Micro Soldering Techniques SS3 Computer Hardware & GSM Repair Lesson Note

Subject: Computer Hardware and GSM Repair 

Class: SS3

Topic: Precision Soldering (IC Replacement and Jumpering)

The Art of Small Things

As mobile phones get thinner and more powerful, the parts inside get smaller. We have moved past basic soldering to Micro Soldering. This isn’t just about melting lead; it is about steady hands, the right temperature, and understanding how microscopic “legs” (pins) connect to the motherboard.

In this lesson, we will focus on the two most important skills for a professional technician: Replacing Integrated Circuits (ICs) and Jumpering broken connections.

Essential Tools for Micro Soldering

You cannot do this work with a regular “big” soldering iron. You need precision:

• Hot Air Rework Station: Uses controlled hot air to melt the solder under a chip without touching it.
• Micro Soldering Iron (T12 or JBC type): Has a very fine, needle-like tip for tiny spots.
• Microscope: Your eyes cannot see the gaps between IC pins. A 7x to 45x magnification is standard.
• Flux: This is the “magic liquid.” It cleans the metal, prevents oxidation, and helps the solder flow exactly where it should go.
  
• Solder Wick (Desoldering Braid): A copper braid used to “soak up” old solder from the board.

Integrated Circuit (IC) Replacement

An IC is a “chip” with many tiny balls of solder underneath it. This is called a BGA (Ball Grid Array).

Step-by-Step: Removing an IC

1. Protection: Cover nearby plastic parts (like connectors) with Kapton tape or heat shields so they don’t melt.
2. Apply Flux: Put a little flux around the edges of the chip.
3. Heating: Use the hot air gun (usually set between 330°C and 380°C) in a circular motion.
4. The “Nudge” Test: Once the solder melts, gently touch the side of the chip with tweezers. If it “wiggles” and returns to its spot, the solder is molten.
5. Lifting: Lift the chip vertically with tweezers. Do not drag it, or you will tear the copper pads off the board!

Step-by-Step: Reballing and Installing

• Cleaning: Use the soldering iron and wick to make the pads on the motherboard perfectly flat.
• Reballing: Use a Stencil and Solder Paste to create new, uniform balls on the bottom of the new IC.
• Alignment: Look for the Directional Dot (a tiny mark on one corner of the IC). It must match the mark on the motherboard.
• Soldering: Apply heat until the chip “settles” into place. Surface tension will actually pull it into the perfect center.

Jumper Techniques (The “Bypass” Surgery)

Sometimes, a track (the copper wire inside the board) breaks because of water damage or a heavy fall. Since we cannot replace the track inside the board, we run a “Jumper Wire” outside.

The Process:

1. Identify the Break: Use your schematic to find where the signal starts and where it ends.
2. Scratch the Surface: If the pad is gone, use a surgical blade to gently scratch the green mask until you see the shiny copper “path.”
3. Tinning the Wire: Use 0.02mm Enamelled Copper Wire. This wire has a thin plastic coating so it doesn’t cause a short circuit if it touches other parts. You must “tin” the ends with solder first.
4. The Connection: Solder one end to the source and the other to the destination.
5. UV Green Oil: Once the wire is in place, cover it with UV Mask (Green Oil) and shine a UV light on it. This hardens the oil and “glues” the wire down so it never moves.

Common Mistakes to Avoid

• Too Much Heat: If you heat the board for too long, the layers will separate (Popcorning), and the board is ruined forever.
• Static Electricity: Always wear an ESD (Anti-static) wrist strap. A tiny spark from your finger can kill a CPU before you even start.
• Using Too Much Solder: In micro soldering, “less is more.” Too much solder causes “bridges” (where two pins touch and cause a short).

Summary

Micro soldering is a skill of patience. It turns a “dead” phone into a working one and is one of the highest-paid skills in the repair industry. Practice on “scrap” boards before attempting a repair on a customer’s device!

Practical Review

1. What is the purpose of Flux in micro soldering?
2. Why must we pay attention to the Dot on the corner of an IC?
3. Describe what UV Green Oil is used for during a jumper repair.
4. If a phone nearby has a plastic battery connector, what should you do before using the hot air gun?