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• SMT technology • Package sizes introduction • Reworking defective SMD compon • Assembly components techniques • SMT placement equipment


BGA Rework Process Introduction

Author:admin Date:7/23/2012 10:39:46 AM

BGA Rework Process Introduction

1 .Introduction

Defects are caused by many reasons during soldering SMD components as empty soldering, short circuit and others, so repair is necessary. The rework process is simple for common SMD, resistor, capacitor, SOIC, SOJ, PLCC and others. With small alignment are more and more in electronic products, lots of BGA, CSP, QFP and others are more and more, so rework stations become good helpers for operators.

2. How to Choose Rework Station

Main differences of rework stations are heat source and heat mode; Take example only upper heat or upper and lower both heating, some can set temperature curve. Considering protecting components, the upper and lower both heating system are better. To prevent PCB warping during repairing, preheat function in the rework system is better. PCB fix, BGA position and others are important consideration.

3 .Rework process

1) BGA disassemble

Remove BGA chip with rework system and clean solder residue on PCB with solder iron to make solder pad flat; clean and remove flux residue with special cleaner.

2) BGA dry

Please check all BGA chips dry or damp; put damp BGA components into dry box to dry.

3) Print solder paste

Print solder paste on disassemble location before soldering BGA; small and special BGA stencil is necessary because there are other components on the board; Thickness and size of stencils are decided by BGA ball diameter and distance.

For CSP whose ball diameter is <0.4mm, operators can cover flux on PCB solder pad directly.

4) Mount BGA chips

Set rework program and put dry BGA into preparation location; rework system will take it automatically and then place it into soldering location.

5) Solder

Set soldering temperature according BGA size, PCB thickness and others; then rework station will complete soldering process.  

4.BGA reball

BGA Reball is necessary if want to use BGA which has been disassemble again.  

1)Remove and clean PCB solder residue on BGA with solder iron; in the meantime clean flux residue with special clean liquid.

2) Print BGA flux at the bottom solder pad (the BGA flux should be high viscosity, solder paste can replace flux). Small and special BGA stencil is necessary because there are other components on the board; Thickness and size of stencils are decided by BGA ball diameter and distance.

3) Choose solder ball: Material and diameter of solder ball are very important. The material of solder ball has to be same with BGA pad; Size of solder ball is decided by flux or solder paste. If it is solder flux, ball size should be same with BGA new ball; if it is solder paste, ball size should be smaller.

4) Reball: choose suitable BGA stencil if operator use BGA reball kit. The opening size of stencil is larger 0.1mm than diameter of solder ball, then put solder ball even on BGA stencil and shake reball kit that can let surplus solder ball fall into collect box and ensure one solder ball is on one hole.

Take BGA printed flux or solder paste with BGA nozzle by vacuum pump, pick and place BGA onto the surface of solder balls which are on the reball kit; Take BGA and put it on relate solder pad; Close vacuum pump and check solder balls whether missing, if missing please fill them with tweezers.

With BGA stencil to reball is another way. Firstly put the side which has BGA solder ball is up on the table; The side has been printed solder paste or flux. Put stencil

5) Reflow solder: solder BGA in the reflow oven according to setting temperature curve to fix tin ball on BGA parts.

6) Use: Clean reball BGA and use it in short time; and prevent tin ball oxide and damp.