Polyimide PCB and FR4 printplaat are two of the most prevalent used PCB types. Though both are polymer substrates well-suited for PCBs, Polyimide and FR4 each possess their own distinct characteristics that make them more appropriate for certain settings over others. In deze blog, we explain their key differences and provide insights on how to choose between them. Laten we verder lezen.
Most FR4 boards use electrodeposited copper foils with a vertical grain structure optimized for rigid boards. Polyimides more commonly use rolled annealed copper designed specifically to withstand repeated flexion without metal fatigue or cracking. The orientation of the copper grain also matches the flexing axis for maximum durability.
FR4 is made up of epoxy resin, layers of woven fiberglass, and copper. The number of fiberglass layers determines the overall thickness. The fibers are saturated with epoxy then cured with the copper layers under heat and pressure to form the rigid board. In tegenstelling tot, polyimide boards contain only polyimide plastic polymer and copper. The polyimide is cast onto the copper foils in liquid form, then fully cured to a solid, flexible state.
The fiberglass reinforcement limits how thin FR4 can be manufactured. Common thicknesses range from 2 mils naar 125 mils. Without fiberglass, polyimides can made as thin films from 1/2 mil to 3 mils thick. This allows extremely thin, flexible constructions ideal for dynamic flexing applications.
Polyimide boards are highly flexible, which makes them suitable for applications requiring repeated bending or shaping to fit specific spaces. Their extreme flexibility allows complex geometries impossible to achieve with traditionally rigid FR4 boards. Mobility is improved and installation inside products with space constraints becomes simpler compared to FR4.
Epoxy-based FR4 absorbs very little environmental moisture, in de omgeving van 0.2-0.5% of total weight. In tegenstelling tot, polyimide can absorb up to 2% moisture by weight. This does not impact the performance of polyimide circuits, but absorbed moisture must be removed by a baking process before assembly to prevent damage from rapid steam expansion and delamination issues during soldering operations.
Polyimide has a far higher maximum operating temperature than FR4, rated for continuous use up to 300°C. It resists heat degradation better over time. This means polyimide boards survive long-term in hot environments. The thermal conductivity is also double that of standard glass-reinforced boards.
Further reading: Een uitgebreide gids voor FR4 thermische geleidbaarheid
In addition to heat performance, polyimide boards provide corrosion and chemical resistance superior to FR4. Their robust polymer matrix protects against fuels, oils, solvents for considerably longer time periods. Without susceptible components like epoxy or glass fibers, polyimide stands up to more concentrated chemical solutions without degrading.
Vibration resistance and tensile strength are significantly higher in polyimide boards. Flexibility prevents fractures from physical shocks that compromise the integrity of rigid epoxy glass boards. Polyimide better maintains mechanical and electrical reliability over thousands of bend cycles as well as continuous vibration.
The following table lists some specific data to more clearly compare the differences between FR4 PCB and Polyimide PCB:
PCB-typen Properties | FR4 printplaat | Polyimide PCB |
Warmtegeleiding | 0.25 W / mK | 0.2 W / mK |
Diëlektrische constante (Bij 1 GHz) | 4.25-4.55 | ~3.4 to 3.8 |
Afvoerfactor (Bij 1 GHz) | 0.016 | 0.003 |
Boogweerstand: | 125 sec | 143 sec |
Specific Gravity | 1.8 - 1.9 | 1.3 naar 1.4 |
Waterabsorptie | 0.2-0.5% | 1-2% |
Treksterkte | 70-90 MPa | 200-300 MPa |
Glass Transient Temperature (Tg) | 130-140° C | >250° C |
The choice between using an FR4 PCB versus a polyimide PCB depends primarily on the application and its specific requirements:
FR4 boards would be the better choice for:
Polyimide boards would be preferable for:
Know differences between flexible and rigid-flex PCB, read “Stijve flexibele printplaat vs.. Flexibele printplaat”
In essentie, choose economical FR4 for basic interconnect applications without special requirements, while polyimides serve extreme demands needing maximum physical resilience and environmental resistance.
Evaluating the contrasts between these two materials in factors like heat tolerance, duurzaamheid, and mechanical strength is key when determining the optimal selection for an electronics project based on its particular demands and operating conditions. A thoughtful analysis of application specifications alongside Polyimide and FR4’s respective property profiles allows for an informed material call that caters to the unique objectives and constraints at play. With an understanding of the tradeoffs involved, engineers can feel confident specifying the PCB-substraat that will best meet their needs and perform as intended within the target device or system.
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