The Assembly Process
How poor assembly procedures affect you.
Module assembly can have a considerable effect on how the end product works. Is it automated? Or are people soldering on parts by hand in a warehouse? You probably won't be able to tell if the parts went through proper material storage, screen print, and reflow processes during assembly just by looking at them. However, these are some of the practices that play key roles in the short and long term reliability of your memory module.
During the reflow process, (where the DRAM components are permanently attached to the PCBs) the boards go through a heat cycle of a few hundred degrees. If they are heated too quickly or remain at an elevated temperature too long, they can be significantly damaged. However, this damage may not be visible. If the parts weren't properly stored, any large amount of moisture that was trapped inside tends to expand and cause a failure almost immediately. Additionally, the reflow process can sometimes affect the module just enough so that it performs properly initially but degrades over time. This can result in memory that doesn't work by the time the end user gets it, or memory that fails intermittently.
Another item that drives process improvements and widens the gap between upper and lower echelon assemblers is component packaging. More and more DRAM components are being packaged in ball grid arrays (BGAs). Instead of having leads that come out from the side of the chip, the chip attaches to the PCB through solder spheres, or balls, that are on the bottom of the component. BGAs can be placed using the same equipment that is used to place leaded components. However, the tricky part is verifying that the solder joints are good.
Since the solder joint is under the body of the device, you cannot visually look at it and determine if it is acceptable. The only way to inspect these packages is with an x-ray machine. And the only way to replace or repair the part is with specialized equipment.
Even the best memory chips in the world can be damaged by poor assembly techniques.
Testing the final product »