Conventional SMT assembly is known as a two dimensional process. The reason for this is simple – most PCB designs are created with only two sides for component placement. Generally, SMT assembly consists of horizontal component placement. For many users and manufacturers, SMT may seem like a singular, sole method. However, this is not the case. Another option that PCB manufacturing organizations have is to utilize Package on Package assembly (PoP).
What Differentiates PoP from Traditional SMT Assembly
There are two basic differences between traditional SMT and PoP. In PoP, the components are placed in successively layers, i.e., on top of one another. Also, the SMT method involves applying solder paste for printing on a single horizontal plane. This method cannot be used in PoP since the components are stacked on top of each other.
For PoP, the components that are placed on top of existing parts need to have flux or special dipping solder paste applied at the time of assembly. The ability to assemble PoP devices requires two main changes from the standard SMT assembly process:
• Apply a layer of flux to a few or all components.
• The capability to stack components on top of one other.
These SMT assembly requirements are new compared to the technologies and hardware that are being used. PoP assembly is not an extremely difficult. A basic understanding of the assembly requirements, as well as the application requirements is required. Depending on the specific application, a variety of assembly processes can be used.
Assembly Method Types within PoP
The main methods of PoP assembly are “pre-joined”. These method apart is the assembly process.
Prejoined Assembly
The pre-joined method of assembly uses a two-part process. The first part involves stacking the devices, later to be sent for assembly. This step is the same as standard SMT. Components are placed on other devices in a carrier. The second part involves sending the carrier through a reflow process to join the devices. The pre-joined devices are then re-packaged for picking by the assembly system (normally a tray). These devices are then returned to the placement machine for stacking or placement on a device. In some cases, one layer is added at a single time, and the stack goes to reflow after each layer. In other cases, several pre-joined parts are stacked together after the initial process for creating the pre-joined devices.
PoP assembly service can be used as a solution driven alternative to traditional SMT assembly. It is requires little time and investment for addition and use. The methods within the assembly can be used after understanding the application requirement.