Monday, June 19, 2017

.

The aesthetic appeal of overmolded designs is probably the number one attraction. Tactile feel and functional ruggedness are significant advantages. Combined with the opportunity to improve functionality and reduce cost, this makes the approach very appealing.


Let's look at a PCB, integral to an interconnect cable, that adds functionality to an electronic design. The conventional way to fabricate this product is to create a two -piece enclosure to protect and hold the PCB. Each cable, attached to either side of the device, has a discreet board-mount connector for cable attachment. In addition, a molded-on strain relief is required for the cable exit.


With an insert molding design, the cable can be soldered directly to the PCB, thereby eliminating both the material cost for the connector and labor for termination. In addition, for almost the same labor required for molding a strain relief on the cable, the entire PCB can be over-molded.

The cost advantages come from labor and material cost reductions. This combined with significantly reduced tooling cost and more rapid product introduction helps original equipment manufacturers (OEMs) to lower the initial cost of new product introduction and reduce the time required to complete the process.

Insert Molding Advantages

downlink
In general, overmolding of a PCB device is a practical approach when the size of the PCB is no larger than 4 X 4 X 1" and it has a cable attached. 

Reduced cost and lead time for tooling 
Elimination of connector for cable attachment to PCB
Improved strain relief for cable exit
Durability and mechanical resistance to shock and vibration
Environmental sealing of circuitry
Security of internal devices
Cosmetic and functional alternatives
Insert Molding Disadvantages
download

Size constraints and manufacturing process limitations are the two primary disadvantages of overmolding. When the physical size of the PCB exceeds practical limits, the injection molding forces necessary to complete the mold cycle begin to cause mechanical failure of an unprotected board. 

Also, a sizeable increase in wall thickness is required for an internal clamshell. This adds weight to the device and creates the need for larger capacity injection molding equipment that is not typically used in the cable assembly overmold industry.

Process limitations, essentially the need to have the final assembly point be at the cable assembly company, may affect outsource plans. Considerations when outsourcing these types of designs are important, and there is a substantial learning curve for consistent overmolding design and execution.