Customer Background and Project Overview
The customer in this case study is a mid-sized medical device OEM specializing in in-vitro diagnostic (IVD) analyzers used in hospital labs and high-volume testing centers.
Their new generation bench-top analyzer required a modern, easy-to-clean front panel interface with a membrane keypad and several status indicators, all packaged under a single FDA-compliant graphic overlay.
The project goals were to improve infection control, reduce cleaning-related damage seen on the previous model, and ensure that the interface would support regulatory submissions in major markets.
Regulatory and Design Requirements
Because the device would be marketed as a regulated medical product, the overlay design had to support compliance with FDA expectations for labeling, usability, and cleanability.
The OEM provided a consolidated list of requirements covering not only regulatory considerations but also practical use in busy clinical environments.
| Requirement Category | Key Requirements | Implications for Overlay Design |
|---|---|---|
| Regulatory Labeling | Symbols and text must remain legible over device life; critical warnings cannot fade or be removed by cleaning. | Use subsurface printing and lightfast inks; prioritize contrast and font size for all safety-related legends. |
| Cleaning and Disinfection | Withstand daily cleaning with alcohol-based and quaternary ammonium disinfectants without cracking, softening, or discoloration. | Select chemically resistant polyester films and coatings; validate through wipe and soak testing with customer's actual disinfectants. |
| Usability and Human Factors | Clear grouping of controls, intuitive icons, and tactile feedback to support gloved operation and reduce use errors. | Design a logical keypad layout with embossed keys, clear iconography, and high-contrast legends. |
| Environmental Conditions | Operate reliably in 15–30°C lab environments with moderate humidity and occasional splashes around sample loading areas. | Ensure adequate sealing around cut-outs and edges; specify an adhesive and gasket system suitable for light splash zones. |
| Documentation and Traceability | Overlay materials and processes must be documented for design history file and future audits. | Provide material data sheets, process flow, and test reports to support the OEM's design documentation. |
These combined requirements framed the scope of work for the overlay design and highlighted the need for careful material selection and evidence-based testing.
Overlay Design Concept and Workflow
The design process began with a review of the OEM's industrial design concept and human factors inputs, followed by a series of collaborative iterations on the overlay layout and interaction details.
The goal was to preserve the visual identity of the new analyzer while ensuring that all key functions were easy to locate and operate with gloved hands.
- Information Architecture: Controls were grouped into three zones: routine operation keys, sample handling functions, and system settings, each with distinct visual cues.
- Color Coding: A conservative color palette was used, with a primary neutral background and limited accent colors for start, stop, and alarm-related keys.
- Tactile Feedback: Embossed keys were specified over the most frequently used functions, combined with metal dome switches to provide a crisp, repeatable click.
- Display Integration: A clear window was defined over the LCD area with an anti-glare finish to minimize reflections in brightly lit labs.
Throughout the design phase, digital mockups were supplemented with printed prototypes that the OEM's usability team evaluated with lab technicians for clarity and ease of use.
Material Selection and Stack-Up
Given the stringent cleaning requirements and need for long-term legend durability, a chemically resistant polyester overlay construction was chosen over polycarbonate.
The final stack-up balanced cleanability, actuation feel, and optical performance for the display window.
| Layer | Material / Specification | Function | Design Considerations |
|---|---|---|---|
| Top Surface | Hard-coated polyester, matte finish | Provides scratch, abrasion, and chemical resistance with low glare. | Matte surface reduces reflections; hard coat tested with hospital disinfectants. |
| Graphic Layer | Subsurface printed medical-grade inks | Presents legends, icons, and color coding protected beneath the film. | Inks selected for lightfastness and chemical resistance; critical text sized for readability. |
| Embossed Key Areas | Formed polyester domes over switch positions | Creates raised keys to guide the operator's finger and improve tactile feedback. | Emboss height tuned to maintain film integrity while achieving clear tactile response. |
| Adhesive Layer | Medical-grade acrylic adhesive, die-cut with continuous perimeter | Bonds overlay to the plastic front housing and contributes to splash resistance. | Adhesive chosen for compatibility with the housing resin and cleaning chemicals. |
| Display Window | Clear hard-coated polyester, anti-glare treatment | Protects LCD display while maintaining optical clarity and reducing reflections. | Window area kept free of emboss and legends; thickness optimized for clarity and flatness. |
By documenting each layer and its performance role, the stack-up could be clearly described in the OEM's design history file and future supplier qualification documents.
Manufacturing Challenges and Solutions
During pilot production, two main manufacturing challenges surfaced: maintaining consistent emboss height across the keypad and preventing tiny bubbles in the adhesive layer around the display window.
Addressing these issues early ensured stable quality before ramping up to higher production volumes.
- Emboss Consistency: Initial samples showed slight variation in key height due to temperature fluctuations during forming. The process window for emboss temperature and dwell time was tightened, and additional in-process inspections were added.
- Adhesive Bubbles: Small trapped air pockets appeared near the edges of the display window cut-out. Tooling was adjusted to add micro-vents in the adhesive pattern and optimize lamination pressure and speed.
- Color Tolerance: The customer's brand guidelines required tight color matching for the front panel. A dedicated color approval process with drawdowns and spectrophotometer checks was implemented.
Once these process adjustments were locked in, the OEM approved the revised samples for use in design verification builds and subsequent clinical evaluation units.
Testing, Validation, and FDA Compliance Support
To support the OEM's regulatory submission and risk management activities, a focused test plan was executed on overlay samples and assembled front panels.
The test results, along with material declarations, were provided as part of the documentation package for the OEM's design history file.
| Test Type | Objective | Key Parameters | Outcome |
|---|---|---|---|
| Chemical Resistance (Cleaning) | Verify no cracking, discoloration, or loss of adhesion after repeated disinfection. | Simulated 3 years of daily cleaning with customer-specified alcohol and quaternary ammonium wipes. | No visible damage; legends remained legible; adhesion unchanged. |
| Abrasion and Scratch Testing | Assess durability of hard coat under routine use and cleaning. | Taber abrasion and pencil hardness, plus manual rub tests with lint-free wipes. | Only minor gloss change within acceptable limits; no loss of critical legends. |
| Key Life and Tactile Performance | Confirm that embossed keys and domes retain feel and function over time. | Mechanical cycling to over 1 million actuations on high-use keys. | No functional failures; tactile response remained within the target force and travel window. |
| Environmental Aging | Evaluate performance after exposure to elevated temperature and humidity. | Accelerated aging in temperature/humidity chambers representative of storage and use conditions. | No cracking, peeling, or significant color shift observed. |
These test reports were referenced in the OEM's risk analysis and usability documentation, helping demonstrate that labeling and interface elements would remain safe and effective over the device's intended life.
Final Results and Customer Outcomes
After integrating the new overlay into the analyzer design, the OEM completed design verification builds and limited clinical evaluations without any overlay-related issues reported.
Compared to the previous generation product, the customer observed fewer cosmetic complaints, improved technician feedback on usability, and greater confidence in long-term cleanability.
- Improved User Satisfaction: Laboratory staff highlighted the clear legends, tactile feedback, and reduced glare from the display window as noticeable improvements.
- Reduced Service Risk: The validated chemical resistance and adhesion performance reduced concern about overlays deteriorating in the field due to aggressive cleaning protocols.
- Regulatory Support: Material documentation and test data streamlined internal reviews and contributed to a smoother regulatory submission process.
Key Lessons for Future Medical Overlay Projects
This project illustrates how early collaboration on requirements, materials, and testing can prevent costly redesigns and delays later in the development cycle.
By treating the overlay as a critical interface component rather than a cosmetic afterthought, the OEM strengthened both usability and regulatory confidence.
- Capture cleaning protocols, disinfectant types, and usability constraints at the start of the project, not after design freeze.
- Use medically appropriate materials and coatings, and validate their performance with real chemicals and realistic cycles.
- Document the overlay stack-up, test methods, and results thoroughly so they can be referenced in risk management and regulatory files.
- Include overlay design in formal usability evaluations to ensure that layout, tactile feedback, and labeling support safe operation.