In the reflow phase of module assembly, memory chips are permanently attached to PCB (printed circuit board). Once the chips have been attached, the new module undergoes temperature testing and is put through a heat cycle of several hundred degrees. If the new module is heated too quickly or remains at an elevated temperature for too long, it can be significantly damaged (and the damage will not be visible). Also, if the components weren't properly stored prior to reflow, large amounts of trapped moisture can expand and cause a module failure. Even worse, a poorly executed reflow process can provide a false sense of security to a low quality assembler. If the reflow isn't adequately prepared for (or if it's performed incorrectly), modules may perform well enough to pass initial testing, but degrade significantly over time, making them useless to the end consumer. The result? Memory that looks good in the packaging, but that doesn't work by the time you install it, or memory that fails intermittently.
Another assembly practice that separates high and low quality assemblers is component packaging. In our thirty-plus years of memory manufacturing, we've noticed that more and more DRAM components from other assemblers are being packaged in ball grid arrays (BGAs). This is problematic because instead of having leads that come out from the side of the chip, the chip attaches to the PCB through solder spheres (balls) that are on the bottom of the component. BGAs can be placed using the same equipment that is used to place leaded components, but this is a concern because some solder joints aren't acceptable for use. Since the solder joint is under the body of the device, it's unable to be examined for acceptability. 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 if a memory assembler uses the best components available to build modules, they can be damaged through poor assembly and you'd never know the difference.
Individual module testing
The third assembly practice that differentiates high and low quality assemblers is how the finished (assembled) modules are tested. Some assemblers test only a small sample of modules and call the entire batch good based upon an "acceptable defect level." These companies argue that it's cheaper to get a certain amount of returns than it is to detect and/or prevent them. While this may be true for their bottom line, if you're in the small percentage of users who ends up with a failed part, you probably don't think it's a good idea. We don't either. Every single Crucial memory module has been individually tested at the component, module, and functional levels. Your system's performance is important!
There are several other post-assembly tests that are important. You'll want your memory assembler to take finished modules through a series of tests, including checking for opens and shorts, leakage, verifying refresh rates, and running pattern tests. The equipment to run these tests, however, is extremely expensive and requires a great deal of engineering support and a high level of commitment from the assembler. Instead of purchasing this equipment, many low quality assemblers opt for cheaper handheld testing devices, which only check for opens and shorts, and perform no additional testing.
Reputable assemblers will also qualify modules on a variety of motherboards. As processors and memory speeds become faster and faster, it's increasingly critical for modules to do more than just meet a list of specs. They must be proven to work in specific systems. Unfortunately, many assemblers consider comprehensive testing an unwarranted expense, which can result in an unknown level of compatibility with your system. We believe differently. To us, quality and compatibility aren't costs to be counted; they're savings that we're proud to pass on to our customers.
The best way to ensure that your memory has been properly assembled
The best way to get premium-quality memory that you know has been properly assembled, tested, and approved is from Crucial. Since we're a brand of Micron, one of the largest memory manufacturers in the world, we're able to leverage three decades of manufacturing experience to ensure that the modules we sell are of the highest quality. Your system's performance is critical — don't leave it in the hands of a low quality assembler.