Flexible PCB

1. What is the minimum line width/spacing of flexible PCB?

Conventional: 30μm/30μm; advanced process: 12μm/12μm (IPC-2223 standard)
2. How many times can flexible boards withstand bending?

Polyester substrate: ~100,000 times; polyimide substrate: ≥1,000,000 times
3. What is the operating temperature range of flexible PCB?

Polyimide substrate: -196℃ to +260℃; polyester substrate: -55℃ to +150℃
4. How to calculate the bending radius of flexible boards?

General: R≥3×board thickness; special applications: R=1.5×board thickness
5. What is the water absorption rate of flexible PCB?

Polyimide: ＜0.5%; polyester: ~1.5%
6. What are the common flexible board substrates?

Polyimide (PI), polyester (PET), liquid crystal polymer (LCP)
7. What is the dielectric constant of flexible boards?

Polyimide: εr≈3.5; PET: εr≈3.2
8. How to prevent flexible board delamination?

Control lamination temperature profile; polyimide lamination: 280-320℃
9. What are the specifications for flexible board copper foil thickness?

Common: 18μm, 35μm, 70μm; minimum: 9μm
10. What is the maximum current density flexible PCB can withstand?

18μm copper foil: ~20A/mm²
11. How to test the bending performance of flexible boards?

Cycle bending test per ASTM D2176 standard
12. What are the surface treatment methods for flexible boards?

Electroless nickel immersion gold (ENIG), immersion tin, OSP; ENIG: Ni 3-5μm, Au 0.05-0.1μm
13. What is the suitable SMT soldering temperature for flexible boards?

Reflow peak temperature: polyimide substrate ≤260℃; PET substrate ≤230℃
14. How to design the reinforcement area of flexible boards?

Reinforcement thickness: 1.5-2×flexible board thickness; rounded edges required
15. What is the thickness of the solder mask for flexible PCB?

Conventional: 15-30μm; special requirements: up to 50μm
16. Can flexible boards be processed with blind/buried vias?

Yes; minimum blind via diameter: 0.15mm, aspect ratio≤3:1
17. How to choose between polyimide and polyester?

Polyimide for high-temperature and high-bending requirements; polyester for cost-sensitive applications
18. What are the storage conditions for flexible boards?

Humidity＜60%, temperature 20-25℃, shelf life 6-12 months
19. How to solve flexible board warpage issues?

Add balance layer design; lamination pressure: 3-5MPa
20. What is the minimum via size for flexible PCB?

Conventional: 0.3mm; advanced process: 0.1mm
21. What is the peel strength standard for flexible boards?

IPC standard: ≥1.5N/mm (18μm copper foil)
22. Can flexible boards be used with wave soldering?

Not recommended; reflow soldering or selective wave soldering is suggested
23. How to achieve EMI shielding for flexible boards?

Copper/nickel plating shielding layer; shielding effectiveness＞60dB
24. What is the dielectric loss tangent of flexible boards?

Polyimide: tanδ≈0.003; PET: tanδ≈0.01
25. What is the maximum mechanical stress bearing capacity of flexible PCB?

Tensile strength: polyimide≥150MPa, PET≥100MPa
26. How to prevent flexible board fracture at bending points?

Arc transition design; copper foil etching with 0.05mm margin
27. What is the flame retardant rating of flexible boards?

Polyimide: UL94 V-0; PET: UL94 HB
28. Can flexible boards be double-sided assembled?

Yes, with attention to reinforcement design and soldering sequence
29. What is the minimum character height for flexible PCB?

Conventional: 0.15mm; fine process: 0.1mm
30. How to measure the impedance of flexible boards?

Network analyzer; characteristic impedance control accuracy±5Ω
31. What is the maximum coefficient of thermal expansion for flexible boards?

Polyimide: X/Y axis≈15ppm/℃, Z axis≈70ppm/℃
32. What is the bonding tolerance of flexible boards?

Interlayer registration accuracy≤50μm
33. How to solve signal delay issues in flexible boards?

Control trace length; use differential pair design
34. What are the influencing factors of flexible PCB flex life?

Substrate type, copper foil thickness, bending radius, ambient temperature
35. What is the electroless copper plating thickness for flexible boards?

Through-hole copper plating thickness≥25μm
36. Can flexible boards perform 3D stereoscopic bending?

Yes, but step-by-step forming required; each bending angle≤90°
37. What is the salt spray test standard for flexible boards?

ASTM B117; no corrosion after 24 hours
38. What is the minimum pad size for flexible PCB?

0.3mm (0.1mm via), 0.5mm (0.3mm via)
39. How to improve the heat dissipation performance of flexible boards?

Add thermally conductive copper foil layer; thermal conductivity up to 150W/mK
40. What is the withstand voltage of flexible boards?

Conventional insulation withstand voltage≥500V; special design up to 1500V
41. What is the minimum curling radius limit of flexible boards?

Polyimide minimum curling radius: R=1mm (0.1mm thickness)
42. How to prevent blistering during flexible board soldering?

Preheating temperature 80-120℃; soldering time＜3s
43. What is the surface roughness requirement for flexible PCB?

Ra≤1.5μm (ENIG surface)
44. What is the solderability test standard for flexible boards?

JIS Z3198; wetting time＜3s
45. What is the dynamic bending test speed for flexible boards?

Conventional: 5-10 cycles per minute
46. How to design the folding area of flexible boards?

Hollow grid design; retain 20% substrate support
47. What is the maximum assembly density of flexible PCB?

Can achieve 0201 component placement; minimum spacing 0.3mm
48. What are the moisture-proof treatment methods for flexible boards?

Vacuum packaging + desiccant; humidity indicator card＜10%
49. What is the lamination time control for flexible boards?

Polyimide lamination time: 30-60 minutes
50. What is the flex fatigue test cycle for flexible boards?

1,000,000 cycles; performance inspection every 100,000 cycles
51. What is the minimum line width design limit for flexible PCB?

Theoretical limit: 10μm (laser direct imaging technology required)
52. What are the curing conditions for flexible board solder mask ink?

150℃ for 60 minutes or 180℃ for 30 minutes
53. Does the dielectric constant of flexible boards change with frequency?

Polyimide: εr=3.5 at 1GHz, εr=3.2 at 10GHz
54. How to test the insulation resistance of flexible boards?

500V megohmmeter; resistance≥10¹²Ω
55. What is the maximum pressing pressure for flexible boards?

Lamination pressure is 4-6MPa (polyimide substrate)
56. What is the minimum hole diameter processing method for flexible PCBs?

Laser drilling (minimum 0.1mm), plasma etching
57. What is the copper foil peel test method for flexible boards?

IPC-TM-650 2.4.8 standard, 90° peel test
58. What is the damp heat resistance of flexible boards?

No failure after 1000 hours in 85℃/85% RH environment
59. What is the surface treatment friction resistance of flexible boards?

ENIG surface friction resistance ≥500 times (CS-10 wheel, 1000g pressure)
60. How to design the connection area of flexible boards?

Adopt rigid-flex combination design, connection area length ≥5mm
61. What is the minimum bending radius test standard for flexible PCBs?

IPC-6013, no cracking after 1000 cycles of bending
62. What is the number of repairable times for flexible boards?

Recommended ≤2 times, maximum not exceeding 3 times
63. What are the thermal stress test conditions for flexible boards?

-55℃ to +125℃ cycle 100 times, 30 minutes stay each time
64. What is the hardness of the solder mask for flexible boards?

Pencil hardness ≥3H
65. What is the flexure test angle range for flexible boards?

0-180°, focusing on 90° bending performance
66. How to solve the signal crosstalk of flexible boards?

Add shielding layer, control trace spacing ≥3 times line width
67. What is the minimum pad annular ring width for flexible PCBs?

Conventional 0.15mm, minimum 0.1mm
68. What are the process parameters for electroless nickel and gold plating on flexible boards?

Nickel deposition rate 1-2μm/h, gold deposition rate 0.02-0.05μm/h
69. What is the maximum number of layers for flexible boards?

Conventional 8 layers, maximum up to 20 layers
70. What is the impact resistance of flexible boards?

Can withstand 50g acceleration, 11ms duration impact
71. What are the bending fatigue failure modes of flexible boards?

Copper foil cracks (70%), substrate delamination (20%), connection point fracture (10%)
72. How to detect the peel strength of flexible boards?

Use a tensile testing machine at a speed of 100mm/min
73. What is the minimum character line width for flexible PCBs?

Conventional 0.05mm, fine process up to 0.03mm
74. What is the control of the lamination temperature curve for flexible boards?

Heating rate 2-3℃/min, temperature holding stage ±5℃ fluctuation
75. What is the surface treatment adhesion test for flexible boards?

3M 600 tape test, no coating peeling off
76. What are the environmental requirements for flexure testing of flexible boards?

Temperature 23±2℃, humidity 50±5%
77. How to design the stress relief structure of flexible boards?

Adopt stress relief designs such as serpentine traces and U-shaped slots
78. What is the minimum via annular ring width for flexible PCBs?

Conventional 0.15mm, minimum 0.1mm
79. What is the solvent resistance of the solder mask for flexible boards?

Wiped with acetone 10 times, no peeling off
80. What is the dynamic bending test angle for flexible boards?

Common ±90° cyclic bending
81. How to solve the thermal deformation problem of flexible boards?

Select substrates with low coefficient of thermal expansion and increase heat dissipation channels
82. What is the maximum operating humidity for flexible boards?

Long-term operating humidity ≤90% RH
83. What is the temperature coefficient of dielectric constant for flexible boards?

Polyimide △εr/△T≈-0.001/℃
84. What is the minimum line width tolerance for flexible PCBs?

±10% (conventional process), ±5% (high-precision process)
85. What are the material selections for stiffeners of flexible boards?

FR-4, polyimide stiffeners, thickness 0.1-0.5mm
86. What are the key points of design for manufacturability (DFM) of flexible boards?

Avoid sharp angles, control copper foil uniformity, optimize bending areas
87. What is the corrosion resistance of the surface treatment for flexible boards?

Salt spray test for 48 hours, no corrosion
88. What is the flexure life prediction model for flexible boards?

Coffin-Manson equation: Nf=A (Δε)^(-m)
89. How to detect the hole wall roughness of flexible boards?

Observed by scanning electron microscope (SEM), Ra≤10μm
90. What is the maximum bending frequency for flexible PCBs?

Recommended dynamic bending frequency ≤2Hz
91. What is the adhesion test method for the solder mask of flexible boards?

Cross-cut method (ISO 2409), grade 0 is qualified
92. What is the interlayer bonding force standard for flexible boards?

IPC standard requires ≥1.2N/mm
93. How to calculate the signal transmission delay of flexible boards?

Delay = trace length ×√εr×0.167 (ns/cm)
94. How to design the heat dissipation copper layer of flexible boards?

Copper layer thickness ≥70μm, open window area ≥30%
95. What is the vibration resistance of flexible boards?

Can withstand 10-2000Hz, 2g acceleration vibration
96. What is the minimum test point size for flexible PCBs?

Conventional 0.6mm, minimum 0.4mm
97. What is the surface treatment abrasion resistance test for flexible boards?

Taber abrasion test, CS-10 wheel, wear amount ＜10mg after 1000 revolutions
98. What is the selection of copper foil thickness in the bending area of flexible boards?

9μm or 12μm copper foil is recommended for the bending area
99. What is the temperature shock resistance of the solder mask for flexible boards?

-40℃ to +150℃ cycle 50 times, no cracking
100. What are the key items of design rule check (DRC) for flexible PCBs?

Line width/spacing, via size, bending radius, stiffener design

Flexible PCB

1. What is the minimum line width/spacing of flexible PCB?

2. How many times can flexible boards withstand bending?

3. What is the operating temperature range of flexible PCB?

4. How to calculate the bending radius of flexible boards?

5. What is the water absorption rate of flexible PCB?

6. What are the common flexible board substrates?

7. What is the dielectric constant of flexible boards?

8. How to prevent flexible board delamination?

9. What are the specifications for flexible board copper foil thickness?

10. What is the maximum current density flexible PCB can withstand?

11. How to test the bending performance of flexible boards?

12. What are the surface treatment methods for flexible boards?

13. What is the suitable SMT soldering temperature for flexible boards?

14. How to design the reinforcement area of flexible boards?

15. What is the thickness of the solder mask for flexible PCB?

16. Can flexible boards be processed with blind/buried vias?

17. How to choose between polyimide and polyester?

18. What are the storage conditions for flexible boards?

19. How to solve flexible board warpage issues?

20. What is the minimum via size for flexible PCB?

21. What is the peel strength standard for flexible boards?

22. Can flexible boards be used with wave soldering?

23. How to achieve EMI shielding for flexible boards?

24. What is the dielectric loss tangent of flexible boards?

25. What is the maximum mechanical stress bearing capacity of flexible PCB?

26. How to prevent flexible board fracture at bending points?

27. What is the flame retardant rating of flexible boards?

28. Can flexible boards be double-sided assembled?

29. What is the minimum character height for flexible PCB?

30. How to measure the impedance of flexible boards?

31. What is the maximum coefficient of thermal expansion for flexible boards?

32. What is the bonding tolerance of flexible boards?

33. How to solve signal delay issues in flexible boards?

34. What are the influencing factors of flexible PCB flex life?

35. What is the electroless copper plating thickness for flexible boards?

36. Can flexible boards perform 3D stereoscopic bending?

37. What is the salt spray test standard for flexible boards?

38. What is the minimum pad size for flexible PCB?

39. How to improve the heat dissipation performance of flexible boards?

40. What is the withstand voltage of flexible boards?

41. What is the minimum curling radius limit of flexible boards?

42. How to prevent blistering during flexible board soldering?

43. What is the surface roughness requirement for flexible PCB?

44. What is the solderability test standard for flexible boards?

45. What is the dynamic bending test speed for flexible boards?

46. How to design the folding area of flexible boards?

47. What is the maximum assembly density of flexible PCB?

48. What are the moisture-proof treatment methods for flexible boards?

49. What is the lamination time control for flexible boards?

50. What is the flex fatigue test cycle for flexible boards?

51. What is the minimum line width design limit for flexible PCB?

52. What are the curing conditions for flexible board solder mask ink?

53. Does the dielectric constant of flexible boards change with frequency?

54. How to test the insulation resistance of flexible boards?

55. What is the maximum pressing pressure for flexible boards?

56. What is the minimum hole diameter processing method for flexible PCBs?

57. What is the copper foil peel test method for flexible boards?

58. What is the damp heat resistance of flexible boards?

59. What is the surface treatment friction resistance of flexible boards?

60. How to design the connection area of flexible boards?

61. What is the minimum bending radius test standard for flexible PCBs?

62. What is the number of repairable times for flexible boards?

63. What are the thermal stress test conditions for flexible boards?

64. What is the hardness of the solder mask for flexible boards?

65. What is the flexure test angle range for flexible boards?

66. How to solve the signal crosstalk of flexible boards?

67. What is the minimum pad annular ring width for flexible PCBs?

68. What are the process parameters for electroless nickel and gold plating on flexible boards?

69. What is the maximum number of layers for flexible boards?

70. What is the impact resistance of flexible boards?

71. What are the bending fatigue failure modes of flexible boards?

72. How to detect the peel strength of flexible boards?

73. What is the minimum character line width for flexible PCBs?

74. What is the control of the lamination temperature curve for flexible boards?

75. What is the surface treatment adhesion test for flexible boards?

76. What are the environmental requirements for flexure testing of flexible boards?

77. How to design the stress relief structure of flexible boards?

78. What is the minimum via annular ring width for flexible PCBs?

79. What is the solvent resistance of the solder mask for flexible boards?