The factory that assembles electronic products mainly includes two production lines: SMT surface assembly and DIP plug-in assembly. SMT is the process of attaching electronic components to a PCB circuit board through a device, heating them in a furnace (usually referred to as a reflow soldering furnace), and fixing the components to the PCB board through solder paste welding; And DIP has some large connectors that cannot be connected to the PCB board by devices, so it needs to be plugged into the PCB board through people or other automation devices.
In the production process of SMT and DIP, various factors can lead to quality issues in the product, such as solder joints. This not only leads to unstable performance of the product, but also cannot be detected by subsequent ICT and FT tests, leading to the flow of problematic products to the market, ultimately causing significant losses to the company’s brand and reputation. So how to avoid such problems, this article will carefully expand on science popularization for everyone.
Reasons for SMT false soldering
1. PCB pad design defect
In the design process of some PCBs, due to the small space, the vias can only be punched on the bonding pad, but the solder paste has fluidity, which may penetrate into the hole, resulting in the loss of solder paste in Reflow soldering. Therefore, when the pin is not enough tin, it will lead to faulty soldering.
2. Surface oxidation of solder pads
After the oxidized bonding pad is repainted with tin, the Reflow soldering will lead to faulty soldering. Therefore, when the bonding pad is oxidized, it needs to be dried first. If the oxidation is serious, it needs to be abandoned.
3. The reflow soldering temperature is too low or the high temperature zone time is not enough
After the placement is completed, the temperature is not enough when passing through the preheating zone and constant temperature zone of reflow soldering, resulting in some parts not yet experiencing hot melting and tin crawling after entering the high-temperature reflow zone, resulting in insufficient tin on the component pins and resulting in false soldering.
4. Insufficient printing quantity of solder paste
When brushing solder paste, the stencil may have a small opening and the pressure of the printing scraper is too high, which may lead to less solder paste printing and rapid volatilization of Reflow soldering solder paste, thus causing faulty soldering.
5. Pin device
High pin devices in SMT may experience deformation of the components, bending of the PCB board, or insufficient negative pressure of the SMT machine, resulting in uneven soldering and hot melting, leading to false soldering.
Reasons for DIP solder joint failure
1. PCB plugin hole design defect
The plug-in holes of the PCB have a tolerance of ± 0.075mm. The PCB packaging holes are larger than the pins of the physical device, causing the device to become loose, resulting in insufficient soldering and quality issues such as poor soldering or empty soldering.
2. Pad and hole oxidation
The PCB pad holes are unclean, oxidized, or contaminated with dirt, grease, sweat, etc., which can lead to poor solderability or even non solderability, leading to false soldering and empty soldering.
3. Quality factors of 3PB boards and devices
The solderability of the purchased PCB boards, components, and other components is not qualified, and strict acceptance tests have not been conducted. There are quality issues such as false soldering during assembly.
4. Expiration of 4PCB boards and devices
The purchased PCB boards and components have a long inventory period and are affected by the warehouse environment, such as temperature, humidity differences, or corrosive gases, resulting in false soldering and other phenomena during welding.
5. Wave soldering equipment factors
The excessively high temperature in the wave soldering furnace leads to accelerated oxidation of the solder material and the surface of the base metal, resulting in a decrease in surface adhesion to the liquid solder material. Moreover, the high temperature also corrodes the rough surface of the base metal, causing a decrease in capillary action and a decrease in diffusivity, leading to false soldering.
A Practical Tool for Solving the Problem of False Soldering
1. Solve the problem of SMT solder joints
Huaqiu DFM software has special analysis items for SMT patch assembly, such as standard size detection of various chip pads, BGA pad detection, and other patch pin pad abnormalities detection. The detection rules are set based on production processes, potential quality anomalies, etc., and can meet various quality issues related to solderability in SMT production.
2. Solve the problem of DIP solder joints
The solderability analysis of Huaqiu DFM software focuses on the analysis items of DIP plugin assembly, such as detecting the size of solder pad aperture, checking the number of pins in the plugin, and detecting various abnormalities in the plugin hole. The detection rules can be set according to the required production process, which can meet the quality issues of various weldability in DIP production.
Application scenarios of weldability tools
1. Coordinate file organization
When the coordinate files provided by the customer are relatively cluttered, SMT factories can use Huaqiu DFM software to organize the coordinate files. For example, if the components in the coordinate files are facing incorrectly and the top layer is at the bottom layer, you can change them to the correct top layer here. After organizing the coordinate files, export them and reuse them to avoid pasting incorrect components.
2. BOM error checking
When there are differences in the packaging of components used in BOM files and PCBs, SMT factories can use Huaqiu DFM software for BOM file error checking to avoid using purchased incorrect components and wasting costs.
3. Matching component library
When the components and pads do not match, or when the pads do not contain pins smaller than the pins, the SMT factory can use the matching component library function of Huaqiu DFM software to compare whether there are any abnormalities between the component pins and pads to avoid pasting the wrong components.
4. Parameter settings
SMT factories can define the feeding direction during SMT processing on the parameter setting page of Huaqiu DFM software. If the feeding direction is not reasonable, it can lead to poor welding.
5. SMT pricing
SMT factories can use Huaqiu DFM software to quickly and accurately quote and output quotations. The pricing items include SMD, DIP, empty label, welding area, number of solder joints, device types, etc., which can be quickly and transparently priced to avoid inaccurate quotes.
6. BOM file comparison
When SMT factories check BOM files, if there are multiple versions, they can use the BOM comparison function of Huaqiu DFM software. During the process of organizing BOM lists, it is easy to forget the modification points of different periods and versions. Using the BOM comparison function can avoid version errors and incorrect components being pasted.
7. Component Search
When SMT factories are reviewing engineering documents, due to the large number of components, it is not convenient to query the location of a certain component. At this time, they can use the component search tool of Huaqiu DFM software to search for components by tag number and accurately locate the location of the components.
8. Assembly drawings
Assembly drawings mainly express the working principle of machines or components, the connections and assembly relationships between various parts, and the structural shapes of main parts. When SMT factories place patches, assembly files can be exported using Huaqiu DFM software.
9. Assembly analysis inspection items
The SMT factory uses Huaqiu DFM software to inspect engineering documents, which can avoid abnormalities caused by engineering documents on the production line. There are 10 major and 234 detailed inspection rules for SMT weldability inspection items, which can fully solve the problem of weldability abnormalities caused by design documents.
10. Simulation diagram viewing
SMT factories can use the simulation diagram of Huaqiu DFM software to view engineering documents, because the simulation diagram can directly view the effect of pasted components, and can see the effect diagram of the finished board before production to avoid abnormalities during the board placement.
