Analysis and improvement of welding defects in appearance inspection standard of electronic components

Date：2022-08-08 16:53:02Views：1041

Any product will produce a small number of poor appearance more or less during production, and electronic components are no exception. Welding components with electric soldering iron is a basic assembly process, which plays a key role in ensuring the quality of electronic products. The components in various electronic products have their own characteristics, and the inspection contents shall be determined according to the specific requirements of each component. In order to help you have a deeper understanding, the following contents are organized by Chuangxin testing network for your reference.

Requirements for standard welding points:

1. Reliable electrical connection

2. Sufficient mechanical strength

3. Clean and tidy appearance

Analysis of solder joint defects of electronic components

(1) Bad terms

Short circuit:Two or more points of the same line are not connected and are in a conducting state.

Peeling:The copper foil of the line is separated from the bottom plate of the line due to excessive heat or external force.

Less tin:The pad is not complete, or the solder joint is not full.

False welding:The solder surface is full and shiny in wave shape, but it is not melted with the circuit copper foil or completely melted on the circuit copper foil.

Desoldering:The component foot is separated from the solder joint.

Faulty welding:The solder is separated from the element at the lead part.

Fillet welding:The loss of flux due to excessive heating will lead to the phenomenon of solder sharpening.

Pull point:The solder joint is not smooth and appears dull due to the loss of flux.

Element foot length:The length of the element foot exposed to the plate bottom exceeds 1.5-2.0mm.

Blind spot:The component pin is not inserted out of the board surface.

(2) Causes, manifestations and improvement measures of adverse phenomena

1. Heating time problem

(1) Insufficient heating time: the solder can not fully infiltrate the weldment to form rosin slag and cause false welding.

(2) If the heating time is too long (excessive heating), in addition to possible damage to components, there are also the following hazards and external characteristics.

A. The appearance of the solder joint becomes poor. If excessive heating is continued after the solder has soaked the weldment, the flux will be volatilized completely, resulting in overheating of the molten solder. When the soldering iron leaves, it is easy to pull out the tin tip, and at the same time, the surface of the solder joint is white, rough particles appear and lose luster.

B. High temperature causes decomposition and carbonization of rosin flux. Rosin generally begins to decompose at 210 ° C, which not only loses the role of flux, but also causes slag inclusion in the solder joint to form defects. If the rosin is found blackened during welding, it must be caused by too long heating time.

C. Excessive heat will damage the adhesive layer of copper foil on the printed board, resulting in peeling of the copper foil pad. Therefore, in the proper heating time, the key to welding is to accurately grasp the heating temperature.

(3) Causes and hidden dangers of bad solder joints

1. Rosin residue:A thin film of flux is formed.

Hidden danger: poor electrical contact.

Cause analysis: the power of the soldering iron is insufficient, the welding time is short, and the lead or terminal is not clean.

2. Faulty welding:The surface is rough and without luster.

Hidden danger: reduce the mechanical strength of the welding point and reduce the product life.

Cause analysis: before the solder solidifies, the solder joint contacted by other things is heated excessively and the number of repeated soldering is too many

3. Crack welding:The welding point is loose, and the welding point has a gap. The welding point will move when the wire is pulled.

Hidden danger: poor electrical contact.

Cause analysis: before the soldering tin is cured, the solder joints contacted by other things are heated too much or not enough, and the leads or terminals are not clean.

4. Multi tin:Too much solder flows out of the solder joint and is wrapped into a ball with a wetting angle greater than 90 degrees. Hidden danger: it may affect the appearance of the solder joint, and there may be quality hidden danger, for example, there may be holes inside the solder joint.

Cause analysis: too much solder and too long heating time.

5. Pull point:The surface of the solder joint is protruding like a horn.

Hidden danger: it is easy to cause line short circuit.

Cause analysis: improper evacuation method and long heating time of soldering iron.

6. Less tin:The amount of solder is too small, and the wetting angle is less than 15 degrees.

Hidden danger: reduce the mechanical strength of the welding joint.

Cause analysis: the lead or terminal is not clean, the pre hung solder is insufficient, and the welding time is too short.

7. Improper handling of leads:The solder joint is rough, scorched, the lead is immersed, and the core wire is exposed too much.

Hidden danger: poor electrical contact, easy to cause short circuit.

Cause analysis: poor insulation caused by accumulation of dust or debris, the heating time is too long, and the lead wire is poorly bound.

8. The insulation part of the terminal is burnt:The welding metal is overheated, causing the insulation part to burn.

Hidden danger: it is easy to cause short circuit.

Cause analysis: the solder and flux are scattered when the heating time is too long.

(4) Improvement of defective solder joints

1. Sharpen

Cause: the heating time is too long, the amount of flux used is too small, and the angle of dragging tin is incorrect.

Countermeasures: the welding time shall be controlled at about 3 seconds, the amount of flux used shall be increased, and the angle of dragging tin shall be 45 degrees.

2. Voids and pinholes

Cause: the lead wire of the component is not pre hung with tin, which causes voids around the lead wire, and the PCB board is affected by moisture

Countermeasures: properly extend the welding time, conduct tin pre coating treatment on the oxidized pins, and dry the damp PCB.

3. Polytin

Causes: the temperature is too high, the amount of solder used is too large, and the solder angle is not well mastered.

Countermeasures: use proper soldering iron, manage the temperature of the soldering iron, reduce the amount of solder properly, and the angle is 45 degrees.

4. Cold welding

Cause: after welding, the solder is shaken or vibrated before it is cooled and solidified, causing the solder to sag or produce stress lines

Countermeasures: after the solder joints are completely cooled, the PCB board can flow into the next station.

5. Poor wetting

Cause: the pad or pin is oxidized, the welding time is too short, and the tin dragging speed is too fast.

Countermeasures: conduct tin pre coating treatment on oxidized pads or pins, appropriately slow down the welding speed, and control the welding time to 3 seconds.

6. Continuous welding

Cause: other lines are short circuited due to poor solder fluidity.

Countermeasures: proper flux shall be used during welding, the welding time shall be controlled at about 3 seconds, and the welding temperature shall be appropriately increased.

The above is related to the appearance of electronic components compiled by the Chuangxin testing team. I hope it can help you. Chuangxin testing is a professional testing institution for electronic components. Currently, it mainly provides testing services for integrated circuits such as capacitors, resistors, connectors, MCU, CPLD, FPGA and DSP. Specializing in functional testing of electronic components, incoming appearance testing of electronic components, anatomical testing of electronic components, acetone testing, X-ray scanning testing of electronic components, and RoHS component analysis testing. Welcome to call, we will serve you wholeheartedly!