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!
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.
Is that possible for both solder joint bridging and open solder joint defect occur in the same BGA (Ball Grid Array) or CSP (Chip Scale Package) device?
It is rare to observe both solder joint bridging and open solder joint defects simultaneously in a BGA device under normal circumstances, but it is still possible. In cases where the BGA substrate and PCB exhibit a significant deviation in CTE (Coefficient of Thermal Expansion), the BGA substrate may deform with a concave smile-up curve, while the PCB may deform with a convex cry-down curve due to longer TAL (Time Above Liquidus) or significant temperature variation between the upper and lower heaters in the reflow oven.
Printing the solder paste on the PCB (Printed Circuit Board) and go through reflow oven to re-melt the solder paste and solder the electronic components on PCB is most common process in today’s electronics manufacturing industry. Printing the solder paste on the PCB just like painting on the wall. The only different is solder paste printing ask more accurately position and must control the solder paste volume on each pad. It requires a certain jig call “stencil” is a sheet-metal made and have designate aperture on the position that needs to print solder paste.
Almost of current PCB assembly manufacturer apply the “stencil” jig to enhance the solder paste printing process to get more accurately printing position of solder paste and control the solder volume. Once the solder paste print shift from its pad too much then the solder will not joint the electronic component and PCB pad together. The solder paste volume over or less quantity will make solder short or open defect.
