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Bad BGA welding in SMT chip processing and Solutions

Source: Lin Chuan precision article author: Lin Chuan precision time: March 2, 2020 18:31 reading: 1862

BGA: ball grid , BGA has smaller volume, better heat dissipation performance and electrical performance compared with TSOP; the storage capacity per square inch has been greatly improved, and the volume is only one third of that of TSOP package under the same capacity. In order to improve the efficiency of GBA placement, we summarize some BGA welding defects and solutions in SMT surface mounting process, and share them with you.

 Commonly used BGA in SMT processing

Commonly used BGA in SMT processing

The following figure shows the normal BGA welding process and effect, which can be compared with the defects described below.

 Process and effect of BGA welding in SMT
Process and effect of BGA welding in SMT

Bad BGA welding in SMT SMT process and Solutions

   1. Bubble

Bubbles (or blowholes) are not absolute bad phenomena, but if the bubbles are too large, they are easy to cause quality problems. The acceptance of bubbles has IPC standard. The bubble is mainly caused by the air in the blind hole not discharged in time during welding.

Ray: check the internal temperature of raw materials with ray

BGA Bubble Diagram

 BGA Bubble Diagram


Generally speaking, the bubble size should not exceed 20% of the sphere

 BGA bubble in SMT processing


   2. Lianxi

Even tin is also known as short circuit, that is, tin ball and tin ball in the welding process of short circuit, resulting in two pads connected, resulting in short circuit.

Solution: the factory adjusts the temperature curve, reduces the reflux pressure, and improves the printing quality

 In SMT processing, the red circle is the tin position
The red circle is connected with tin


  3. False welding

False soldering is also known as "head in pillow (hip)", which is caused by many reasons (solder ball or pad oxidation, insufficient temperature in the furnace, PCB deformation, poor solder paste activity, etc.). The characteristics of BGA false welding are "difficult to find" and "difficult to identify".

 Fabrication of bgsma in false welding
BGA false welding in SMT processing


 Side view of BGA false welding during SMT
Side view of BGA false welding during SMT

Solution: change solder paste with better active ingredients; adjust temperature curve to improve printing quality

   4. Dirty

In the process of welding, there may be foreign matters on the pad, which may lead to bad welding environment.

 Schematic diagram of BGA dirt acceptance in SMT processing

Schematic diagram of BGA dirt acceptance in SMT processing

Solution: before unpacking, check whether the package is broken, confirm whether the PCB pad is discolored, and return it to the supplier for treatment.

   5. Cold welding

Cold welding is not completely equivalent to false soldering. Cold welding is due to abnormal reflow temperature, which leads to incomplete melting of solder paste, which may be caused by temperature not reaching the melting point of solder paste or insufficient reflow time in reflow zone.

 SMT processing GBA cold welding

SMT processing GBA cold welding

Solution: the factory adjusts the temperature curve to reduce vibration during cooling


   6. Tin ball cracking

This is a defect in BGA production process. Passing through the furnace after SMT placement will cause false soldering between solder ball and GBA PCB. The defects caused by this problem are often ignored.

 BGA Solder Ball cracking in enlarged tin

BGA Solder Ball cracking in enlarged tin

Solution: the incoming inspection department shall sample the incoming materials and inspect them under the microscope.

  
The above is all the contents of "BGA bad welding and solutions in SMT SMT chip processing". I hope it can help your SMT processing and production. If you need more help, you can call 18928403435, or email: Luohua @ lcjmi.com, and we will provide you with the most professional service.

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