Following last discussion, we learned that solder cracking is caused when the stress placed upon it exceeds the strength of the bonding force. However, it’s possible to address this issue by increasing the bonding force of the printed circuit board assembly (PCBA). By doing so, we can effectively eliminate solder cracking, making it a more reliable and robust technology for a wide range of applications.
Tin (Sn) based solder is still the best material for PCB (Printed Circuit Board) assembly in the modern industry today. The only difference is the lead (Pb) free from the solder base due to environmental concerns.
The melting point of tin (Sn) as 231.9°C (equivalent to 505°K) is hardly accepted by PCB assembly since most electronic components may not sustain such high temperatures. Maybe it shall say there are still lots of electronic components that can’t reach so high-temperature levels today yet. As a result, the solder powder should contain the majority of tin and a few other alloy components, such as copper (Cu), silver (Ag), indium (In), zinc (Zn), antimony (Sb), bismuth (Bi), etc, to reduce the melting point of solder paste and mass-produce the PCB assembly under lower energy.
The Intermetallic Compound (IMC) layer grows in the interface between Cu-based, Ni-based and Sn-solder is the certain result of the chemical reaction that forming the soldering joint. But the IMC layer is also the weakest location of the solder bonding-force.
As mentioned last page, the bonding strength of PCBA shall include a minimum of 5 defect positions. Identifying the growth of IMC is crucial in determining the quality of soldering. If there is no IMC layer grows between the solder alloy and Cu or Ni substrate, the electronic component and PCB will not be joined. However, the IMC layers are also the weakest point in the whole soldering strength structure. Why?
The IMC is the abbreviation of Inter-Metallic Compounds in the electronics manufacturing industry. The IMC layer is the certain result of the chemical reaction to form the soldering joint. WorkingBear likens the IMC layer just like a child born from the marriage of a girl and a boy.
This article will talk about the composition of the PCBA bonding-force.
There are numerous factors and elements involved in PCBA bonding force. However, Workingbear believes that we can utilize the findings of the red dye test to examine this issue. The Red Dye Penetration test of BGA have categorized cracks into five types of defect locations. These positions can also be applied to all soldering problems in PCBA.
What is the actual root cause of BGA solder ball cracking? Stress is higher than its bonding-forces.
The root cause of BGA solder ball cracked is stress higher than bonding-forces.
Stress is higher than bonding-force is the certain result of BGA solder ball cracked.
BGA solder ball cracked is the certain result of stress higher than bonding-forces.
Working-Bear spent lots of time to prepare this serial article. Don’t just do copy and paste to steal my babies. There will be total 13+1 articles in this blog mentioned the BGA (Ball Grid Array) component drop and solder balls cracked issue. The most concepts that you may know already but here I summary them together systematically and let you read them easily.
“Stress > Bonding-force”
is the root cause of electronic components drop from the PCB and solder crack.
This is not the first time that Working-Bear be challenged the soldering problem from R&D once the NPI run found any components has solder crack. Our RD always came to me and challenged why EMS can’t make thing right to guarantee the solderability. Some RD even ask me need to increase the solder paste volume to improve the soldering strength. It is really enough!
