Medical devices are shrinking rapidly while becoming more complex. Sensors, processors, optics, and connectivity are now routinely packed into form factors that would have been impractical just a decade ago. While this miniaturization unlocks new clinical value, it also exposes a persistent design challenge: many of the materials still being specified were developed for an earlier era of electronics.
Adhesives, substrates, coatings, and encapsulants that worked well for rigid circuit boards and macro-scale assemblies often fail when applied to today’s highly integrated, tight-tolerance medical devices. If device developers and their manufacturing partners continue to use yesterday’s materials, the risks could be lower yield, reduced device reliability, and painful redesigns at production and scale-up stages.
Understanding how material choices affect manufacturability is now a key responsibility of medical device designers. The following factors underscore why materials from past electronics eras fall short in modern medtech while highlighting what designers should consider as they make their material choices going forward.
Why Legacy Electronics Materials Are a Poor Fit for Modern Medtech
Traditional electronics materials were optimized for relatively static environments: rigid boards, predictable thermal cycles, and minimal mechanical motion. Today’s miniaturized medical devices rarely operate under those assumptions, because they often include:
- Thin or flexible substrates.
- Mixed materials with dissimilar thermal behavior.
- Motion, vibration, and/or repeated flexing.
- Sensitive sensors, optics, and/or surface chemistries.
- Long operational lifetimes under biological exposures.
Designers should recognize that materials that look acceptable on a datasheet can behave very differently during real manufacturing conditions and/or months later when they are in actual use.
Compliant Adhesives Selections and Proper Applications
As form factors shrink, adhesives increasingly replace mechanical fasteners and even solder joints. Designers rely on them for structural support, electrical insulation, thermal conduction, optical clarity, or damping. However, many failures traced to adhesives are not due to chemistry alone but often stem from interactions with the materials in the rest of the stack.
Key manufacturability considerations include:
- Cure temperature and profile. Even “low-temperature” cures can warp thin substrates or degrade sensitive components.
- Modulus and compliance. Rigid adhesives may introduce stress as assemblies cool, leading to micro-cracking or delamination.
- Shrinkage during cure. Volumetric changes can pull components out of alignment, especially in fine-pitch or optical assemblies.
- Process window sensitivity. Small variations in mix ratio, dispense volume, or cure time can dramatically affect production timelines and production at volume.
Since process variation will be inevitable, designers should work closely with their manufacturing partner to identify and evaluate adhesives not only for their end-use properties, but for how they will behave during assembly, rework, and thermal cycling. An experienced contract development and manufacturing organization (CDMO) will be familiar with the latest adhesives coming on the market and how they are working (or not) and can provide manufacturing feedback and insights about how materials selected by the designer will perform at all stages of production.
Low-CTE Substrates: Solving One Problem, Creating Another
As device integration density increases, controlling thermal expansion becomes even more critical during production. Designers specify low coefficient of thermal expansion (CTE) substrates to improve alignment stability or protect sensitive components, but low-CTE materials introduce their own challenges including:
- Their increased stiffness can cause and transfer stresses elsewhere within the assembly.
- If mismatched, CTE differences between substrate, adhesive, and components may create latent reliability failures.
- Some low-CTE materials are more difficult to process, drill, or metallize consistently.
Low CTE substrates can still be used, but an experienced manufacturer knows how to balance their thermal behavior across the full stack of materials and components. Manufacturers should be proactive in helping designers evaluate how substrates interact together with adhesives, coatings, and encapsulants, not just how they perform in isolation.
Biocompatible Coatings: Performance vs. Process Reality
Biocompatible coatings are essential for many medical devices, particularly implantables and wearables. But coatings that meet biocompatibility requirements may be incompatible with manufacturing realities. Some common pitfalls to anticipate and plan for include:
- Coatings that degrade or discolor under UV exposure during inspection or cure.
- Sensitivity to humidity during storage or assembly.
- Thickness variation that interferes with fine-pitch interconnects.
- Limited rework tolerance once applied.
From a manufacturability standpoint, coatings must be evaluated not only for when they are applied in the process flow, but also for how they interact with downstream production steps and how their variability may affect yield. Consistent and inspectable coatings are essential to their overall, long-term performance and robust device performance.
Assembly Physics: When Materials Drive Yield
As devices get smaller, assembly physics often become the dominant yield driver. Flatness, coplanarity, and topography are influenced directly by material choices.
- Thin substrates may wrinkle or warp during thermal processing leading to placement variation.
- Adhesive thickness variation can tilt components enough to cause open or marginal connections.
- Coating buildup can interfere with solder wetting or wire bonding causing connection issues.
In high-density assemblies, even a few microns of variation can determine manufacturing success or failure. Designers should treat material-driven assembly physics as design inputs, not downstream manufacturing issues. Questions designers should ask early:
- Will my chosen substrates remain flat through printing, placement, and reflow?
- Does my material stack support consistent fixturing?
- Can inspection reliably detect material-induced defects?
Making a Smart Decision on Outsourced Production
Many material choices appear acceptable during early prototyping, but cause problems during production scale-up. When the manufacturing of the product is outsourced, material behavior is amplified by:
- Material lot-to-lot variations and supplier lead-time volatility.
- Environmental differences across facilities.
- Statistical exposure of low-probability failure modes.
Designers need to work closely with their manufacturing partner to assess whether materials:
- Have stable supply chains.
- Tolerate process variation.
- Can be validated and controlled under ISO 13485 systems.
- Will remain robust across design revisions.
Materials that cannot scale predictably can quietly become the highest risk in a program. The most reliable medical devices are designed by taking a systems-level view of the material options. Rather than specifying adhesives, substrates, and coatings independently and in isolation, successful teams evaluate how materials interact across assembly, test, and lifecycle, with an experience manufacturing partner. Material behavior should be validated through small builds, measurement, and iteration, before tolerances and processes are locked in.
Material choices that once worked for traditional electronics often fail in modern medical devices, not because they are poor materials but because the devices themselves have changed dramatically. Miniaturization, integration, and biological interaction demand materials that are compliant, stable, and manufacturable under real production conditions. Designers who account for assembly physics, process variability, and scaling realities early are far more likely to deliver devices that succeed beyond the prototype stage.
This article was written by Dave Fromm, PhD, Chief Operating Officer at Promex Industries, Santa Clara, CA, where he leads operations, engineering, and advanced microelectronics manufacturing programs for medical device and biotechnology customers. He has extensive experience in materials selection, heterogeneous integration, and process development for highly miniaturized, sensor-driven medical devices. For more information, visit here .
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