Potting method

Abstract

A method of potting e.g. a stack of printed circuit boards, the method comprising applying a first potting material to selected regions of the circuit to be potted and then applying a second, different, potting material over the circuit to be potted.

Claims

1. A method of potting a circuit unit comprising a stack of two or more printed circuit boards, the method comprising: stacking the two or more printed circuit boards connected by interconnections to assemble the circuit unit; performing a first potting stage by applying a first potting material to pot selected regions of the circuit unit following assembly of the circuit unit through the stacking, wherein the selected regions include one or more printed circuit boards of a lower part of the stack or one or more interconnections of the lower part of the stack; and performing a second potting stage by applying a second, different potting material over the circuit unit and over the first potting material, wherein the first potting material has a lower density than the second potting material.

2. The method of claim 1 further comprising curing the first potting material before the second potting stage and curing the second potting material after the second potting stage.

3. The method of claim 1, wherein the first potting material is a gel-type material and the second potting material is an elastomer material.

4. A potted circuit unit comprising: a circuit unit comprising a stack of two or more printed circuit boards connect by interconnections; a first potting material applied to pot selected regions of the circuit unit after the two or more printed circuit boards are stacked to assemble the circuit unit, wherein the selected regions include one or more printed circuit boards of a lower part of the stack or one or more interconnections of the lower part of the stack; and a second, different potting material applied over the circuit unit and over the first potting material, wherein the first potting material has a lower density than the second potting material.

5. The potted circuit unit of claim 4, wherein the first potting material is a gel-type material and the second potting material is an elastomer material.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a schematic view of how the potting method of this disclosure can be used.

DETAILED DESCRIPTION

(2) FIG. 1 shows an example pcb stack 100 to be potted. In the example, the stack comprises three pcbs 1,2,3 and interconnections 10, 11, 12, which may be wires, welds, bonds or other mechanical or electrical interconnections between, to and from the pcbs. Of course any other devices, components or circuitry units can be potted according to the method.

(3) In the example, there is a desire to reduce stresses on the lower two pcbs 1,2 and on the interconnections 10, 11, 12, whilst ensuring that the stack has the required rigidity.

(4) The potting method of this disclosure involves pre-potting selected regions of the stack 100—here the lower two pcbs 1,2 and interconnections 10, 11, 12, using a first potting material 200 selected to provide some damping to these regions. The first potting material is preferably less dense than conventional potting material and may be e.g. a gel-type material. The potting of the selected regions is performed in a known manner and the first potting material is cured.

(5) The stack 100 is preferably provided in a housing 500 and the first potting material is, in examples such as that shown, poured or dispensed into the housing first to pot the selected parts of the unit. This is then cured. After curing, the housing is topped up with a second potting material. The second potting stage is performed by applying potting of the second, different potting material 300 over the top pcb 3 and over the first potting material 200 to provide a desired greater rigidity at the top of the unit which is more subject to impact etc. The second potting material is preferably denser than the first and may be e.g. a conventional silicone elastomer material. This is applied in any known manner and is cured.

(6) FIG. 1 is just one example. The method of this disclosure allows any selected regions to be pre-potted. The stresses induced on the circuit will be accommodated by the first potting material rather than the stresses being applied directly to the selected regions e.g. individual pcbs or interconnections.

(7) Depending on the unit, and whether there is clearance in the housing 500, the second potting 300 could also extend around the sides and even the bottom of the unit in the housing.

(8) As an example, the inventor has experimented with Dow Corning™ EE3200 potting for the first potting material and Sylgard™ 1700 for the second potting material, but these are just two of many possible examples.

(9) The potting method of this disclosure can find application in a wide range of industries where potting of circuitry is necessary, and where vibration damping is desirable.