Electronics Silicone Overmolding

Electronics Silicone

Silicone Rubber Overmolding

Silicone rubber overmolding is a manufacturing process that molds a layer of silicone directly onto a pre-formed base component. The pre-formed base component can include flexible circuits, PCBA, connectors, or metal substrates.

This technique leads to the creation of a single, integrated part. Essentially, it combines structural strength with silicone’s tactile, durable, and protective properties without the need for any adhesives.

Silicone rubbers can be overmolded onto thermoplastics, metals, PCBAs, and other substrates. Rubber overmolding is commonly used to absorb shock, act as a seal, provide a softer touch feel, and so on. Often, the industry usage of this technique is to separate the non-biocompatible internal components of a device using a bioinert silicone for an electronics elastomer.

One of the most common challenges in rubber overmolding is protecting the insert or the substrate as the molding process takes place. This mold has to be designed carefully to hold the insert in place under injection pressures while avoiding tight clearances that could lead to the insert getting crushed.

Dimensional variations are common within a sample lot that includes plastic parts, metal inserts, PCBAs, or other substrates. Our incoming quality control inspection team identifies parts that fit too tightly or loosely in the mold. The out-of-specification samples are quarantined before the production process even begins. While it is true that inserts can be expensive, a damaged tool is usually costlier.

Achieving the desired adhesion between the silicone and the plastic or metal substrate is critical to every electronics overmolding project. This can be accomplished through mechanical interlocking, primers, surface treatments, or self-adhesive silicone materials. We also keep inserts and substrates clean at all stages, while also avoiding any chemicals that could inhibit the silicone cure chemistry. Pre-heating the plastic and metal inserts can also be an option, as it promotes a stronger bond. However, we avoid pre-heating any materials with a low melt temperature.

Mechanical Interlocking

If you have the design freedom to modify the insert or substrate, adding undercutting features will lock and hold the silicone rubber in place mechanically. This approach is especially useful in electronics overmolding. This is due to the importance of securing components in this step. Using silicone for electronics with a mechanical interlock ensures durability and protection without the need to rely solely on chemical adhesion.

Primers

When modifying the insert design is not an option, a primer applied to the surface becomes the next best choice. Depending on the primer used, once applied, it dries in 30 minutes to 2 hours. After curing, the insert is overmolded with silicone rubber, which produces a reliable and consistent bond.

Surface Treatments

Plasma, Corona discharge, and Particulate Blasting are common surface preparation techniques used in rubber overmolding. Corona discharge is particularly effective for plastic inserts. These methods increase the surface area, and they alter the surface chemistry to enhance the bonding between the silicone and the substrate. When working with silicone for electronics, proper surface preparation becomes foundational to a strong and lasting part.

Self Adhesive Materials

Several self-adhesive liquid silicone rubber (LSR) materials bond directly to plastics without the use of primers or surface treatments. These silicone elastomers bond well with Polycarbonate (PC), Polubutylene Terepthalate (PBT), Polyethylene Sulfide (PPS), Polyether Ether Ketone (PEEK), and Nylons (PA).

Benefits of Electronics Overmolding

Electronics overmolding does more than just bond two materials together. It transforms how a device performs in the real world. When silicone for electronics is applied correctly, the finished part gains a level of environmental protection. This level of protection cannot be achieved simply by a bare circuit board or connector.

Moisture and dust ingress are among the most common causes of field failures in electronic devices, and a properly designed silicone overmolding creates a continuous seal around sensitive components. This helps the products meet IP-rated protection standards for outdoor, wearable, and industrial use.

Beyond sealing, rubber overmolding also adds meaningful shock and vibration resistance. Flexible circuits, PCBAs, and connector assemblies are frequently exposed to drops, repeated flexing, and constant vibration in the field. A silicone layer absorbs and dampens these forces before they reach the rigid substrate underneath. This further reduces the solder joint fatigue and extends the usable life of the component.

The same flexibility also allows silicone overmolded parts to flex with cables and wearable housings. This further helps the parts avoid cracking under repeated movement.

Silicone is also a reliable electrical insulator, which makes it a natural fit for protecting exposed leads, terminals, and connector interfaces from short circuits and corrosion. Because it can be molded across a wide range of durometers, the same base material can be turned from soft and cushioning to something firm and structurally supportive.

This versatility is part of why silicone overmolding has become the preferred approach for engineers who are designing the next generation of compact, connected devices.

Applications and Industries

Electronics overmolding is used wherever a device needs to survive outside a controlled environment.

Wearable technology, such as fitness trackers, smartwatches, and health monitoring patches, relies on silicone overmolds to keep sweat, water, and skin oils away from internal sensors. The overmold’s soft-touch feel also remains comfortable against the body. Medical devices use the same approach to protect sensors, cables, and handheld diagnostic equipment, often combined with biocompatible silicone grades for prolonged and direct skin contact.

Connectors and cable assemblies are another major use case. Rubber overmolding at the cable-to-connector transition point creates strain relief and a sealed boundary that prevents moisture and dust from migrating into the device through the cable jacket. Consumer electronics manufacturers apply overmolding for designing soft-touch buttons, charging ports, and housings that need to withstand daily drops and handling.

Industrial sensors and outdoor equipment often depend on overmolded silicone to survive temperature swings, washdowns, and continuous vibrations in the environment. In such situations, a traditional plastic housing alone would fail.

Across all of these applications, the underlying goal, however, remains the same. The usual objective of silicone overmolding is to combine the structural or electrical function of a rigid substrate with the protective, flexible qualities that silicone for electronics uniquely provides.

Konark

Why Konark?

At Konark, we pride ourselves on quality. Our goal is to ensure that the first silicone part and the millionth silicone part are exactly the same. We practice lean manufacturing techniques and Six Sigma quality principles. Continuous improvement drives everything we do. We design our process to meet each customer’s project requirements exactly. Be it for incoming material quality and precision tooling, or a robust and repeatable molding process.

Contact Konark Silicones today, and one of our silicone molding experts will be happy to assist you with your electronics overmolding project.

Frequently Asked Questions on Silicone Rubber Overmolding

What does the Term “Electronics Overmolding” Actually Imply?

Electronic overmolding is the process of molding silicone or rubber directly onto a flexible circuit, PCBA, connector, or metal substrate to create a single, integrated part. The overmold seals and protects the underlying component while adding shock resistance and a durable outer layer.

Can Silicone Overmolding be Used on Flexible and Ribbon Circuits?

Yes. Silicone overmolding is well-suited for flexible circuits and ribbon cable assemblies. This is because cured silicone flexes with the substrate rather than resisting its movement. This prevents delamination, cracking, and connector fatigue that rigid overmold materials would introduce. Mold design is especially critical here as it helps avoid crushing or displacing the circuit during injection.

Does Overmolding Require a Primer?

This is not always the case. Some self-adhesive liquid silicone rubbers bond directly to plastics like PC, PBT, and PEEK without a primer. For substrates that do not support self-adhesion, a primer or surface treatment is used to achieve a strong mechanical and chemical bond.

Can Silicone Rubber Overmolding Make Electronics Waterproof?

Yes. When designed with proper wall thickness and substrate preparation, a silicone overmold creates a continuous barrier against moisture and dust. This helps devices meet IP-rated protection levels for outdoor, wearable, and washdown environments.

How Does Silicone Overmolding Compare to Potting or Conformal Coating for Electronics Protection?

Potting encapsulates a component entirely in a poured compound. Alternatively, conformal coating applies a thin protective film. Silicone overmolding, by contrast, produces a precisely shaped, repeatable part with defined geometry, controlled wall thickness, and the option for soft-touch surfaces. Overmolding is generally preferred when the finished part needs to meet dimensional tolerances, carry an IP rating, or integrate ergonomic features alongside environmental protection.

Electronics Silicone Overmolding