|
Important considerations for mounting the DMD |
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 pads require a continuous load on the DMD for a good electrical connection. The load applied to the DMD electrical area is that which is needed to maintain a good electrical connection and general clamping to secure the DMD in place.
- 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…)
- Control part tolerances for features used to align the DMD, electrical interposer, and PCB
- A design that prevents interactions between loads applied to the thermal and electrical areas
- Preventing PCB from bending (clamp material and thickness)
- If additional loads are needed to secure the DMD they should be applied in a lateral direction to not apply 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, compressive washers, 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 (based on 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.
|
| .7 Size Ceramic Type-A DMD Mounting Concepts |
|
(Select Figures below or Mounting Concept Title for detailed information) |
 |
Dual Coil Springs Mounting Concept 9084
- TI Drawing 2519084
- Mechanical load on DMD thermal area is controlled by design (gap size and coil springs)
- Mechanical load on DMD electrical area is controlled by design (gap size and coil springs)
- Mechanical loads on the thermal and electrical areas are controlled independent of each other
- The DMD and PCB are attached first to establish an electrical connection. Heat sink is attached with seperate screws
- Important: Selection of coil springs and gap it fits are critical for control of mounting loads
- Best Method
|
 |
Coil & Flat Spring Mounting Concept 3566
- TI Drawing 2503566
- Mechanical load on DMD thermal area is controlled by design (gap size and coil springs)
- Mechanical load on DMD electrical area is controlled by design (gap size and coil springs)
- Mechanical loads on the thermal and electrical areas are controlled independent of each other
- The DMD and PCB are attached first to establish an electrical connection. Heat sink is attached with seperate screws
- Important: Selection of coil springs and gap it fits are critical for control of mounting loads
- Best Method
|
 |
Flat Spring Mounting Concept 3737
- TI Drawing 2503737
- Mechanical load on DMD thermal area is controlled by design (gap size and flat springs)
- Mechanical loads on DMD electrical area is NOT controlled by design but rather by assembly process (torque on screws)
- Mechanical loads on the thermal and electrical areas are NOT controlled independent of each other
- The DMD and PCB are attached to establish an electrical connection. Heat sink is attached with seperate screws
- Caution: Loads are harder to control and have greater variation. Great care is needed during assembly to prevent damage to the DMD. Torque amount and tightening of screws are critical to prevent damage to the DMD.
|