With the growing popularity of electronic wearables and advances in medical diagnostic equipment, silicone molders are seeing an increased demand for parts molded onto electronic substrates. There are many additional considerations that a molder must be wary of when taking on an electronics over-molding project. We’ve highlighted three of the most important considerations in this post.
1. First, when designing a part, be mindful of the dimensions. Allow enough clearance to avoid damaging the substrate, while simultaneously shutting-off on the substrate to prevent overflow of material onto unwanted areas. This can be something of a delicate balance and will likely be different, based on part geometry and material used.
2. Secondly, when over-molding onto electronics, be mindful of temperature restrictions. For some electronic devices, there are components that have a lower operating temperature range than what is ideal for silicone over-molding (125°C – 175°C). Typically, this is true of battery’s capacitors. The normal operating range for most capacitors is -30°C to 125°C with nominal voltage ratings for a working temperature to be no greater than 70°C for plastic capacitors. If possible, it is best to avoid these components when over-molding electronics with LSR.
3. The last secret to over-molding electronics is surface compatibility to improve adhesion to the substrate. When two materials are chemically dissimilar, certain options are available to improve bonding:
It is always important to make sure that the substrate is clean prior to molding.
Mechanical surface preparation; such as roughening via sanding and grit-blasting, can produce good adhesion. For further improved bond strength creating undercuts or thru-holes in the substrate.
Chemical surface preparation; such as primers or other adhesion promoters, can be purchased with the suppliers of the liquid silicone such as Shin-Etsu and Wacker Silicones.
Another type of surface modification process is applying plasma to change the surface tendencies of polymer. Plasma is compressed energized gas that is applied onto the polymer molecules to break up some of the bonds. When some of the molecules are broken apart, the surface of the material will create available binding sites. Atoms from the silicone material are then allowed to come in and fill up these binding sites.
Corona discharge works very similarly to plasma treatment, but differs in that it uses an electrical arc to free up the bonding sights instead of gas and flame. Due to this corona treatment is also an effective means to improve adhesion with metallic substrates.
Every part design poses the same initial question, “what is my design intent?” There are many decisions to be made when designing a silicone part. Have you considered the following questions before finalizing your part design or requesting a quote?
Is your material compatible with the part’s intended function? Different grades of silicone are processed in different level controlled environments; the higher the grade (more pure) the more stringent controlled environment is used. Some silicone producers will certify every batch of silicone that they manufacture. Medical device companies will require lot traceability, which at Albright goes back to the material supplier. There are many silicones available that are suitable for contact with the human body. There are also grades available for short and long term implants. Silicone is a key material to the medical industry with many applications.
Will colorant or additives need to be mixed in to your material? Some silicone can be mixed with other materials; such as colorants. Other additives available include barium sulfate, tungsten and titanium dioxide, which are all used so that silicone parts can be detected in x-rays or other medical operations.
What durometer material would you like? Silicones are available in multiple durometers depending on the strength your design will need. If your durometer is too soft the part will feel very sticky. If you want a very high durometer your part will feel glass like.
Will you be overmolding a silicone part? Overmolding takes a bit of practice to find out which materials adhere best to one another. R&D hours are normally charged to cover the development of an overmolding process, which involves molding to a substrate.
What tolerance will allow your part to function correctly? Silicone is very deformable and generally tolerances are over specified. Tighter tolerances lead to more expensive molds and parts. To stay within a reasonable cost consider following RMA A3 tolerance guidelines.
How many undercuts should you create? Undercuts create irregular parting lines and result in multiple plate tools. This will increase the cost of your mold and extend production times, increasing the cost per part.
Where will your parting lines be? Whether your parting line can be visible or not, plays a factor. Parting lines are also affected by the amount of undercuts in your design. If you can avoid undercuts, your mold will be less expensive because it will reduce the amount of time machining and reduce production cycle times.
What modifications would be acceptable without affecting the part function? After getting back your engineering samples you may need to change your design. Shrinkage can occur during the molding process. Although we scale your part for shrinkage, each project is a little different, depending on your durometer, part size and undercuts.
What is the thickest area of your part? The thickness of the silicone material plays a large part in molding cycles, particularly in the curing phase. Just remember, the thicker the part, the longer the cycle, the higher the cost. What is the volume of your part? We specialize in prototype and low-volume production molding. We are not suited for molding tens of millions of parts for pennies a piece.
How fast do you need the parts? The longer the turn around time the lower the cost will be.
Do you want an injection, compression or transfer mold tool? Depending on where your parting lines are, how many parts you need to produce and how long you have to produce these parts, can all factor in to which type of mold to build.
How much money do you want to spend per part? Depending on the amount of parts required, you may want to consider a multi-cavity tool. This may be more expensive up front while purchasing a tool, but will quickly pay off through reduced production time, which means getting your parts FASTER!
Now for some questions regarding designing your parts in silicone materials. How many iterations did it take to get your design acceptable? Avoid multiple revisions by covering all aspects before designing your parts. This will save you time and money before having to go back to the drawing board. Did you know we mix your silicone in-house for control, but also mix and provide custom materials that meet your specifications? Are you curious if silicone adheres to specific plastic or metal materials? We can experiment in our lab with primers from the major silicone suppliers and provide different surface textures to create adhesion on your parts, whether they be plastic,metals or silicone.
Looking to manufacture your design prototypes in silicone and want to know how much it will be? Send your models and information through our RFQ page. We will respond within 24 hours. If you “needed your quote yesterday,” please call Christi or Ryan at 978.466.5870. They can assist you with all of your silicone molding needs.
Join Christi, David and Ryan in Boston, Massachusetts this May at the BIOMEDevice Trade Show! The show is located at the Boston Convention & Exhibition Center at 415 Summer Street in Boston. Albright is located in Booth 700.
The exhibition hall schedule is as follows:
Wednesday, May 6th, 2015 10 AM to 4 PM
Thursday, May 7th, 2015 10 AM to 4 PM
Albright will be exhibiting our silicone prototyping and production molding solutions to attendees in Booth 700, located near the entrance from registration. We are currently offering free passes to our partners in the industry. Save $75.00 dollars on registration, visitBIOMEDboston/Badgeand use the source code,AA.
We look forward to seeing you in Beautiful Boston next month. Stop by Booth 700 for a visit and learn about the latest at Albright Technologies and the medical silicone industry!
Check out Albright’s latest video and take a virtual tour of the company, while learning about the company’s manufacturing offerings. The video covers many of Albright’s in-house capabilities, including:
• Full silicone material selection from major silicone suppliers: LSR, HCR, RTV, HTV
• Prototyping AND Production
• ISO 13485 certified
• ISO 7 Clean Room, hard-walled. High capacity, HEPA-filtered air-handlers
• Clean Room processes: Material prep, molding, post-processing and inspection
• Implantable parts, both long and short-term applications
• Complex over-molds, especially dissimilar substrates and electronics
• Very large and very small parts: We micromold to sub-mm features
• In-house tooling
• Liquid injection molding
• Compression molding
• Transfer molding
Implantable silicone materials can be loaded with Barium (BaSO4) for future radiological detection purposes. Both restricted (29 days or less) and unrestricted (29 days and beyond) silicone materials can be loaded with BaSO4. This allows for the silicone part to be detected in future X-Rays and CT Scans.
Typically, the silicone material is loaded with a certain percentage of BaSO4. The loading percentage will depend on the level of contrast needed for the area of the body being viewed. Another common use of Barium loading has been in clinical trials and finished devices for failure detection and assessment since a part failure may be visible. Many of the major silicone suppliers provide Barium loaded materials today in the two implantable grades of silicone. While it is most common for the unrestricted silicone materials to be loaded, some of the restricted grades are as well.
Barium loading of silicone materials is common for the following applications:
4. Toe joints
5. Markers overmolded in silicone to detect and determine placement of devices
Now it is time for some questions for discussion on Barium loading. Have you ever manufactured BaSO4 loaded silicone parts? Did you load and mix the Barium at your company or did you purchase pre-mixed Barium silicone material? What Barium loaded silicone materials did you use?
Albright Technologies can mold your Barium loaded silicone medical devices in our ISO Class 7 hard walled controlled environment room. We can also source Barium loaded silicone material for you. If you need a custom mixed material with a certain percentage of BaSO4, Albright can mix it for you. If you are in need of a quotation for a Barium silicone related project, please visit our RFQ page here.
Many Inventors, Engineers and Project Managers believe that injection molding is the best solution for their molded silicone products. However, this is not always the case due to the many variables and constraints of manufacturing silicone parts.
First and foremost, anticipated volume is always a true concern. If you only need to mold 1 to 20,000 pieces then a compression mold is more than suitable. Secondly, do your parts have multiple undercuts or is the geometry highly complex? If so, then a compression mold may be the most viable option.
During the prototyping phase, a compression tool allows for rapid turnaround time. At Albright Technologies, we will produce a compression mold manufactured out of aluminum, along with engineering samples in 15 business days or less. Now, let’s take a look at the pros and cons of compression molding.
Parts are dimensionally to specification and made with specified materials
Short set-up times, allowing materials and colors to be changed quickly
Flexibility in mold design
Tools with multiple cavities can be made with less concern of balancing
Welding allows for tool modification
Faster mold manufacturing turnaround time
Parts with multiple undercuts can be manufactured
Mold tool cost is lower than injection
Cost of compression molding machines is low
Reduced molding process development time (day(s) not weeks)
Slower part production rates
Can be difficult to control flash
Due to the nature of our business as a silicone prototyper and low-volume production molder, compression molding is a great fit. It offers our customers a less expensive, yet rapid option (when compared to injection mold tooling) to turn their product designs into reality. We provide our customers with silicone parts that are molded from complex mold tools with many undercuts as required.
Now, it is time for some questions for discussion. Do you or your company utilize compression mold tools to manufacture silicone parts? How would you rate your overall experience with the compression molding process? How much of your molding business is processed utilizing compression molds?
When turning your design into a silicone prototype, select the World’s Premier Source for Silicone Molded Parts. Get your 3D Models quoted today, visit our RFQ page.
Visit with Christi, Jeff and Ryan in sunny and beautiful Anaheim, California this February at the MD&M West Trade Show! The show is located at the Anaheim Convention Center at 800 West Katella Avenue in Anaheim and Albright has Booth 1083.
The Exhibits schedule is as follows:
Tuesday, February 10, 2015 10 AM to 5 PM
Wednesday, February 11, 2015 10 AM to 5 PM
Thursday, February 12, 2015 10 AM to 4 PM
Albright will be exhibiting our silicone prototyping and production solutions to attendees in Booth 1083, located at the left rear of Expo Hall D. We are currently offering free passes to our partners. Save $95.00 dollars on registration, visit MDMwest.com/inviteand use the source code, invite.
We look forward to seeing you in Sunny California next month. Stop by Booth 1083 for a visit and learn about the latest at Albright Technologies and the latest in the medical silicone industry!
Silicone materials can be compounded to create materials that are both, bio-inert and fully compatible with biological systems. Medical silicones are compounded in a similar manner as general purpose silicones to obtain certain characteristics, such as durometer, elongation and tear strength. However, medical silicones undergo additional processing to remove unwanted residuals. This allows for the purest silicones to be manufactured for use in medical devices.
Silicone manufacturers have created systems to determine which materials should be used for a variety of bio-contact applications. These suppliers have created in-house certifications that are based on the positive results of a series of USP (U.S. Pharmacopeial Convention) Tests. There are six separate USP tests, from Level I to Level VI. Materials that meet each of the six tests, are often referred to as “Grade 6” materials.
To better understand the requirements of each USP test, please see the table below.
Silicone manufacturers have created several groups in which to place these various medical silicones based on their anticipated use.
Food Grade Silicones: Silicones of this group must meet USP tests, as well as FDA and USDA guidelines and criteria. Materials from this group would commonly be found in food processing equipment in the form of seals or even spatula blades.
Medical Non-Implantable: Silicones of this type do not see use inside the body. Typical applications include tubing and one-time use disposables.
Medical Short Term Implantable: These particular silicones can be implanted into the body for up to 29 days. A few applications include catheters and surgical tools.
Medical Long Term Implantable: Silicones from this group can be implanted for a period greater than 29 days. Typically these materials are used in cardiovascular implants and remain in the body until end of life.
Pharmaceutical: Silicone materials used in the pharmaceutical space, must pass all six USP tests and must be compatible with any drug coming into contact with the part. Drug delivery devices, such as punctal plugs, are typical applications in this group.
Determining which medical grade silicone material is required is based on the function and use of the medical device to be manufactured. Albright’s staff of engineers can assist you in material selection so that your medical application’s requirements are met. Please remember that although many silicone suppliers have conducted USP bio-compatibility tests on their respective materials, all finished medical devices will still need further USP testing. To learn more about medical silicone materials visit our Silicone Material page.
Before manufacturing silicone parts, it is important to select a finished durometer for the part or product that you will be molding. Depending on the requirements of the project, the silicone finished part may be near gel-like or very stiff. Durometer is a measure of hardness that is used in elastomers, polymers and rubbers. Hardness may have many definitions, but in our case with regards to Shore durometer, hardness is defined as a material’s resistance to indentation.
The Shore durometer scale was created by Albert F. Shore in the 1920’s. Originally, the result was just signified by a number, for example 50 durometer. As time progressed, multiple durometer scales were created. The Shore durometer scales that are most commonly used in plastics, rubber and silicone are the A, D and 00 shore scales.
There are two main differences amongst these scales. First, the configuration of the indenter that is pressed into the material is different with each scale. Second, the hardness range is different with each of the three scales. The Shore 00 Scale measures rubbers and gels that are ultra soft. The Shore A Scale measures rubbers that range from soft and flexible to hard with almost no flexibility. The Shore D Scale measures the hardness of hard rubbers and hard plastics.
Below is a table of common finished products and their respective durometers. Here at Albright, we use the Shore A scale to quantify our molded silicone durometers. The Shore A scale ranges from 0 to 100. An example of a “0” durometer Shore A silicone molded part would be a very soft shoe insole. Near the opposite end of the scale, an example of an “80” durometer Shore A silicone molded part would be an o-ring seal or a stiff silicone kitchen spatula. Every day, Albright molds products in materials that range in finshed durometer from 10 to 80 on the Shore A Scale.
What materials and durometers have you molded parts in? What durometer Shore scale do your materials come in? How do you determine what durometer of material to use?
Please remember that the durometer selected will be based on the requirements of your project. If you need assistance determining a durometer for your next silicone project, Albright engineers and technical staff are here to help. In addition, we can provide samples of silicone in various Shore A durometers. Want samples of silicone durometers? Visit our free durometer sample page on the Albright web site.