PCB Tech - PCB problem Why can't the problem of DDR virtual soldering be intercepted even when the product executes the burn-in (BI)?

PCB problem Why can't the problem of DDR virtual soldering be intercepted even when the product executes the burn-in (BI)?

Recently, a product of the company encountered the problem of virtual soldering of DDR memory chips (chips). When actually sending personnel to the customer’s site for maintenance, they found that the product could not be turned on. Just press and hold the DDR IC to turn it on, but release the pressure. The product cannot be turned on after the DDR is in use.

The products have been 100% tested in the factory, and there is a 12H burn-in (B/I) program. How can there still be defective products flowing into the hands of customers? What is going on?

From the description of this problem, this should be a typical HIP (Head-In-Pillow, pillow effect) double-ball virtual soldering problem. This type of problem is usually caused by the high temperature of the FR4 of the IC chip or PCB flowing through the Reflow (reflow). Bending deformation occurs during the zone, and the solder ball of the BGA (Ball) and the solder paste printed on the PCB cannot be contacted and melted together after melting.

According to experience, generally 99% of HIP occurs on the outermost row of solder balls around the BGA. The reason is almost all that the BGA carrier board or PCB circuit board deforms and warps when the Reflow temperature is high. After the board is warmed up The amount of deformation is reduced, but the molten tin has cooled and solidified, thus forming the appearance of double balls close together.

HIP is actually a serious BGA solder defect. Although this type of defect rate is not high, it is easy to pass the internal testing procedures of the factory and flow to the customer's hands. However, after the end customer uses it for a period of time, the product will be It was sent back for repair due to poor contact, which seriously affected the company’s reputation and user experience.

However, it is obvious that all products are burned/in, and the production line is 100% through electrical testing. Why can't the problem of DDR virtual soldering be intercepted?

This is actually a very interesting question. The following is just personal experience, and does not mean that this is necessarily the case.

Imagine first under what circumstances will HIP show an open circuit (open)? Most of the cases should happen when the board is heated and begins to deform, that is, if the product is just turned on and is still in the cooling stage, the HIP double ball may show a false contact state, so there is no problem when the product is turned on. After a period of time, the product began to heat up, and gradually the plate began to deform slightly due to the heat, so an open circuit phenomenon appeared.

Therefore, the possible reasons for the electronic assembly factory (EMS, Electronics Manufacturing Service) not detecting the DDR empty welding are as follows:

The product was not powered on for testing when it was burned in (B/I). It is possible to just leave the product at a certain temperature for a certain period of time, without turning on the power for B/I. Of course, no problem can be detected. This most often occurs in factories that only produce circuit board assembly (PCA) .

The product is plugged in and turned on for burn-in (B/I), but it has not designed a program to run the DDR memory test. Some DDR solder joints may not affect the product's booting action, and there will be problems only when the program runs to certain memory addresses.

Assuming that the product is plugged in and tested for DDR memory during burn-in, some errors will disappear as long as it is restarted. If you do not record at any time during the burn-in process, it is very likely that there is no way to catch this type of DDR problem. . Therefore, it is best to perform self-test when the product is burning and record whether you have made an error or have been in the machine, so that you can really know whether there is a real burning problem during the burning process.

Therefore, if the program cannot just run to the functional position of the virtual solder when the product burn-in temperature rises, it is really not possible to detect the DDR with the HIP virtual solder problem. ipcb is a high-precision, high-quality PCB manufacturer, such as: isola 370hr PCB, high-frequency PCB, high-speed PCB, ic substrate, ic test board, impedance PCB, HDI PCB, Rigid-Flex PCB, buried blind PCB, advanced PCB, microwave PCB, telfon PCB and other ipcb are good at PCB manufacturing.