Crafting the Perfect Manual Weld: Process Specifications

1. Purpose

To standardize manual welding operations in the production of processed plates and ensure product quality.

2. Scope

This general process specification is applicable to guide all external cooperation manufacturers and EMS factories producing PCBA-made boards for Emerson Network Power.

3. Application Standards

IPC-7711 Rework of Electronic Assemblies

IPC-7721 Repair and Modification of Printed Boards and Electronic Assemblies

4. Specifications

4.1 Tools and Requirements for Manual Welding

4.1.1 Soldering Irons

4.1.1.1 The soldering iron used in manual welding must have an anti-static grounding wire, and the grounding wire must be reliably grounded during welding. For lead-free welding, it is recommended to use a high-frequency eddy current heating principle soldering iron.

4.1.1.2 The insulation resistance of the soldering iron should be greater than 10MΩ, and the insulation layer of the power cord should not be damaged.

4.1.1.3 Use a multimeter in resistance mode, with the probe touching the soldering iron head and the ground terminal of the power plug. The stable displayed value of the ground resistance should be less than 3Ω; otherwise, the grounding is poor.

4.1.1.4 The soldering iron head should be free from defects such as oxidation, burns, or deformation.

4.1.2 Soldering Iron Holder

4.1.2.1 After the soldering iron is placed in the holder, it should be stable without any tendency to droop, and the guard ring should be able to cover all the heating parts of the soldering iron.

4.1.2.2 The cleaning sponge on the holder must be moistened with an appropriate amount of water to keep it wet but not drippy. This will help to achieve the best cleaning effect on the soldering iron head. If a non-moistened cleaning sponge is used, the soldering iron head may be damaged, resulting in no tin-plating. It is recommended to use pure water to moisten the sponge.

4.1.3 Tweezers: The port should close properly, and the tip of the tweezers should not be twisted or broken.

4.1.4 Anti-Static Wristband: It should pass the test, the wristband should be moderately tight, and the metal plate should fit well with the skin of the wrist. The grounding wire connection should be reliable.

4.2 Auxiliary Materials and Requirements for Manual Welding

Solder wire and flux for manual welding should be selected according to the designated specifications in DMBM0.054.272G “Selection and Use Specification of Main Auxiliary Materials for Single Board Production”.

4.3 Preparation for Manual Welding

4.3.1 If welding ESD devices such as manufactured plates or MOS devices, it is necessary to confirm the grounding of the soldering iron, and the operator should wear an anti-static wristband and have good grounding.

4.3.2 Check whether the soldering iron is heating normally and whether there is oxidation or dirt on the soldering iron head. The oxide on the copper soldering iron head can be polished off with fine sandpaper or a fine file.

Long-life soldering iron heads are not allowed to be filed; dirt can be wiped off on a moistened sponge. Before welding, a layer of bright solder should be applied to the soldering iron head.

If there is black oxide on the soldering iron head, it may not tin-plate, and it must be cleaned immediately. When cleaning, first adjust the temperature of the soldering iron head to about 250°C, then clean the soldering iron head with a cleaning sponge and then tin-plate. Repeat the action until the oxide is removed.

4.3.3 Check whether the temperature of the soldering iron head meets the requirements of the components to be welded. Temperature testing must be carried out every time the soldering iron is turned on and the temperature is adjusted, and records must be kept.

4.3.4 Check the leakage voltage of the soldering iron. Use a multimeter in AC mode to test the voltage between the soldering iron head and the ground wire, and record it. The requirement is less than 5V; otherwise, it cannot be used.

4.3.5 Principles for selecting soldering iron heads:

The size of the soldering iron head is directly related to the heat capacity. The larger the soldering iron head, the greater the relative heat capacity, and the smaller the soldering iron head, the smaller the heat capacity.

When continuous welding, the larger the soldering iron head, the less the temperature drop.

In addition, because the heat capacity of the large soldering iron head is high, it can use a relatively low temperature during welding, and the soldering iron head is not easy to oxidize, increasing its lifespan.

Short and thick soldering iron heads conduct heat longer and faster than long and thin soldering iron heads and are more durable. Flat and blunt soldering iron heads transmit more heat than sharp soldering iron heads.

Generally, the size of the soldering iron head should not affect adjacent components.

Choosing a geometric size that can fully contact with the solder joint can improve welding efficiency.

The geometric shape of the soldering iron head is crucial for excellent heat transfer.

Choose the appropriate shape and size of the soldering iron head to maintain the maximum contact area with the solder joint/solder pad to achieve the best heat transfer effect.

Therefore, the largest and lowest-temperature soldering iron head should be selected as much as possible, as shown in the figure below:

Here are the characteristics and application ranges of commonly used various shapes of soldering iron tips listed below.

4.3.5.1 I/LI Type

Characteristics: The tip of the soldering iron is delicate and fine.

Application Range: Suitable for precise welding or situations where space is limited. It can also be used to correct tin joints generated during the welding of chips.

4.3.5.2 B Type (Conical)

Characteristics: The B-type soldering iron tip is non-directional, and the entire front end of the soldering iron tip can be used for welding.

Application Range: Suitable for general welding. Regardless of the size of the solder joint, a B-type soldering iron tip can be used.

4.3.5.3 D Type (Chisel)

Characteristics: The chisel part is used for welding.

Application Range: Suitable for welding that requires a larger amount of tin, such as welding in environments with large welding areas, coarse terminals, and large solder pads.

4.3.5.4 C Type (Slanted Cylinder)

Characteristics: The sloping part of the front end of the soldering iron tip is used for welding, which is suitable for welding that requires a larger amount of tin.

Application Range: The application range of the C-type soldering iron tip is similar to that of the D-type soldering iron tip. It is suitable for welding in situations such as large welding areas, coarse device pins, and large solder pads.

The 0.8C and 1C type soldering iron tips are very fine and suitable for welding small components or correcting tin joints and solder columns generated during surface welding. If only a small amount of soldering is required, the CF-type soldering iron tip with tin plating only on the slope is more suitable.

The 2C and 3C type soldering iron tips are suitable for welding resistors, diodes, and components with larger pin spacing such as SOP and QFP. The 4C type is suitable for welding large device pins and large-area welding situations that require more heat.

4.3.5.5 K Type

Characteristics: The blade-shaped part is used for welding, and both vertical and drag soldering can be performed. It is a versatile soldering iron tip.

Application Range: Suitable for welding SOJ, PLCC, SOP, QFP devices, devices with large copper foils, connectors, etc., as well as correcting tin joints.

4.3.5.6 H Type

Characteristics: The tin plating layer is at the bottom of the soldering iron tip.

Application Range: Suitable for drag soldering with larger pin spacing of SOP and QFP devices.

The selection of soldering iron head models can refer to the following table:

4.4 Requirements for manual soldering using leaded process

4.4.1 General requirements for manual soldering using leaded process:

The temperature of the soldering iron is generally controlled between 280~360℃, with a default setting of 330℃, and the soldering time is less than 3 seconds.

During soldering, the soldering iron head should simultaneously touch the solder pad and the component pin.

After heating, the solder wire should be fed for soldering.

Do not put the solder wire directly on the soldering iron head, but place it between the soldering iron head and the solder joint to be soldered, as shown in the figure below:

The soldering iron head should be dipped in tin to achieve the best heat transfer effect. The special welding requirements for some components are described below, and the special welding requirements for other components should be referred to the specific single-board process instructions.

4.4.2 When welding relays, use a 40W constant temperature soldering iron with a temperature control between 280~300℃ and a time control between 2~3 seconds.

When the solder joint is connected to the large copper foil and the above temperature cannot be used for welding, the soldering iron temperature can be increased to 330℃. Note that relays that have undergone severe vibration or dropping cannot be used.

4.4.3 When welding power devices packaged in TO-220, TO-247, TO-264, etc., use a 60W (or 100W) constant temperature soldering iron with a temperature control between 320~340℃ and a time control between 2~3 seconds.

When the solder joint is connected to the large copper foil and the above temperature cannot be used for welding, the soldering iron temperature can be increased to 360℃.

4.4.4 When welding cables and pins, use a 60W (or 100W) constant temperature soldering iron with a temperature control between 350~360℃ and a time control between 2~3 seconds.

When the solder joint is connected to the large copper foil and the above temperature cannot be used for welding, the soldering iron temperature can be increased to 390℃.

4.4.5 Requirements for SMD soldering and rework

4.4.5.1 Soldering Iron Requirements

Use HAKKO 936 60W soldering iron.

4.4.5.2 When removing defective components, use the HAKKO-3C soldering iron head;

4.4.5.2 Soldering iron head used during soldering:

Chip components:

Components below (including) size 1210: use HAKKO-1C soldering iron head;

Others: Use HAKKO-3C soldering iron head;

Tantalum capacitors:

Type A and B: use HAKKO-1C soldering iron head;

Type C and D: use HAKKO-3C soldering iron head;

4.4.5.3 Solder wire requirements

Use KSETER 245 solder wire with a diameter of Ф0.5mm,

Solder wire flux content: 1.1% (W/W%)

4.4.5.4 Process parameter requirements:

The temperature of the soldering iron during welding is: 320±10℃;

Soldering time: 1~3 seconds per solder joint;

The temperature of the soldering iron when removing components: 310~350℃.

4.4.5.5 Operation requirements:

4.4.5.5.1 Removal of defective components:

Heat the component with a HAKKO-3C soldering iron head, apply solder wire to melt the solder joints on both ends of the component, and remove the component with tweezers.

4.4.5.5.2 Processing of chip components after removal:

Ceramic chip components cannot be reused after removal. Ceramic chip components mainly include ceramic chip resistors (most of which are ceramic, and a few are plastic-packaged), ceramic chip capacitors (most of which are ceramic, and a few are plastic-packaged, such as tantalum capacitors), ceramic chip inductors (most of which are wire-wound, and a few are ceramic).

After being removed from the single board (using an electric soldering iron), they cannot be used again.

4.4.5.5.3 Welding of new components:

Use tweezers to pick up the component and place it in the position to be welded. It is absolutely not allowed to use the heating part of the electric soldering iron (especially the soldering iron head) to stick the chip component as a way of moving the chip component.

Use the corresponding soldering iron head according to the requirements of 4.4.5.2 for different components, and weld both soldering surfaces of the component under the requirements of 4.4.5.4.

During the welding process, the heated part (especially the soldering iron head) of the electric soldering iron must not touch any part of the chip component other than the non-welding surface of the chip component, and can only be in contact with the welding surface.

4.5 Lead-free manual soldering requirements

4.5.1 General requirements for lead-free manual soldering:

Due to the higher melting point (217℃) of the solder wire used in lead-free manual soldering than that (183℃) of the solder wire used in leaded process, higher requirements are put forward for the reflow speed of the soldering iron.

In order to meet the requirements of lead-free manual soldering, it is recommended to use an electric soldering iron that adopts high-frequency eddy current heating principle with faster reflow speed.

The temperature setting principle of the electric soldering iron is to heat the solder joint with the soldering iron head, so that the temperature of the solder joint is 30℃ higher than the melting point of the solder, and maintain it for 2-3 seconds, so as to form a strong and reliable solder joint.

The temperature of the electric soldering iron is generally controlled between 300-360℃, default setting at 330℃, and the welding time is less than 5 seconds.

When welding, the soldering iron head should contact both the pad and the pins of the component, and then feed the solder wire after heating.

Do not put the solder wire directly on the soldering iron head, but put it between the soldering iron head and the solder joint to be welded. The soldering iron head should be dipped in tin to achieve the best heat transfer effect.

See below for the welding requirements of different types of solder joints, and refer to specific single-board process instructions for special welding requirements of other components.

4.5.2 For THT devices with pin cross-sectional area ≤3mm2 and no connection to large copper foil, control the temperature between 320-340℃ and the time between 3-5 seconds; when the solder joint is connected to the large copper foil and the above temperature cannot be used for welding, the soldering iron temperature can be increased to 360℃ and time controlled between 5-8 seconds.

4.5.3 For THT devices with pin cross-sectional area between 3mm2 and 12mm2 and no connection to large copper foil, control the temperature between 330-350℃ and the time between 3-5 seconds; when the solder joint is connected to the large copper foil and the above temperature cannot be used for welding, the soldering iron temperature can be increased to 380℃ and time controlled between 5-8 seconds.

4.5.4 For THT devices with pin cross-sectional area ≥12mm2 and no connection to large copper foil, control the temperature between 340-360℃ and the time between 3-5 seconds; when the solder joint is connected to the large copper foil and the above temperature cannot be used for welding, the soldering iron temperature can be increased to 380℃ and time controlled between 8-15 seconds.

4.5.5 Requirements for SMD soldering and rework

4.5.5.1 Soldering Iron Requirements

It is recommended to use an electric soldering iron that adopts high-frequency eddy current heating principle.

4.5.5.2 When removing defective components, use the 3C soldering iron head;

4.5.5.3 Soldering iron head used during soldering:

Chip components:

For components with sizes below 1210 (including 1210): use the 1C soldering iron head.

Others: use the 3C soldering iron head.

Tantalum capacitors:

Type A/B: use the 1C soldering iron head;

Type C/D: use the 3C soldering iron head.

4.5.5.4 Process parameter requirements:

Soldering iron temperature during welding: 320±10℃

Welding time: 1-3 seconds per solder joint

Soldering iron temperature when removing components: 310~350℃

4.5.5.5 Operation requirements:

4.5.5.5.1 Removal of defective components:

Heat the component with a 3C soldering iron head, apply solder wire to melt the solder joints on both soldering surfaces of the component, and then remove the component with tweezers.

4.5.5.5.2 Processing of chip components after removal:

Ceramic chip components cannot be reused after removal.

Ceramic chip components mainly include ceramic chip resistors (most of which are ceramic, and a few are plastic-packaged), ceramic chip capacitors (most of which are ceramic, and a few are plastic-packaged, such as tantalum capacitors), ceramic chip inductors (most of which are wire-wound, and a few are ceramic).

After being removed from the single board (using an electric soldering iron), they cannot be used again.

4.5.5.5.3 Welding of new components:

Use tweezers to pick up the component and place it in the position to be welded. It is absolutely not allowed to use the heating part of the electric soldering iron (especially the soldering iron head) to stick the chip component as a way of moving the chip component.

Use the corresponding soldering iron head according to the requirements of 4.5.5.3 for different components, and weld both soldering surfaces of the component under the requirements of 4.5.5.4.

During the welding process, the heated part (especially the soldering iron head) of the electric soldering iron must not touch any part of the chip component other than the non-welding surface of the chip component, and can only be in contact with the welding surface.