Most companies are now using surface mount technology while moving toward ball grid arrays, chip scale packaging and even flip chip assembly. However, some companies still use through-hole technology. The use of through-hole technology is not necessarily related to cost or experience; it may simply be that the product does not require miniaturization. Many companies continue to use traditional through-hole components and will continue to use these parts on hybrid technology products. This article takes a look at some less common process issues. Hopefully, a year of traditional component assembly problems and their practical solutions will help provide insight into what can still go wrong in today's manufacturing.
Static electricity damages components. Static electricity is an objective natural phenomenon that occurs in many ways, such as contact, friction, current flow, etc. The basic process of its generation can be summarized as the formation of charge separation through the contact charge transfer dielectric layer. Static electricity on equipment or the human body can reach tens of thousands or even hundreds of thousands of volts, and often reaches hundreds to thousands of volts under normal operating conditions. The human body can carry thousands or even tens of thousands of volts of static electricity due to factors such as its own movements and contact, separation, friction or induction with other objects. Static electricity is the result of a local imbalance of positive and negative charges. It is a kind of electrical energy that is retained in objects and has the characteristics of high potential, low power, small current and short action time. The main measures for static electricity control include static electricity leakage and dissipation, static electricity neutralization, electrostatic shielding and grounding, humidification, etc. Component breakdown damage caused by electrostatic discharge is the most common and serious electrostatic hazard in the electronics industry. It is divided into hard breakdown and soft breakdown. Hard breakdown is a one-time cause of dielectric breakdown, burnout or permanent failure of components. Soft breakdown is a cause of device performance degradation or parameter index decline.
Anti-static loading boxes, component boxes, turnover boxes, turnover pallets, etc. must be used for the transfer and storage of static-sensitive components and printed circuit boards between processes during the production process. To prevent static electricity accumulation from causing harm. Static-sensitive components and printed circuit boards must be packaged as finished products in anti-static shielding bags, packaging bags, packaging boxes, strips, baskets, etc. to avoid electrostatic damage during transportation. During the production process of electronic products, components and finished components often come into contact with, separate from, equipment, tools, etc., and friction causes static electricity. Anti-static cushions, turnover carts, maintenance kits, tools, work chairs (stools), etc. must be used, and Discharge static electricity quickly through proper grounding. Frictional electrification and human body static electricity are two major sources of hazards in the electronics and microelectronics industries. However, the generation of static electricity is not the hazard. The hazard lies in the accumulation of static electricity and the resulting discharge of electrostatic charges, so they must be controlled.
Static-charged objects form an electrostatic field around them, which will produce mechanical effects, discharge effects and electrostatic induction effects. Due to the mechanical effect of static electricity, floating dust particles in the air will be adsorbed to electronic components such as silicon wafers, seriously affecting the quality of electronic products. Therefore, anti-static measures must be taken to purify the work space. The walls, ceilings and floors of the clean room should be made of anti-static, non-dust-generating materials, and a series of electrostatic protection measures should also be taken for operators, workpieces and equipment. In order to understand the electrostatic charging situation during the production process, determine the degree of influence of static electricity during the production process, and inspect the quality of electrostatic protective supplies and equipment, it is necessary to measure static electricity and related parameters. The measurement of static electricity mainly includes the measurement of electrostatic voltage, material resistance, grounding resistance, static off-life time, static electricity quantity, static eliminator discharge performance, cloth charge area density, etc. Electrostatic protection work is a systematic project. Omissions or mistakes in any link will lead to the failure of electrostatic protection work. Precautions must be taken at all times and everyone must take precautions.
We used optical photographs and scanning electron microscopy (, ) to see electrostatic breakdown on the surface of a silicon wafer. Electrostatic discharge, introduced to a pin, causes the component's working status to change, leading to system failure. Simulations of electrostatic discharge in the laboratory can also show failures occurring on the chip surface in real time.
Static electricity can be a problem and the solution is an effective control policy. Wrist straps are the most important initial defense. Dendrite Growth Dendrite occurs when an applied voltage is combined with moisture and the presence of some ionizable products. Voltage will always have to be on a circuit, but moisture content will depend on the application and environment. Ionizable materials can originate from the surface of the printed circuit board due to poor cleaning during assembly or during the blank manufacturing stage.
If investigating such defects, do not touch the board or component. Have the defect photographed and studied before all evidence of the cause of the failure is destroyed. Contamination can often come from the soldering process or the flux used. Another possibility is general handling dirt introduced during assembly. The most common cause of defects in industry comes from flux residue.
In the example above, the failure occurred after the component was reworked. This particular phone unit was refurbished by a third-party company using highly active flux, unlike the lower-active materials used during the original manufacturing. Solder Pad Cracking Shaped pads are typically used when components or wires must be installed as a second-stage assembly. Examples are heavy components, wire braiding, or components that cannot meet soldering requirements. In some cases, quality personnel were unaware of the cause of the breakage and assumed it was a corrosion issue.
A design trap, not a flaw. There are two cracks on the pads, but only one is needed to prevent soldering and generally prevents the direction of the soldering process. Solder Ball Solder balling is a problem for any engineer introducing no-clean technology. To help control the problem, he had to reduce the number of different circuit board suppliers his company used. By doing this, he will reduce the different solder mask types used on his board and help isolate the main problem solder mask.
Solder balls can be caused by many process issues during assembly, but if the solder mask does not allow the solder balls to stick, the problem is solved. If the solder mask type does not allow solder balls to stick to the surface, then this opens a process window for the engineer. The most common cause of solder balling is outgassing from the flux on the surface of the wave, where the solder pops out of the surface of the tin pot as the board is processed from the wave. Solder shorts between IC pins at the molten solder joints of the socket are not that common, but can occur. Generally a short circuit is the result of a process problem that is too high. This problem may arise from the wireless process and must be considered for future process assembly.
The use of tin/lead terminals on the pins and/or pins of the socket increases the possibility of short circuits. The parts are literally fused together. The problem gets worse if you change the tin/lead thickness on the contact surface. If we used all lead-free, there would be less fusible coating on the pins and sockets and the problem could be avoided. This problem can also be avoided by not preloading. Solder Joint Failure The reliability of a single-sided solder joint is determined by solder quantity, hole-to-lead ratio, and pad size. The above example shows a failed solder joint with a relatively small solder joint cross-section.
The hole to pin ratio in this example is large, resulting in a weak solder joint. As the distance from the pin to the edge of the hole increases, the thickness of the solder joint decreases in cross section. If any mechanical stress is applied to the solder joint, or if the solder joint is exposed to temperature cycling, the results will be similar to the example shown. Yes, you can add more solder, but that will only extend the life and not eliminate the problem. This type of failure can also occur due to improper handling of already fragile solder joints. Incomplete weld fillet An example of an incomplete weld fillet on a single panel. This defect occurs for many reasons. Incomplete solder fillets are caused by improper hole-to-lead ratios, steep conveyor angles, excessive peak temperatures, and contamination on the pad edges. The photo shows a clear example of improper hole to pin ratio, which makes mass soldering of this contact difficult to achieve. The design rule for pin to hole ratio is the pin size plus at least (). The holes with () can also obtain satisfactory solder joints during welding. An often forgotten issue is that as the pin-to-hole ratio increases, the size of the solder joint decreases, which is affecting the strength and reliability of the solder joint.
The example above also shows deburring on the copper pads. During drilling or punching, the copper on the board has tilted in some areas, making soldering difficult. If the rosin is applied to the edge of the pad from either the substrate or the joint between the substrate and the copper pad. (Shenzhen Jingkechuang Electronic Equipment Co., Ltd.)
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