The repair method of power device
Technical field
The present invention relates to the repair method of the repair method of device, particularly a kind of power device.
Background technology
Along with the microminiaturization of device, the development of miniaturization, its integrated level is more and more higher, the heat dissipation problem of device becomes the focus that industry is paid close attention to, encapsulation for the ease of heat radiation, it is more and more that chip directly is attached to the heat radiation form of large bonding pad by PCB (printed circuit board), as shown in Figure 1, comprising lead frame 1, silicon chip 2, silicon chip adhesion layer 3, central heat sink pad 4 and embedding 5.Its PCB pad design as shown in Figure 2, the bonding area of the bottom center of this encapsulation heat radiation pad will directly determine the radiating efficiency of device and function to realize.
Reprocess at the device of device bottom for solder joint, usual way () is: reprocess platform fusing solder joint and remove device-cleaning PCB pad-on PCB or device with hot blast and put by steel mesh seal tin cream or some tin cream-subsides that new unit-reprocessing platform with hot blast heats and weld device.
Reprocess for the visible wing four limits lead-in wire flat packaging of all solder joints of device (QFP), usual way (two) is: with flatiron or heat gun with the fusing of device solder joint and remove device-cleaning PCB pad-subsides and put new unit-add solder stick with flatiron also to weld device pin one by one.
In the QFP device rework process of this band central authorities big heat radiation pad, as having the following disadvantages with the seal tin method in the method one:
1,, needs to make the little steel mesh of seal tin as printing tin cream with steel mesh;
2, seal tin is difficult to guarantee to print tin coplanarity and good stripping result on PCB or device;
3, seal tin operation is had relatively high expectations to the operative employee;
4, because the Coplanarity Problems of peripheral pin may cause the peripheral pin rosin joint of QFP.
If will have the following disadvantages with the some process of tin in the method one:
1, needs special-purpose some tin equipment;
2, complex procedures increases and reprocesses cost;
3, the point tin cream used of tin is because its scaling powder scolder is higher, and layering is serious, can cause a tin quality not controlled.
4, the improper bonding area that will cause of some process of tin control does not satisfy the designs requirement less than 50% of pad, influence the radiating effect of device, shown in Fig. 3 X ray (X-Ray) effect as can be seen bottom the bonding area deficiency of solder joint.
As can reprocessing the device periphery solder joint, but can not finish welding process to the big heat radiation pad of bottom center with method two.
Summary of the invention
The invention provides a kind of repair method of power device, can not simultaneously make in the prior art to solve that to reprocess technology simple and direct and guarantee that fully the big heat radiation pad of bottom center welds sufficient shortcoming.
For this reason, the repair method of a kind of power device of the present invention comprises the steps:
A, remove power device from the heat radiation pad of printed panel;
The heat radiation pad of B, the above-mentioned printed panel of cleaning, and on this heat radiation pad, be coated with weld-aiding cream;
C, on the heat radiation pad of printed panel, place the scolder prefabricated film, and on this prefabricated film, be coated with weld-aiding cream;
D, on the scolder prefabricated film, paste and put new unit, this new unit is welded on the heat radiation pad of printed panel;
The peripheral pin of E, welding new unit.
Because adopt above-mentioned scheme, the present invention has following advantage:
1, can guarantee the bonding area requirement of center bottom solder joint well, and guarantee the welding quality of peripheral solder joint, thereby the assurance device function is normally realized;
2, need not make the little steel mesh of seal tin, tin printing clamp etc., reduce operational sequence, reduce cost, easy to operate.
Description of drawings
Fig. 1 is the power device schematic diagram that dispels the heat by pad in the prior art;
Printed panel pad schematic diagram in Fig. 2 prior art;
The effect schematic diagram of Fig. 3 prior art mid point process of tin welding;
Fig. 4 method flow diagram of the present invention;
Fig. 5 adopts the effect schematic diagram of the inventive method.
Embodiment
The present invention is in conjunction with the strong point of art methods one and method two, and the central heat sink pad and the peripheral pin of device welded in two steps.In the welding sequence of central heat sink pad, adopt prefabricated film can guarantee the requirement of central heat sink pad bonding area, satisfy device heat radiation requirement, by hand weldering, can eliminate the Welding Problems that peripheral lead coplanarity causes to peripheral pin.
Consult flow chart shown in Figure 4:
(1) at first reprocesses solder joint on the platform fusing printed panel central heat sink pad, former welding power device is removed with hot blast;
(2) will dispel the heat removings such as foreign material on the pad, and manual brushing one deck weld-aiding cream thereon.Carrying out the manual brushing of weld-aiding cream on the central heat sink pad can finish with a cotton balls, and weld-aiding cream should approach and uniformly;
(3) place the scolder prefabricated film at the central heat sink pad.The prefabricated film material is selected for use and the normal identical Sn63Pb37 of welding tin paste composition, and it is consistent with device central heat sink pad size to utilize blade or other shaping jig that it is treated to, and the prefabricated film of forming is attached on the weld-aiding cream of central heat sink pad.
(4) manual brushing one deck weld-aiding cream on prefabricated film.This layer weld-aiding cream should approach and evenly.
(5) new power device subsides are placed on the prefabricated film.
(6) reprocess platform with hot blast and add the new power device of thermal weld.
(7) the peripheral pin of the new power device of usefulness flatiron manual welding.
The new power device that adopts the welding of above-mentioned flow process as shown in Figure 5, X ray (X-Ray) design sketch after reprocessing from device as can be seen, it is better than prior art to reprocess effect.
Adopt the present invention, can guarantee the bonding area requirement of center bottom solder joint well, and guarantee the welding quality of peripheral solder joint, simultaneously easy to operate, reduce cost.