COB Description

Chip-On-Board (COB) technology involves mounting DRAM or Flash semiconductor die directly on a substrate without the need of a packaged component. Eliminating the FBGA or TSOP component package reduces the required substrate area and assembly weight. The saving in area can be as much as 20% in some cases. Using conventional printed circuit boards (PCBs) and standard wire bonding technology, COB technology can yield up to a factor of 5 in weight and volume reduction. COB technology also reduces the number of interconnects between an active die and the substrate (i.e., the package pins), which improves the overall circuit speed, leads to higher clock rates, better electrical performance and improved signal quality and increases the overall reliability of the module. A coating of an Epoxy encapsulent (or Glob Top) is applied that hermetically seals and protects the die and the wire bonded interconnections. The Glob Top also acts like a heat spreader between dies, improves heat emission, adds low coefficients of thermal expansion (CTEs), and provides a hermetically sealed module assembly. The die is glued directly to the PCB and provides for increased heat dissipation from the die through the PCB. Swissbit encapsulates the semiconductor die onto the PCB as a total module package, the complete assembly is extensively temperature tested as a unit, not separate components prior to SMT assembly. This also enables Swissbit to offer its line of COB modules in four temperature grade levels.

COB Features and Benefits

A COB memory module as offered by Swissbit provide customers with the following advantages:

• Typically Swissbit SODIMMS are 1.00” (25.4mm) high, low profile format. Typical SMT modules are 1.25” (31.75mm). This enables Swissbit’s modules to be used in more applications and allows better airflow.
• COB modules are 3.0mm thin; typical SMT modules are 3.8mm thick. A thinner design allows for better air flow around the installed module in most applications resulting in cooler operation.
• The thermal properties of Swissbit modules are superior to typical SMT modules. COB modules dissipate heat more efficiently and will run lower die junction temperatures in demanding convective cooling conditions. A cooler operating module runs faster and lasts longer.
• Our COB module has less lead frame connections then the typical SMT modules, which results in better signal integrity and higher reliability.
• Swissbit COB modules are available in commercial temperature grade (0°C to +70°C) and three extended temperature grades up to industrial grade (-40°C to +85°C).
• COB modules accept conformal coating better then the typical SMT modules do to their low profile and Glob Top encapsulation.
• Swissbit COB modules are inherently ruggedized for shock and vibration due to the COB technology and the Glob Top encapsulation process; typical SMT modules are not ruggedized.
• Swissbit COB modules are burned in and 100% tested at the module level as finished product, not at the IC level before assembly.
• All Swissbit COB modules are RoHS compliant.