Mounting and Soldering of High Power Devices

As we achieve higher power levels of operation for passive terminations, attenuators, and resistors, it becomes increasingly important to find new effective methods of heat removal. Included in these methods must also be a thorough understanding of the customers’ requirements and his methods of heat mitigation.

Good soldering methods for all “tab” and SMD mounted devices are imperative in order to achieve the maximum performance from the component. RoHS solder compatibility per IPC-A-610 is important so that both compliance and good solder connections are achieved.

FOR SMD MOUNTING OF COMPONENTS

The following considerations are recommended:             SEE FIGURE 1

  1. Use thermal vias whenever possible around the chip.
  2. Install the maximum possible number of vias while still maintaining good soldering.
  3. The circuit board to which the component is to be mounted should have high density copper cladding in order to maximize heat transfer.
  4. Mounting footprints for SMD pads should be at least .010″ larger than the actual chip pads so as to aid in heat removal.

HEAT SINK MOUNTED COMPONENTS                              SEE FIGURE 2

All tab constructed components (chips and flanges) must have the proper stress relief between the customer’s circuit and the tab on the component. This stress relief is usually a “top hat” bend in the tab that modifies the elevation of the tab with respect to the PWB. Component General highly recommends that this stress relief be used in all applications as shown in Figure 2.

TAB MATERIAL

Both flanged  and flangeless components are supplied with tabs for connection to the customer’s circuit. The tab is made out of beryllium copper and gold plated. This tab material can be formed (via fixtures) to provide stress relief. It is also firm enough to retain its shape and position. This eliminates tab movement/damage during shipping.

SOLDER INFORMATION

Generally, most solder paste formulations including “no clean” and water soluble fluxes are compatible with Component General’s resistive product line. It is preferred to lay out a solder pattern such that minimum “voiding” will occur under the chip being soldered.

SOLDER REFLOW

Soldering can be accomplished by two (2) traditional methods-hot plate and convection reflow. For the hot plate method, the plate must be set to 20-50 degrees C above the reflow temperature of the chosen solder. However, the hot plate temperature should not exceed +320 degrees C. Beyond +320 degrees C, components may begin to suffer damage if exposed for any long period of time. Always consult the solder and flux data sheets for the chosen materials before attempting component soldering. For standard Component General components, use the following chart as a reference.

COMPONENT: SMD
SOLDER: PASTE
SUGGESTED SOLDER: INDIUM 8.9
SUGGESTED FLUX: NON NEEDED

COMPONENT: CHIP
SOLDER: PASTE/PREFORM
SUGGESTED SOLDER: INDIUM 8.9 OR SAC 305
SUGGESTED FLUX: 2% NC-9 FLUX COAT

COMPONENT: FLANGED PART
SOLDER: WIRE
SUGGESTED SOLDER: .020″ CORE 230
SUGGESTED FLUX: TACFLUX 18

COMPONENT: NO FLANGE
SOLDER: PASTE/PREFORM
SUGGESTED SOLDER: INDIUM 8.9 OR SAC 305
SUGGESTED FLUX: 2% NC-9 FLUX COAT

SCREW TORQUES FOR MOUNTED FLANGED COMPONENTS

Chart assumes the use of type 316 stainless steel hardware

SIZE                     TORQUE IN INCH-POUNDS

2-56                       2.6

4-40                      5.5

6-32                      10.1

8-32                      20.7

FLANGE BASE MATERIALS

Generally, OFHC type 110 copper is used for base mounted products. However, when the component is subjected to either high power or pulsed temperature cycled applications, the use of a copper tungsten base should be considered. The copper tungsten material is able to more adequately match the temperature coefficient of expansion between the ceramic chip and the base. Usually when the power exceeds 500 watts continuous, the use of the copper tungsten base should be considered for critical applications. The cost of the copper tungsten as compared to the pure copper is significant. Therefore, it is only used in those applications where stress is a primary concern.

Figure 1

Figure 1

Figure 2

Figure 2

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