Jul22
What purpose of alloy metal of Cu, Ag, Zn, Sb, Bi added to solder paste?

post on July 22, 2021

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.

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Process, Quality, SMT, Soldering     WorkingBear    Views (7,078)     comments (1)
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Nov13
Why BGA soldering ball always crack(3)? IMC layer growth is a certain result to form the soldering joints

post on November 13, 2019

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.

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Design, EDX/EDS/SEM/IMC/FTIR,, SMT, Soldering     WorkingBear    Views (15,624)     comment (0)
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Oct30
Why BGA soldering ball always crack(2)? The composition of PCBA bonding-force

post on October 30, 2019

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.

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Design, SMT, Soldering     WorkingBear    Views (11,759)     comments (2)
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Sep25
Why BGA soldering ball always crack(1)? Stress > bonding-force

post on September 25, 2019

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!

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Design, SMT, Soldering     WorkingBear    Views (11,171)     comment (0)
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Dec19
What is IMC (Intermetallic Compound) in the electronic manufacturing industry？

post on December 19, 2018

What is IMC (Intermetallic Compound) in the electronic manufacturing industry？

What is the IMC, the Intermetallic Compound? We always heard the manufacturing engineer or some of Mechanical Engineer talking about this keyword when discussing  soldering quality or electronic component drop issue. So, what is the role of IMC layer in soldering? Does the IMC layer affect soldering strength and solderability? What is the ideal IMC layer thickness?

The IMC is the abbreviation of Inter-Metallic Compound in the electronic manufacturing industry.  The IMC usually grows between the solder alloy and Cu or Ni substrate for the Printed Circuit Board Assembly (PCBA). The IMC is neither a pure metal element nor alloy (Some expert think IMC is a kind of alloy). The IMC is a chemical compound that chemically combined by two or more elements. So, you may see the chemical formula of IMC like Cu6Sn5、Ni3Sn4、AuSn4 ,and so on.

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Process, Soldering     WorkingBear    Views (38,947)     comments (3)