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! read more…》
What is the IMC? We always heard the manufacturing engineer talking about this keyword when discussing to the soldering quality. 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 IMCt usualy 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.
Is that possible both solder joint bridging and open solder joint defect happen at same BGA (Ball Grid Array) or CSP (Chip Scale Package) device?
It is hard to see both solder joint bridging and open solder joint defect happen at same BGA device in the general situation, but it is still possible. There is a case that BGA substrate and PCB has a big deviation of CTE (Coefficient of Thermal Expansion) then make the BGA substrate with smile-up curve (concave) deformation and PCB with cry-down curve (convex) due to longer TAL (Time Above Liquidus) or big temperature deviation between above and below heater 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.
Recently WorkingBear got complaint from R&D and ask increase the solder paste volume on the MLCC (Multi-Layer Ceramic Capacitor) component pads to improve the capacitor broken issue. R&D said he had verified that the capacitor’s footprint in the board design is correct and followed manufacturer’s design guidelines. However, looks like there is not enough solder paste to form proper heel fillet on the terminal of capacitor. This insufficient solder paste volume make the solder cracking?