldering iron briefly and retouch • • •

Preparation for Soldering Solder Pads Top View Side View Circuit Board Resistor

Step- 01 Tinning the iron - Tin the tip of the soldering iron by melting an inch or so of solder on the tip. - The iron will now look shiny on the tip. - Then wipe any excess solder on the golden sponge. - Now place the iron back into the holder. Tinning your soldering iron in this manner will aid in future soldering.

Tinning the iron

Soldering Iron

Move soldering iron until tip is touching wire & solder pad

Move solder to touch edge of tip. Solder

Hold until solder melts on tip by wire Solder

Move solder back to touch wire only Solder

Move solder in to form a small pocket Solder

Move soldering iron tip up. This will drag solder up with it. Solder

Look for shinny fillets

Soldering Tips 1. Make sure tip is hot 2. Clean & tin tip 3. Keep tip clean by using wet sponge and cloth 4. Heat until the parts are hot enough to melt solde sold 5. Hold until solder flashes around pad 6. Do not put too much solder on

Tips for Soldering - Use caution when clipping leads to avoid flinging metal across the room. - All soldering must achieve a good solder filet on the pad as shown for circuit reliability. - Also clip the leads in this fashion. - Bend resistors and diodes using your plastic tool as shown. workmanship. nasa. gov Example of a good solder filet

Pre bending Use a lead bending jig, if available, to form the component leads to the correct spacing If a bending jig is not on hand, grasp the leads, not the body, of the component with needlenosed pliers and bend gently.

Pre-Bending: Pre-Bending 101: - Pre-bending is a technique that allows components to be easily inserted into a PCB. - Pre-bending also allows components to lay more flush with the board. - Bending components to the correct bend radius takes practice, but mastering the technique will reap rewarding benefits! 53

Pre-Bending: Pre-Bending 101: - Start with the bending and prodding tool in the position shown in the top picture. 90° 54 - Choose a location along the length of the tool that will yield the appropriate bend radius. - Use your thumb to bend the lead such that the component and lead are orthogonal.

Hands-on: Soldering 14

Electrostatic discharge (ESD) Potentials as low as 200 volts can cause damage to CMOC ICs and MOSFETs

Wrist strap Conductive work surface A workstation equipped to prevent ESD damage Wrist strap connection point

When ESD measures are not available Touch a known earth ground before touching circuits and components.

Prep Step 1: Tool Layout - Prepare tools for the construction process. - Put on your safety glasses.

Prep Step 2: Grounding - Put on a static strap to remain grounded. Also make sure the strap is tight across your wrist. - This will protect any parts from electrostatic discharge (ESD) and its harmful effects.

Prep Step 3: Soldering Station - Turn on the soldering iron - Set the temperature control on the soldering iron to a temperature about 300 °C - As a general rule use a temperature in the range between 550 and 650 degrees Fahrenheit.

Prep Step 3: Soldering Station

Cleaning Soldering Iron Soldering iron tip must be cleaned often during use. There are many cleaning solutions and the cheapest (and some say best) is a damp sponge. Just rub the soldering iron tip on it after each solder connection.

Prep Step 4: Tinning the iron - Tin the tip of the soldering iron by melting an inch or so of solder on the tip. - The iron will now look shiny on the tip. - Then wipe any excess solder on the golden sponge. - Now place the iron back into the holder. Tinning your soldering iron in this manner will aid in future soldering.

Prep Step 4: Tinning the iron (close-up)

Soldering Components of Mini Project Step 1: Take up solder kit

Soldering Components of Mini Project Step 2: Layout kit (Socket not shown)

Step 3: Look at board, find reference point Component Side

Step 3: Look at board, find reference point for IC Solder Side

Step 4: Flip board over and solder 8 pin socket Step 5: Install 555 timer. Small circle placed over pin hole “ 1”

Step 6: Flip board over and bend chip leads out

Step 7: Install 120 kΩ resistor (Brown, Red, Yellow)

Step 8: Install 33 kΩ resistor (Orange, Orange)

Step 9: Verify resistors 120 kΩ Brown, Red, Yellow 33 kΩ Orange, Orange

Step 10: Flip board over Resistors 120 kΩ Brown, Red, Yellow Step 11: Solder 33 kΩ Orange, Orange

Step 12: Inspect solder joints and trim leads

Step 13: Flip board over and install capacitor Gray strip indicates “negative” lead “-” Lead

Step 14: Verify capacitor is installed correctly “-” Lead

Step 15: Flip over board and solder capacitor “-” Lead

Step 16: Verify solder joint and clip leads

Step 17: Install RED LED over 120 kΩ Resistor Negative side is facing edge of board Negative Lead

Step 18: Install GREEN or YELLOW LED over 33 kΩ Resistor. Negative side is facing edge of chip Negative Lead

Step 19: Flip board over and solder LED leads

Step 20: Solder chip to board. Go slow Step 21: Verify solder joints and check for solder bridges

Step 22: Install 9 V battery clip to board 35

Step 23: Flip board over and solder battery leads

Step 24: Attach test battery and watch what you made

Soldering a Component Insert the component’s leads through the holes in the circuit board. The body should lie flat against the board without having to force it down. Turn the board over and gently bend the component leads outward to hold the component in place

Soldering a Component Clean the iron tip by wiping on a damp sponge. Tin the tip by applying solder, then wipe again. Apply the iron in contact with both the circuit board pad and the component lead. Apply solder to the joint, not to the iron, and allow the heated joint to melt the solder

Soldering a Component Use a pair of flush-cutting wire cutters to cut off the excess lead length as close to the board as possible. Hold the lead so will not fly away when cut, a possible occasion for eye injury. !! WEAR SAFETY GLASSES !! Good soldering Inspect the soldered and trimmed lead. It should be uniform and shiny, with no cracks, gaps, or graininess. Bad soldering

Basic Requirements • Clean metal surfaces • Clean, tinned soldering iron • Correct solder and flux • Correct temperature and time The actual methods used depend on the tools and materials at hand, the physical nature of the parts and boards, and the skill of the worker.

Cleaning with wire brush Tinning the iron Cleaning by wiping tip on a damp sponge

A diameter of 0. 025 inches is common for most electronic work. Eutectic alloy (lowest melting point) 63% tin, 37% lead

Summary of Soldering Process Apply the iron, then the solder. Remove the solder, then the iron. (About 3 seconds per lead)

Tools and Materials for Soldering

Temperature controlled iron with grounded tip

A magnifier is helpful for inspection Circuit board holder Solder bridge

Defects in soldering Soldered Top View Solder bridge shorting two traces But, can be fixed by reheating or using solder sucker

Defects in soldering

Defects in soldering

Examples of Bad Soldering • Dry Joint • Needs more solder.

Examples of Bad Soldering • Cold Joint • Parts moved while solder cooled.

Examples of Bad Soldering • Cold Joint • Wire was not held in place.

Examples of Bad Soldering

Examples of Good Soldering

Good Solder Practice

Examples of Good Soldering • Note the lug's hole is full and the surface is shiny all around

Desoldering • Desoldering wick • Desoldering Pump • Desoldering iron

Desoldering Methods Desoldering braid Vacuum pump Vacuum desoldering station

Desoldering Pump (dismantled)

Desoldering Wick before desoldering process Desoldering wick bundle Wick after desoldering process • The wick is made by twisting together fine copper wires • Solder flows on to the wick by capillary action during desoldering process

Desoldering Wick Solder wick is a twisted mesh of thin copper wires that is placed on a joint and when it heats up it also melts the solder which is drawn out of the joint. It is usually used for cleaning up solder from tracks on a circuit board, but you will need a solder sucker to clean out the holes in the circuit board.

Desoldering Wick Place the wick on the solder you want to remove then put your soldering iron on top of the wick. The wick will heat up, then the solder will melt and flow away from the joint and into wick.

How to use desoldering wick? • The solder will flow into your wick and the wick will turn silver with solder • This may take a while, be patient and apply constant contact with the iron • Try rolling the soldering iron along the wick if you’re really having trouble • You might also want to try cleaning your iron if it isn’t working

Using desoldering Wick

Desoldering using Vacuum Pump

Cleaning solder traces after removing an IC Cleaning of pads with desoldering wick

Removing a solder bridge with braid

Clean the area Spray with flux cleaner and then brush to remove flux residue.

Desoldering Example An example of removing capacitor from a PCB Tools needed for Desoldering

Desoldering Example An example of removing capacitor from a PCB Clean Soldering Iron Tip

Desoldering Example An example of removing capacitor from a PCB This capacitor will be desoldered

Desoldering Example An example of removing capacitor from a PCB Clean the terminals Wetting toothbrush with Isopropyllic Alcohol Clean the components terminals Cleaned terminals

Desoldering Example An example of removing capacitor from a PCB Apply fresh solder to the two terminals Soldering one terminal Pushing the terminal forward with Soldering iron tip Soldering other terminal Pushing the terminal backward with Soldering iron tip

Desoldering Example An example of removing capacitor from a PCB Desolder the component Hold desoldering pump Correct way of holding soldering iron Correct way of holding desoldering pump Desoldering by releasing the lever

Desoldering Example An example of removing capacitor from a PCB Repeat process of desoldering and pushing Terminals after first soldering round Pushing the terminal forward with small screwdriver Pushing the terminal backwards with small screwdriver Terminals after desoldering process

Desoldering Example An example of removing capacitor from a PCB Remove the component Remove by pulling component with fingers Component removal complete Component is free and is bein pulled out

Desoldering Example An example of removing capacitor from a PCB Cleaning part of PCB from where component was desoldered Residue of flux (brown colour) is seen After using the screwdriver Removing residue with small screwdriver Cleaning board with Isopropyllic Alcohol

Desoldering Example An example of removing capacitor from a PCB Cleaning part of PCB from where component was desoldered Cleaning component side How component side looks after removal of capacitor How solder side looks after removal of capacitor