BGA and SMD Rework Guide: Steps, Tips & Ball Planting

Table of Contents

Ordinary Rework

Principle of Ordinary SMD Rework System: Heat airflow is concentrated on the pins and pads of surface mount devices (SMDs) to melt solder joints or reflow solder paste, enabling disassembly and welding functions.
The main differences between rework systems from different manufacturers lie in the heating source or the mode of heat airflow. Some nozzles direct hot air above the SMD. From the perspective of component protection, it is preferable to choose a rework system with airflow circulating around the PCB. To prevent PCB warping, a rework system with preheating function for the PCB should also be selected.

BGA Rework

Steps for BGA rework using HT996:

1. Disassemble BGA

• Clean the residual solder on the PCB pads with a soldering iron until smooth. Use desoldering braid and a flat-tipped soldering iron head for cleaning, and take care not to damage the pads or solder mask during operation.

• Clean the flux residue with a special cleaning agent.

2. Dampness Removal Treatment

• Since PBGA is sensitive to moisture, check whether the component is moisture-sensitive before assembly, and perform dampness removal treatment on moisture-affected components.

3. Print Solder Paste

• As other components are already mounted on the surface assembly board, a special small BGA stencil must be used. The stencil thickness and opening size should be determined according to the ball diameter and pitch. After printing, the printing quality must be inspected. If unqualified, the PCB must be cleaned and dried before reprinting. For CSP with a ball pitch below 0.4mm, solder paste printing can be omitted, so no rework stencil is needed—simply apply paste flux directly to the PCB pads. Place the PCB with components to be removed into a soldering furnace, press the reflow soldering button, wait for the machine to complete the set program, press the in/out button at the highest temperature, remove the component to be detached with a vacuum pickup pen, and cool the PCB.

4. Clean Pads

• Clean the residual solder on the PCB pads with a soldering iron until smooth (same method as step 1).

5. Dampness Removal Treatment

• Repeat the same process as step 2.

6. Print Solder Paste

• Repeat the same process as step 3.

7. Mount BGA

• For new BGAs, check for moisture sensitivity. If moisture-affected, perform dampness removal treatment before mounting.

• Removed BGA components can generally be reused but must undergo ball planting treatment first. The BGA mounting steps are as follows:
  A. Place the surface assembly board with printed solder paste on the workbench.
  B. Select an appropriate suction nozzle, turn on the vacuum pump, pick up the BGA component, align the bottom of the BGA with the PCB pads completely, lower the nozzle to mount the BGA on the PCB, and then turn off the vacuum pump.

8. Reflow Soldering

• Set the soldering temperature according to specific conditions such as component size and PCB thickness. The soldering temperature for BGA is approximately 15°C higher than that for traditional SMD.

9. Inspection

• If no light passes through, it indicates bridging or solder balls between solder joints.

• Irregular or skewed solder ball shapes indicate insufficient temperature or incomplete soldering, where the self-alignment effect did not fully occur during solder reflow.

• Solder ball collapse degree: Related to soldering temperature, solder paste volume, and pad size. With reasonable pad design, a collapse of 1/5 to 1/3 in the distance between the BGA bottom and the PCB after reflow soldering is normal. Excessive collapse indicates excessively high temperature, prone to bridging.

• Inconsistent distances between the BGA periphery and the PCB indicate uneven temperature distribution.

• BGA soldering quality inspection requires X-ray or ultrasonic inspection equipment. In the absence of such equipment, functional testing can be used to judge soldering quality, or experience-based inspection can be applied.

• Hold the surface assembly board with the soldered BGA up and visually inspect the periphery of the BGA against light. Check for light transmission, consistency of the distance between the BGA periphery and the PCB, complete melting of the solder paste, regularity of solder ball shape, and degree of solder ball collapse.

Ball Planting Process

1. Remove Residual Solder and Clean BGA Bottom Pads

• Clean the residual solder on the BGA bottom pads with a soldering iron until smooth (same method as step 1 of BGA disassembly).

• Clean the flux residue with a special cleaning agent.

2. Print Flux on BGA Bottom Pads

• High-viscosity flux is generally used to provide adhesion and soldering assistance, ensuring clear flux patterns without bleeding after printing. Solder paste can sometimes be used instead, with its metal composition matching that of the solder balls.

• Use a special small BGA stencil for printing, with thickness and opening size determined by ball diameter and pitch. Inspect printing quality after completion; reprint after cleaning if unqualified.

3. Select Solder Balls

• Consider both the material and diameter of the solder balls. Currently, PBGA solder balls typically use 63Sn/37Pb solder paste, consistent with reflow soldering materials, so solder balls must match the BGA component’s material.

• Solder ball size is also critical: use the same diameter as the BGA component’s balls with high-viscosity flux, and slightly smaller diameters with solder paste.

4. Ball Planting
   A) Using a Ball Planter

   B) Using a Stencil Method

   C) Manual Mounting

   D) Excessive Solder Paste Brushing Method

• Thicken the stencil and slightly enlarge the openings during fabrication, then print solder paste directly onto the BGA pads. Solder balls will form after reflow soldering due to surface tension.

• Place the BGA component with flux/solder paste printed on the workbench (flux/solder paste side up). Use tweezers or a suction pen to place solder balls individually, similar to component mounting.

• Place the BGA component with flux/solder paste printed on the workbench (flux/solder paste side up). Prepare a matching stencil with openings 0.05–0.1mm larger than the solder balls. Elevate the stencil with spacers above the BGA, ensuring the distance between the stencil and BGA is equal to or slightly smaller than the ball diameter, and align under a microscope. Scatter solder balls on the stencil, remove excess with tweezers, leaving one ball per aperture. Remove the stencil, inspect, and replenish missing balls.

• If a ball planter is available, select a stencil matching the BGA pads, with opening sizes 0.05–0.1mm larger than the solder ball diameter. Evenly scatter solder balls on the stencil, shake the planter to roll excess balls into the collection groove, leaving one ball per stencil aperture.

• Place the planter on the workbench, pick up the BGA component with flux/solder paste printed using a suction nozzle, align it as in BGA mounting, lower the nozzle to attach the BGA to the solder balls on the planter stencil, then lift the BGA—solder balls will adhere to the pads via flux/solder paste viscosity. Hold the BGA by its outer frame with tweezers, turn off the vacuum pump, place it on the workbench with the solder ball side up, and check for missing balls, replenish with tweezers if necessary.

5. Reflow Soldering

• Perform reflow soldering to fix the solder balls on the BGA component.

6. Post-Soldering

• After completing the ball planting process, clean the BGA component thoroughly and proceed with mounting and soldering as soon as possible to prevent solder ball oxidation and component moisture absorption.