1. How does SMT solder paste affect soldering quality?
The flux mass ratio and composition of solder paste flux components:
(1) Film-forming substances: 2%~5%, mainly rosin, and derivatives, synthetic materials, the most commonly used is water-white rosin.
(2) Activator: 0.05%~0.5%, the most commonly used activators include dicarboxylic acids, special carboxylic acids, and organic halide salts.
(3) Thixotropic agent: 0.2%~2%, increases viscosity and acts as a suspension. There are many such substances, preferably castor oil, hydrogenated castor oil, ethylene glycol mono butylene, and carboxymethyl cellulose.
(4) Solvent: 3%~7%, multi-component, with different boiling points.
(5) Others: surfactants, coupling agents.
Influence of solder paste flux composition on soldering quality:
Tin bead splash, flux splash, ball book array (BGA) void, bridging, and other poor SMT chip processing and welding have a great relationship with the composition of solder paste. The selection of solder paste should be selected according to the process characteristics of the printed circuit board assembly (PCBA). The proportion of solder powder has a great influence on improvingslump performance and viscosity. The higher the solder powder content, the smaller the slump. Therefore, the solder paste used for fine-pitch components should use 88%~92% more solder powder content of solder paste.
1. The activator determines the solderability or wettability of the solder paste. To achieve good soldering, there must be an appropriate activator in the solder paste, especially in the case of micro-pad soldering, if the activity is insufficient, it may cause grape ball phenomenon and ball-socket defects.
2. Film-forming substances affect the measurability of solder joints and the viscosity and viscosity of solder paste.
3. Flux is mainly used to dissolve activators, film-forming substances, thixotropic agents, etc. The flux in solder paste is generally composed of solvents with different boiling points. The purpose of using high boiling point solvents is to prevent solder and flux from splashing during reflow soldering.
4. Thixotropic agent is used to improving printing performance and process performance.
2. What are the factors that affect the efficiency of SMT production?
The placement cycle refers to the time it takes for the equipment placement head to start counting when the Feeder picks up the components, after image detection of the components, the cantilever moves to the corresponding position, the working axis places the components into the PCB board, and then returns to the Feeder feeding position. It is a placement cycle; the time used in the placement cycle is also the most basic parameter value affecting the speed of the placement machine. The placement cycle of high-speed cantilever placement machines for mounting resistance-capacitance components is generally within 1.0s. At present, SMT placement The cycle of the highest speed cantilever mounter in the chip processing industry is about 0.5s; the cycle of mounting large ICs, BGAs, connectors, and aluminum electrolytic capacitors is about 2s.
Factors affecting the placement cycle:
The synchronization rate of picking up components (that is, multiple linkage rods of a placement head rise and fall at the same time to pick up components).
PCB board size (the larger the PCB board, the larger the X/Y movement range of the placement head, and the longer the working time).
Component throwing rate (if the component image parameters are not set properly, equipment throwing and invalid X/Y actions will occur during the image recognition process of absorbing components).
The device sets the moving speed parameter value X/Y/Z/R.
3. How to effectively store and use solder paste in an SMT patch processing factory?
1. When the solder paste is not in use, it should be stored in the refrigerator, and its storage temperature must be within the range of 3~7°C. Please note that the solder paste cannot be frozen below 0°C.
2. There should be a dedicated thermometer in the refrigerator to detect the stored temperature every 12 hours and make a record. The thermometer needs to be checked regularly to prevent failure, and relevant records should be made.
3. When purchasing solder paste, it is necessary to paste the purchase date to distinguish different batches. According to the SMT chip processing order, it is necessary to control the use cycle of solder paste, and the inventory is generally controlled within 30 days.
4. Solder paste storage should be stored separately according to different types, batch numbers, and different manufacturers. After purchasing solder paste, it should be stored in a refrigerator, and the principle of first-in, first-out should be followed.
4. What are the reasons for cold welding in PCBA processing
1. The reflow temperature is too low or the residence time at the reflow soldering temperature is too short, resulting in insufficient heat during reflow and incomplete melting of the metal powder.
2. In the cooling stage, the strong cooling air, or the movement of the uneven conveyor belt disturbs the solder joints, and presents uneven shapes on the surface of the solder joints, especially at a temperature slightly lower than the melting point, when the solder is very soft.
3. Surface contamination on and around pads or leads can inhibit flux capability, resulting in incomplete reflow. Sometimes unmelted solder powder can be observed on the surface of the solder joint. At the same time, insufficient flux capacity will also result in incomplete removal of metal oxides and subsequent incomplete condensation.
4. The quality of solder metal powder is not good; most of them are formed by the encapsulation of highly oxidized powder particles.
5. How to Clean PCB Assembly in the Safest and Most Efficient Way
Cleaning PCB assemblies should use the most appropriate cleaner and cleaning solvent, which depends on the board requirements. Here, different PCB cleaning ways and their pros and cons are illustrated.
1. Ultrasonic PCB Cleaning
An ultrasonic PCB cleaner cleans bare PCBs quickly without cleaning solvent, and this is the most economical PCB cleaning method. Besides, this cleaning method doesn't restrict the PCB size or quantity. However, it can't clean PCB assembly because ultrasonic can harm electronic components and the assembly. It also can't clean aerospace/defense PCB because the ultrasonic can affect the board's electrical precision.
2. Full Automatic On-Line PCBA Cleaning
The full automatic on-line PCBA cleaner is appropriate to clean large volumes of PCB assembly. Both the PCB and PCBA can be cleaned, and it won't affect the boards' precision. The PCBAs pass different solvent-filled cavities to complete the processes of chemical water-based cleaning, water-based rinsing, drying, and so on. This PCBA cleaning method requires the solvent to be compatible with the components, PCB surface, solder mask, etc. And we also have to pay attention to the special components in case that they can't be washed. Aerospace and medical-grade PCB can be cleaned in this way.
3. Half Automatic PCBA Cleaning
Unlike the online PCBA cleaner, the half-automatic cleaner can be transported manually at any place of the assembly line, and it has only one cavity. Though its cleaning processes are the same as the online PCBA cleaning, all the processes happen in the same cavity. The PCBAs need to be fixed by a fixture or placed in a basket, and their quantity is limited.
4. Manual PCBA Cleaning
The manual PCBA cleaner is appropriate for small-batch PCBA that requires the MPC cleaning solvent. The PCBA completes the chemical water-based cleaning in a constant temperature bath.
We choose the most appropriate PCBA cleaning method depending on PCBA requirements.