Important considerations when mounting the DMD include optical alignment, ensuring a good electrical connection, and control of the mounting loads (forces) applied to the DMD electrical and thermal areas. The DMD data sheet specifies the maximum loads for each of these areas. DMDs with pins do not require a continuous load on the DMD for a good electrical connection (as DMDs with pads do). The only load that needs to be applied to the DMD (electrical area) is that which is needed to keep the PCB from moving after it is installed.
- Good mounting practices include:
- Use of the DMD defined Datums ‘A’, ‘B’, and ‘C’ for optical alignment
- Control of part tolerances which contribute to changes in the loads applied to the DMD (gaps for springs, gaps between PCB and boss, etc…)
- A design that prevents interactions between loads applied to the thermal and electrical areas
- Preventing PCB from bending
- Fixing PCB in place without applying additional loads to the DMD
- Control mechanical forces on the DMD thermal and electrical interface areas to prevent them from exceeding those specified in the DMD data sheet (System Mounting Interface Loads section).
- Mechanical forces should be uniformly applied (even clamping pressure)
- Partial tightening of fasteners, order of tightening fasteners, possible use of a fixture
- Design Method to control of forces (Best method)
- Forces controlled by design details rather than use of fastener torques or special procedures
- Minimize force variations from part tolerances by use of coil springs, flat springs, shoulder screws
- Minimum and maximum force range easily determined and controlled
- Assembly Process Method to control of forces
- Forces controlled by use of fastener torque and special procedures
- Greater variation and uncertainty of force applied than Design Method of control
- Applied forces highly dependent on assembly person and process
- Torque value determined for a specific design (set of materials and fasteners used)
- Difficult to determine clamping forces from fasteners
These concepts can be modified to meet the specific requirements of the application and its environment. In so doing ensure the modifications allow the DMD specifications to still be met. The heat sinks included in the concepts are representative of the mechanical mounting features but not the thermal performance characteristics. The thermal characteristics of a heat sink or heat exchanger should be designed to ensure all the DMDs thermal specifications are met under all conditions.