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through-hole rework of thermal dissipating assemblies: step-by-step instructions are given for a new method of reworking expensive through-hole heat sink assemblies.

by:Mingfa Tech     2019-11-12
Because it\'s familiar through
Hole technology is not as glamorous or exciting as the evolving surface
Installation technology.
In addition to reducing the size of the Assembly, the realization of the surface
Mount technology transfers resources to new components and processes.
However, when passing-
Rework holes are required and the method must maintain the initial integrity of the Assembly.
Especially the big heat-
Through-dissipate components
Hole parts are still an important rework issue.
Using existing manual rework methods, the debris buckets, masks and pads of these expensive components can easily be damaged.
Therefore, a new rework method was developed to combine the temperature, time and movement of the welding module with the computer control of the pre-heater.
Before pre-decomposition, the hot gas system is used to remove solder from the barrel (Figure 1).
In the new method, it takes four main steps to successfully pass the following steps
Hole repair: preheating, dismantling, plug-in, pre-rotation. [
Figure 1 slightly]
The key element of warming up this step is high
Provide an overall assembled heated wattage system within a reasonable time frame.
The board is loaded into the electric carrier system and is automatically placed in the preloader to set the temperature.
It is then automatically transferred from the pre-heater to the return module immediately.
Use a separate preheat oven or system manually or in bulk-
Type method, but must ensure safety when transferring the heating assembly.
In addition, the loss of heat due to treatment must be considered.
The assembly must be preheated for the following reasons: * to minimize the heat absorption of the entire assembly during flow.
Overheating may damage the mask, or cause the board to strip or change color.
Preheating also reduces the power and capacity of the required system.
* Reduce the thermal gradient to minimize local PCB warping.
* Reduce the time of process or local heating, thereby minimizing overheating of the components.
Clues may be separated from clues
Plastic case.
The leads will remain in the plate bucket, making it difficult to disassemble or overheat the Assembly when it is finally disassembled.
* Establish the same starting point for the return process.
* Provides uniformity of solder joint temperature by minimizing open solder joints.
* In order to alleviate the board warping caused by internal humidityfield oroff-line storage.
The relationship between the welding wave and the circuit board must be horizontal.
Component removal key elements in this step include: * high quality hot media such as 2,500 W, 35 lb.
Capacity welding * process control heating, time and temperature fixing * selective heating/welding contact to Assembly only * plate positioning level and accurate to welding wave;
Powerful carrier platforms and computers
Control panel positioning.
The plate is precisely positioned on a confined welding wave and its shape matches the lead pattern of the Assembly immediately after preheating (Figure 2).
Electric z
The speed and height of the Axis control assembly (leads)
Welding wave.
Low temperature welding flows at the bottom of the board for a few seconds while transmitting to all Assembly leads. [
Figure 2:Heat (
Temperature and time)
Components must be limited by damage to protective masks, assemblies, barrels and plate composites.
When all joints are melted (timed duration)
, The component is lifted from the board.
However, be careful not to remove the assembly before the largest radiator joint melts.
If not, the lead sand bucket may be damaged.
The large thermal mass of the system provides a uniform low temperature throughout the process.
By contrast, high
Temperature vacuum welding tools or manual Wick will damage the pads and masks due to excessive overheating at the tip.
It is easy to damage the circuit board by increasing the temperature in order to overcome the heat dissipation of the Assembly.
Due to excessive pressure, measuring the exact dwell time of the pads, tip positioning, and scraping of the pads and masks prevents the use of these manual methods.
There are several advantages to using welding as a hot medium.
A curved lead with a heating tip is required.
There is no re-heating of the partially welded joints, thus eliminating paddelamination.
The damage occurred mainly at this time as the operator was unable to determine which joints had been successfully de-welded.
The operator must then re-heat the joint without welding as a heat transfer medium.
In many cases
Lead connectors, hundreds of joints may have to be re-heated, which greatly increases the likelihood of damage.
With the new method, the average removal return time is 10 seconds.
The component has less heat applied-
At lower temperatures and in less time-
And fewer operator requirements.
The key elements in the component insert into this step include: * high-capacity warm-up, as described in the previous section * high-capacity non-
Contact heating to minimize heat dissipation and tip wear of the assembly * high-capacity vacuum flow and fast and complete welding removal Force * provide minimum maintenance for a sustained and long termterm usage.
After removing the part, the barrel must be completely cleaned in order to insert the part (Figure 3).
This part of the process is critical because when welded in a huge thermal component, solder must be heated and removed quickly.
For the same reason, the Wick or vacuum welding tool cannot be used.
Although it may be easy to see the liner damage, the mask damage may not be obvious. [
Figure 3 slightly]
Two methods or combinations can be used for component insertion: Hot/vacuum or low pressure air.
Method 1 the hot gas module provides the overall bottom heat for the circuit board (
Benefits of providing warm-up)
At the same time, a plane assembly platform is established.
The hot gas at controlled temperature and flow rate is directed to the residual solder on the PCB pad.
Heat is delivered to multiple barrels to ensure a gradual increase in temperature
To achieve the minimum thermal shock of melting welding.
The high vacuum flow system simultaneously removes excess molten solder to the collection chamber.
The hole is completely clean and allows for full insertion of the replacement part, especially when the position label must be fully in place.
The fixed position of the process and the clear stereo microscope observation eliminate the fine operational flexibility required by conventional methods.
The composite vacuum suction head ensures that there is no grinding or grounding metal contact with the assembly (Figure 4). [
Figure 4 slightly]
Method 2 after the assembly is removed, the air-
The cleaning cover is reduced relative to the plate surface. Low-
Apply the pressure air to the lead pattern, forcing the molten solder to flow out of the hole.
Bucket method May 1 (ground pin)
No cleaning.
However, some customers do not allow pressure air to come into contact with their components, so they cannot use this method.
The breakdown of key elements in this step includes: * high quality thermal media such as 2,500 W, 35 lb.
Capacity welding * process control heating, time and temperature fixing * selective heating/welding contact to Assembly only * plate positioning level and accurate to welding wave;
Powerful carrier platforms and computers
Control Board positioning * Control z
Eliminate the axis speed of the bridge.
Rinse the parts manually or automatically through the machine.
Use the same system as disassembly to load the plate into the motor carrier.
In order to reduce the sagging of the board, it may need to be fixed.
The board is placed on the pre-heater and then on the old module.
The plate is reduced to the welding wave (Figure 5). Lead-to-solder-
The computer controls the entry speed, duration, and exit speed of the wave.
A slow, uniform return welding speed is critical for the correct tin stripping to provide repeat successful welding.
The board returns to the loading and unloading position. [
Figure 5 Slightly]
Conclusion The large radiator assembly has good heat dissipation performance and can effectively heat dissipation.
They are great both in terms of design functionality and welding, but it\'s hard to rework.
They are assembled in a highly controlled process with unrestricted heating.
However, when rework is required, there are serious thermal limitations due to the fragile and subtle nature of the barrel, liner and mask.
The new rework method provides a controlled process using low operator requirements.
This method can also be used to repair the ball dirt, chip
Scalable package and flip chip options
Weld and remove holes.
While investment in equipment is required, other methods may not be able to perform safe and reliable rework of these expensive components.
Richard Garnick is the chief process engineer at AL Huntsville Benchmark Electronics; e-mail: richard. garnick@bench. com.
Under the management of Ronald ismarketing, air
Project of CT Seymour Vac; e-mail:ron. wachter@air-vac-eng. com.
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