The BGA repair steps are basically the same as the traditional SMD repair steps,

and the specific steps are as follows: 1. Disassemble the BGA

(1) Place the surface assembly board that needs to be disassembled on the workbench of the repair system.

(2) Select the square hot air nozzle that matches the size of the device,

and install the hot air nozzle on the connecting rod of the upper heater. Pay attention to the smooth installation.

(3) Fasten the hot air nozzle on the device, paying attention to the surrounding area of ​​the device. The distance is uniform.

If there are components around the device that affect the operation of the hot air nozzle,

these components should be disassembled first, and then re-soldered after the repair is completed.

(4) Select the suction cup (suction nozzle) suitable for sucking the device to be disassembled,

adjust the height of the vacuum suction pipe device for the suction device,

lower the suction cup to contact the top surface of the device, and turn on the vacuum pump switch.

(5) Set the disassembly temperature curve.

It should be noted that the disassembly temperature curve must be set according to the size of the device,

the thickness of the PCB, etc., and the disassembly temperature of the BGA.

(6) Turn on the heating power and adjust the amount of hot air.

(7) When the solder is completely melted, the device is sucked by the vacuum pipette.

(8) Lift the hot air nozzle upward, turn off the vacuum pump switch, and catch the disassembled device.

2. Remove the residual solder on the PCB pad and clean this area;

(1) Use a soldering iron to clean and level the residual solder on the PCB pad, and use a desoldering braid and a flat spade-shaped soldering iron to clean up.

Be careful not to damage the pads and solder mask.

(2) Use a cleaning agent such as isopropyl alcohol or ethanol to clean the flux residue.

3. Dehumidification treatment: Since PBGA is sensitive to moisture,

it is necessary to check whether the device is damp before assembly, and dehumidify the damped device.

(1) Dehumidification treatment, the device needs to be dehumidified before mounting.

The method of dehumidification can use electric heating blast drying oven and bake at 125±℃ for 12-20h.

(2) Precautions for dehumidification treatment:

(a) The device code should be placed in a high temperature (greater than 150℃) antistatic plastic tray for baking.

(b) The oven should be well grounded, and the operator should wear a well-grounded anti-static bracelet on the wrist.

4. Ball planting

1): Remove the residual solder on the bottom pad of the BGA and clean it. Use a soldering iron to clean and level the residual solder on the PCB pad.

Desoldering braided tape and flat spade-shaped soldering iron tip can be used for cleaning.

Be careful not to damage the pad during operation. and solder mask.

Use special cleaning agent to clean the flux residue.

2): Generally, high-viscosity flux is used for printing flux on the bottom pad of BGA, which plays the role of bonding and soldering.

It should be ensured that the flux pattern is clear and does not flow after printing.

Sometimes solder paste can be used instead.

When using solder paste, the metal composition of the solder paste should match the metal composition of the solder ball.

When printing, use a special small template for BGA.

The thickness of the template and the size of the opening should be determined according to the ball diameter and ball distance.

After printing, the printing quality must be checked.

If it is not qualified, it must be cleaned and reprinted. 3): select solder balls

When selecting solder balls, consider the material of the solder ball and the size of the ball diameter.

At present, the solder paste material of PBGA solder balls is generally 63Sn/37Pb,

which is consistent with the materials currently used for reflow soldering.

Therefore, solder balls that are consistent with the BGA device solder ball materials must be selected.

The selection of solder ball size is also important.

If high viscosity flux is used, solder balls with the same diameter as BGA device solder balls should be selected; if solder paste is used,

solder balls should be selected with a smaller diameter than BGA device solder balls. 4): Ball planting..

A) If there is a bead planting table, choose a template that matches the BGA pad.

The size of the opening of the template should be 0.05–0.1mm larger than the diameter of the solder balls, and the solder balls should be evenly distributed.

Sprinkle the ground on the stencil, shake the beading table, and roll the excess solder balls from the stencil to the solder ball collecting groove of the beading table,

so that there is exactly one solder ball in each leak hole on the surface of the stencil.

Place the bead planting table on the workbench, suck the BGA device printed with flux or solder paste on the suction nozzle,

align it according to the method of mounting BGA, move the suction nozzle down, and mount the BGA device on the nozzle.

On the solder balls on the surface of the beading table template, then suck up the BGA device, and stick the solder balls on the corresponding pads of the BGA device with the help of the viscosity of the flux or solder paste.

Hold the outer frame of the BGA device with tweezers, turn off the vacuum pump, and place the solder balls of the BGA device on the workbench to check for missing solder balls.

If there are any, use tweezers to fill them up. ..

B) Using the stencil method, place the BGA device with the flux or paste printed on the workbench with the flux or paste face up. Prepare a stencil that matches the BGA pad.

The opening size of the stencil should be 0.05-0.1 mm larger than the diameter of the solder ball.

Use pads around the stencil to raise it, and place it on the top of the BGA device printed with flux or solder paste,

so that the stencil and the solder paste are printed.

The distance between the BGAs is equal to or slightly smaller than the diameter of the solder balls, aligned under a microscope.

Spread the solder balls evenly on the stencil, and remove the excess solder balls with tweezers,

so that there is exactly one solder ball in each leak hole on the surface of the stencil. Remove the template, check and fill in. ..

C) Manual Mounting Place the BGA device with the flux or paste printed on the workbench with the flux or paste face up.

Use tweezers or a suction pen to place the solder balls one by one like a patch. ..

D) When the stencil is processed by brushing an appropriate amount of solder paste, the thickness of the stencil is thickened, the size of the opening of the stencil is slightly enlarged,

and the solder paste is directly printed on the pad of the BGA. Solder balls are formed after reflow due to surface tension. ..

5: Reflow soldering After reflow soldering, the solder balls are fixed on the BGA device. ..

6: After the ball mounting process is completed after soldering,

the BGA device should be cleaned and mounted and soldered as soon as possible to prevent solder ball oxidation and device moisture.

. 5. BGA mounting BGA devices can generally be reused, but they must be placed after ball placement (see 13.3BGA placement process introduction). The steps of BGA mounting devices are as follows:

(1) Place the surface assembly board with the solder paste printed on the workbench of the BGA rework system.

(2) Select the appropriate nozzle and turn on the vacuum pump.

Pick up the BGA device, use the light source on the top of the camera to illuminate the BGA pads with solder paste printed on the PCB,

adjust the focus to make the image displayed on the monitor the clearest, and then pull out the BGA-specific reflective light source to illuminate the bottom of the BGA device to make the image the clearest.

Clear, and then adjust the X, Y, 9 (angle) knobs of the workbench to make the bottom image of the BGA device completely coincide with the PCB pad image, and the split image function can be used for large-sized BGA devices.

(3) After the bottom image of the BGA device and the PCB pad image are completely overlapped, move the suction nozzle down, mount the BGA device on the PCB, and then turn off the vacuum pump. 6. Reflow soldering

(1) Set the soldering temperature curve. Set the soldering temperature curve according to the specific conditions such as the size of the device and the thickness of the PCB.

In order to avoid damage to the BGA device, the preheating temperature is controlled at 100-125 °C.

The heating rate and temperature holding time are both critical, and the heating rate is controlled at 2-5 °C /s, the soldering temperature of BGA is about 15℃ higher than that of traditional SMD,

and the preheating temperature at the bottom of PCB is controlled at about 165℃.

(2) Select the square hot air nozzle that matches the size of the device, and install the hot air nozzle on the connecting rod of the upper heater, paying attention to the smooth installation.

(3) Fasten the hot air nozzle on the BGA device, and pay attention to the uniform distance around the device;

(4) Turn on the heating power and start welding.

(5) After welding, lift up the hot air nozzle and remove the PCB board. 7. Inspection of BGA welding quality inspection requires X-ray or ultrasonic inspection equipment.

In the case of no inspection equipment, the welding quality can be judged through functional testing, and the surface assembly board with the BGA welded can also be lifted up and viewed around the BGA.

Observe whether the solder paste is completely melted,

whether the solder balls are collapsed, and whether the distance between the periphery of the BGA and the PCB is consistent, and judge the welding effect by experience.