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EnglishPCBA through-hole device rework process, for many operators, is nothing more than using a tin furnace or other heating tools to remove the device to be repaired and install new devices and soldering. Very few people from the PTH rework quality reliability aspects To conduct in-depth research and develop a controllable and efficient PCBA substrate rework and soldering solution.
However, both the product itself and the standpoint of the customer must meet the requirements for quality and reliability of the PCBA substrate repair. The following mainly takes the lead-free PCBA through-hole device repair process and PCBA rework technology as an example, and analyzes the problems encountered in customer audit and actual maintenance, mainly from the following perspectives:
1. Preheating:
In order to prevent direct thermal shock to the PCBA substrate, reduce PCBA deformation, and consider the ability to rework the PCBA rework device in a shorter period of time (to prevent the immersion time from being too long and cause the via to shrink), preheating is required. .
2. Dip time:
After the lead-free pad is heated to the tin-melting temperature, the dissolution rate of the PCB pad exposed to tin is proportional to the temperature and time, that is, the higher the temperature, the longer the time, and the larger the pad dissolution area and depth. According to the IPC610F standard, when the pad size is less than 75% of the original area, the soldering reliability requirement cannot be achieved. In the repair of PCBA through-hole devices, the reliability of the copper hole wall thickness less than 13um will not be guaranteed. Therefore, in order to ensure that the pad dissolution area can be made smaller when using the PTH rework equipment to operate the PCBA substrate rework process, it is necessary to minimize the immersion tin (contact tin) time at the same temperature.
3. Temperature parameter setting during welding:
Temperature control is a very important part of the PTH rework station in the rework process. We need to master some techniques in the PCBA substrate rework process. According to the DOE test, if the lead-free solder is tin-silver-copper alloy (96.5%Sn, 3%Ag, 0.5%Cu) rework, tin temperature should be set at 265 degrees Celsius (within plus or minus 10 degrees), preheating temperature BOTTOM surface should not exceed 140 degrees Celsius, TOP surface should not exceed 120 degrees, otherwise it may be more resistant to temperature on PCBA Low device effects.
4. Through hole to eat tin:
In the PCBA through-hole device rework, in terms of the amount of tin in the PTH through-hole, according to the requirements of IPC610F, the amount of tin in the through-hole reaches 3/4 of the height of the through-hole. In order to prevent the shortage of tin, IBM and other customers recommend the PCBA board to be repaired. In the soldering process, the PTH rework equipment can control the height of the tin wave to form an upward impact force but can not overflow the tin. Generally, the tin wave is further dropped for 1 second after immersion for 3-5 seconds, and then the tin soldering is performed.
5. PTH through hole rework process standardization and control:
In the PCBA rework operation example, when the relevant rework parameters are set, in addition to writing them to the operation execution control file (such as the work instruction), it is better to automate in order to make the operation better. For example, an automated rework device that can save relevant rework parameters and can be managed with the program name is a widely-referred safety rework program.
example:
The PTH rework equipment that finally passed the customer quality audit is the VT-128 PTH rework station of Haotai Technology Co., Ltd.:
The following is a temperature profile for pre-repair debugging of a large server motherboard DIMM device for the customer's requirements:
(Note: The DIMM slot connector is the most pinned device on the motherboard, and it is the most difficult device to repair in practice, so the customer chooses whether the device can be repaired for evaluation reference).
Temperature graph description:
The temperature curve is divided into preheating-welding zone, wherein the welding time zone includes three parts of disassembly-loading-welding, each immersion tin and fallback is 1 cycle, the first 3 cycles are the time of dismantling the old device, and the last 3 The cycle is the time to install and solder new devices, and the total immersion tin time is controlled within 30 seconds.
Temperature measurement point description:
TOP JOINT and BOT JOINT are the upper and lower solder joint signal points of the PCB through-hole, and TOP JOINT1 and BOT JOINT1 are the grounding points of the upper and lower solder joints of the PCB through-hole. BODY is the device.
The results of the slicing after the DIMM device is soldered are as follows:
The final result confirms that the VT-128 PTH through-hole device rework equipment can fully meet the customer's rework quality and reliability requirements, and is recognized by customers and passed quality audit.