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

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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Why BGA soldering ball always crack(3)? IMC layer growth is a certain result to form the soldering joints

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 most weakness location of the solder bonding-force.

As we meniotned in previous page that PCBA bonding-force shall include 5 kinds of defect positions at least. The IMC layers usually is the most weakness locations show on the solder bonding-force base on forming good PCBA solder. Why?

The IMC is the abbreviation of InterMetallic Compound in the electronica manufacturing industry. The IMC layer is the certain result of the chemical reaction to form the soldering joint. Working-Bear describes the IMC layer just like the girl and boy marry then have a child.

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Why BGA soldering ball always crack(2)? The composition of PCBA bonding-force

This article will talk about the composition of the PCBA bonding-force.

The PCBA bonding-force actually contains many items and factors. But working-bear think we can refer to the conclusion of red-dye test to discuss it. The BGA red dye and pry test summary the crack as 5 kinds of defect positions. These locations also can be applied to the PCBA all soldering issues.

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Why BGA soldering ball always crack(1)? Stress > bonding-force

What is the actual root cause of  BGA ball cracked? Stress is greater than its bonding-forces.

The root cause of BGA solder ball cracked is stress greater than bonding-forces.

Stress is greater than bonding-force is the certain result of BGA solder ball cracked.

BGA solder ball cracked is the certain result of stress greater 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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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 discussed to the soldering quality or component drop issue. So, what is the role of IMC layer in the soldering? Does IMC layer will affect the soldering strength and solderability? What is the best IMC layer thickness?

The IMC is the abbreviation of InterMetallic 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…etc.

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