Seven Tools for Soldering

Electronic circuits are improved through prototyping and experimentation, and manual soldering is an essential part of this process. Soldering is necessary when creating a board for delivery or when making modifications to a customer’s board. Soldering skills affect the final result of the board. Therefore, it is important to understand the proper way to perform soldering operations.

Soldering requires the tools shown in Figure 1. This article describes tools for soldering and rework, including an iron for melting solder, solder as a bonding material, and nippers for cutting component leads.

Figure 1: Tools for Soldering and Rework

Seven Essential Tools

1. Soldering Iron

The quality of construction and materials of soldering iron tips manufactured in Japan are superior. Two major Japanese manufacturers are Hakko Corporation (HAKKO brand) and Taiyo Electric Inc. Co. Ltd. (goot brand).

As a soldering iron is used, the iron’s heated parts, especially the tip, will oxidize and turn black. Oxidation makes it difficult to melt solder, so if the tip is even partially oxidized, it should be replaced immediately. If the oxides are removed and the tip is always kept clean, it can be used for more than one year.

Iron and Stand Kit Is Convenient for Beginners

Various types of soldering irons are available at DIY stores. The two most common types of irons are：

• ・nichrome heater type
• ・ceramic heater type

Ceramic heater irons are slightly more expensive than nichrome ones. For beginners, the X-2000E (goot brand), which includes a ceramic heater iron, an iron stand, and other accessories, is convenient.

Ceramic Iron with Temperature Control Is Recommended

A nichrome heater iron cannot maintain proper temperature. If budget allows, a ceramic iron with temperature control is strongly recommended.

With the temperature control function, you can always work at a temperature suitable for soldering. Even when working intermittently while checking drawings, soldering can be resumed without concerns about temperature.

Typical products are FX600 (HAKKO) and PX201 (goot). PX-335/PX-338 are also recommended. The temperature should be set at 360°C. It is more important to be able to maintain a constant heating temperature than to be able to continuously adjust the temperature with a dial.

Two Irons Are Useful for Chip Components

For removing chip components, it is convenient to have two irons so that the two pads of a chip can be heated at the same time.

One 40W Nichrome Iron to Prevent Heat Absorption in Solid Patterns

When soldering or removing components from a solid pattern with a large heat-absorbing area, a nichrome iron with a large heat capacity (approx. 40 W) is useful.

2. Soldering Iron Stand

If an iron stand that allows heat to escape easily is used, the temperature cannot be maintained even if the iron has a temperature control function.

Each nichrome iron and ceramic iron has its dedicated stand equipped with a cleaner. A sufficiently heavy stand that will not move when cleaning the iron tip is recommended.

3. Cleaner

The following two types are available.

• ・Sponge (moistened for use)
• ・Metal wire wool

4. Nippers

This tool is used to cut component leads after they are inserted into the PCB. Precision nippers made by tool manufacturers are available at DIY stores.

Good nippers have a pointed tip and are sharp enough to easily cut even leads stuck to the PCB. The tips are very delicate, so do not cut hard wires or the like (Figure 2).

Figure 2: Nippers with Nicked Edge

Popular nippers are the MN-A05 (Maruto Hasegawa Kosakujo Inc., KEIBA brand) and nippers from Fujiya Co., Ltd.

5. Desoldering Pump and Desoldering Wire

Both are used to remove components and excess solder.

Desoldering pumps are indispensable for rework on PCBs with through holes. Performance and ease of use are more or less the same for all manufacturers’ products.

Desoldering wires are commonly used to remove surface-mount components, but not many manufacturers produce them. A wide wire requires a soldering iron with a large heat capacity, so a thin wire is preferable.

6. Solder

Lead solder and lead-free solder are available. For experiments, we recommend lead solder, which is easier to work with.

Select rosin-core solder for PCBs, and not solder for sheet metal work (Figure 3). Rosin is also called flux.

Figure 3: Cross Section of 0.6 mm Diameter Rosin-Core Solder SE-56006 (goot)

Lead solder with a mixing ratio of 60% lead and 40% tin is easy to obtain and use.

Lead-free solder is difficult to obtain in small quantities. Hozan’s products come in three sizes, 0.3 mm, 0.6 mm, and 1.0 mm diameter, on bobbins with net weights of from 100 to 400 g.

The thinnest diameter is 0.3 mm and the thickest is 1.0 mm. 0.6 mm solder can be used for soldering all types of components, including surface mount components. Many people use both 0.8 mm and 0.3 mm.

7. Tweezers

Tweezers should fit comfortably in the hand.

Non-magnetic stainless-steel tweezers with pointed tips are easy to use. The left and right tips must be perfectly aligned when closed. Expensive, completely non-magnetic titanium tweezers are not necessary.

Among tweezers of various prices, K-10 (by KFI) is recommended for its good cost performance.

The tips are so delicate that they bend easily and become unusable. Do not apply force or drop them.

Other Tools

Magnifying glasses, screwdrivers, wire strippers, and other tools should be available as needed.

Soldering of Lead Insertion Type Components

This section describes the procedure for mounting an IC socket on a PCB (Figure 4) .

Figure 4: Soldering of IC Socket： IC Socket and PCB before Mounting

First, insert the IC socket into the PCB (Figure 5).

Figure 5: Insert IC socket into PCB.

Turn the PCB over and heat a PCB pad and a component lead with the iron for one to several seconds (Figure 6). With a conical tip, the temperature of the tip end does not rise high enough, so use a side of the tip. If solder does not adhere properly, try a flathead screwdriver-type tip.

Figure 6: Heat the pad and lead with the iron.

Without moving the iron, bring a solder wire between the pad and lead (Figure 7).

Figure 7: Bring solder wire and iron between the pad and lead.

Continue to feed the solder, making sure that the heated pad and lead suck in the molten solder (Figure 8). Do not move the iron during this process. The flux in the solder wire will allow the molten solder to spread naturally.

Figure 8: Continue to feed solder, making sure that the pad and lead suck in molten solder.

If the pace of solder feed is too fast, the flux heats up too quickly and the solder splashes out in small balls.

When the through-hole is filled with solder and the solder rises to form a mound at the tip of the iron, withdraw the solder wire (Figure 9). The iron must not be moved at this time.

Figure 9: When the through-hole is filled with solder and solder rises to form a mound, withdraw the solder wire.

Finally, lift the soldering iron straight up (Figure 10). If the solder is at the right temperature, the solder cools and hardens on the spot without being drawn to the iron. If a shiny, smooth, and concave cone is formed (Figure 11), the work is successful. However, shiny surfaces may appear on lead solder but may not on lead-free solder.

Figure 10: Lift the iron straight up.

Figure 11: A shiny, smooth, and concave cone means success

If the cooled and hardened solder has a spike, the iron tip temperature is not correct, or the flux is inactive. In this case, remove the solder, adjust the temperature, clean the tip and try again.

Do not solder all leads of the IC socket at once. Solder only one lead first and visually check that the socket is in contact with the PCB without a gap.

If the socket is not in contact with the board without a gap but is held in place by cooled solder, melt the solder with an iron to allow the socket to move and gently hold the socket down so that it is in close contact with the PCB surface (Figure 12). Once you are certain that there is no longer a gap, solder the remaining leads.

Figure 12: If the IC socket is not in close contact with the board, melt the solder and hold down the socket.

Soldering of Chip Components

This section describes the procedure for soldering chip components shown in Figure 13 to a PCB.

Figure 13: Examples of Chip Components: Commonly Used 1608-Size Resistors, Capacitor, and LED

Figure 14 shows the PCB before soldering.

Figure 14: Soldering of Chip Component: Mounting Pattern and Chip Component before Soldering

First, deposit a very small amount of solder on one pad (Figure 15). For chip components, large amounts of solder are not required.

Figure 15: Deposit small amount of solder on one pad.

Position the chip component with tweezers while holding the iron to the solder on the pad to melt it (Figure 16).

Figure 16: Melt solder with the iron. Position the chip component with tweezers.

Take away the iron and then tweezers (Figure 17).

Figure 17: After positioning, take away the soldering iron and then tweezers.

When the chip component is temporarily fixed to one pad, solder the chip to the other pad using the iron and solder wire as well (Figure 18). The result should look like Figure 19.

Figure 18: Hold the iron and solder wire to the other pad.

Figure 19: Finished depositing solder on the other pad.

Finally, revisit the first pad and add solder (Figure 20).

Figure 20: Add solder to the first pad.

Figure 21 shows the appropriate amount of solder for chip components. Ideally, the pad and chip end face should be well wetted to form a concave fillet.

Figure 21: Appropriate amount of solder for chip component:
Pad and chip end face should be well wetted to form a concave fillet.

Manufacturers use reflow equipment to solder chip components. Reflow allows a small amount of solder to adhere to the chip component, which is difficult by manual soldering.

When soldering chip components using an iron, the footprint of the component should be slightly larger to make soldering easier and more reliable. However, if the footprint is too large, solder will not be applied properly during reflow mounting. It is advisable to prepare different footprints for manual soldering and for mass production using reflow equipment.

Soldering of Surface-Mount ICs

Surface-mount ICs (Figure 22) are mounted in the same way as chip components. Figure 23 shows the pads before mounting the IC.

Figure 22: Appearance of Surface-Mount IC (8-pin SOC)

Figure 23: Soldering of Surface-Mount ICs：Pads for 8-pin SOC before Soldering

Deposit a small amount of solder on the pad at the top (Figure 24). The result should look like Figure 25.

Figure 24: Feed solder to pin 1.

Figure 25: Finished depositing solder on pin 1.

Hold an iron to pin 1 to melt it, position the IC for mounting (positioning) with tweezers (Figure 26) and take away the iron (Figure 27).

Figure 26: Melt pin 1, position the IC for mounting.

Figure 27: Take away the tweezers and iron from IC. IC is temporarily fixed.

Continue soldering the remaining pins (Figure 28).

Figure 28: Continue soldering the remaining pins.

Visually check from above (Figure 29) and from the side (Figure 30) that there is no bridging with adjacent pins.

Figure 29: Top View of Soldered IC

Figure 30: Side View of Soldered IC

Hands Are the Most Important Tools

The key to soldering is to use your hands well. Develop your soldering skills through practice. Also try various tools to assist your hands, such as vises, bulldog clips, and clothespins. With practice, you will be able to work without any aids (Figure 31).

Figure 31: Manipulate the wire, solder, and iron for pre-tinning.