Design for in-circuit test (vintage 1994)
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The document outlines design guidelines for in-circuit testing, emphasizing the importance of component placement, board shape, edge clearance, and test pad specifications to ensure effective testing. It advises on maintaining minimum thickness, spacing between test points, and minimizing the height of components to avoid obstruction during testing. Additionally, it discusses the need for uniform component orientation and modularity to facilitate individual testing of complex products.
Design for in-circuit test (vintage 1994)
- 1. Design for In-Circuit Test Advisor DICTADICTA Rules to be included in phase 1 of the DICTA system Click mouse button to begin RF 1994
- 2. Component Mounting • Preferably, all components will be on the top side of the circuit board • Chip resistors and other small components can be placed on the secondary side of the board, but they must be located away from test pads • Any flying wires should be located on the top side of the PCB, away from test probes best - all components on one side of the PCB moderate - passives only on underside worst - both sides populated with ICs
- 3. Board Shape • To facilitate sealing for vacuum fixturing, boards should have straight sides and no internal cut-outs • Any cut-outs must be surrounded by an area clear of all obstructions. Bad shapeLess good shape Good shape
- 4. Edge Clearance • An area around the board perimeter should be free of components, test locations and other features • This should extend for at least 0.100, and preferably 0.200 inches from any edges or cut-outs Clamping or sealing the board edge becomes difficult
- 5. Tooling Hole Clearance • The clear area around tooling holes should extend for 0.375 inches
- 6. Locating Tooling Holes • Tooling holes should be provided on at least two opposite corners • If space allows, a tooling hole on a third corner will improve accuracy • Holes should be offset so the board cannot be placed in a fixture the wrong way round • All tooling holes must be unplated • Minimum diameter is 0.125 inches
- 7. Board Thickness • To avoid distortion during testing, the board should have a minimum thickness of 0.062 inches
- 8. Board Thickness • To avoid distortion during testing, the board should have a minimum thickness of 0.062 inches
- 9. Board Thickness • Thin board distorted during probing...
- 10. Board Thickness • Thin board distorted during probing...
- 11. Board Thickness • Thin board distorted during probing...
- 12. Board Thickness • Thin board distorted during probing...
- 13. Board Thickness • Thin board distorted during probing...
- 14. Board Thickness • Thin board distorted during probing...
- 15. Board Thickness • Thin board distorted during probing...
- 16. Via Holes • To ensure a reliable vacuum seal between the assembled PCB and the test fixture, via holes should be of sufficient diameter (0.062 inches or more) so they will fill during flow soldering. Likely to fill Unlikely to fill
- 17. Component Height • Components on the bottom side of the board must not obstruct the operation of the bed-of-nails fixture • It is best if components have heights of less than 0.160 inches • No components with heights greater than 0.360 inches should be mounted on the bottom of the board
- 18. Component Height • Components on the bottom side of the board must not obstruct the operation of the bed-of-nails fixture • It is best if components have heights of less than 0.160 inches • No components with heights greater than 0.360 inches should be mounted on the bottom of the board Cut-out in top plate required Recess in vacuum well required Testability unimpared
- 19. 60 mil Component / Test Land Spacing • The space between the centre of a test access point and the edges of any adjacent components must exceed 0.060 inches • This distance must be increased to 0.200 inches where the height of adjacent components exceeds 0.160 inches 200 mil
- 20. Test Land Size • Test lands should be as large as possible to ensure reliable probing • Recommended size is greater than 0.060 inches • Minimum size is 0.035 inches for a bed-of-nails type fixture • If the PCB requires two- sided probing, the minimum size for test lands on the top side is 0.040 because probing here is less accurate
- 21. Test Land Size • Test lands should be as large as possible to ensure reliable probing • Recommended size is greater than 0.060 inches • Minimum size is 0.035 inches for a bed-of-nails type fixture • If the PCB requires two- sided probing, the minimum size for test lands on the top side is 0.040 because probing here is less accurate
- 22. Test Land Size • Test lands should be as large as possible to ensure reliable probing • Recommended size is greater than 0.060 inches • Minimum size is 0.035 inches for a bed-of-nails type fixture • If the PCB requires two- sided probing, the minimum size for test lands on the top side is 0.040 because probing here is less accurate
- 23. Test Land Size • Test lands should be as large as possible to ensure reliable probing • Recommended size is greater than 0.060 inches • Minimum size is 0.035 inches for a bed-of-nails type fixture • If the PCB requires two- sided probing, the minimum size for test lands on the top side is 0.040 because probing here is less accurate
- 24. Test Land Size • Test lands should be as large as possible to ensure reliable probing • Recommended size is greater than 0.060 inches • Minimum size is 0.035 inches for a bed-of-nails type fixture • If the PCB requires two- sided probing, the minimum size for test lands on the top side is 0.040 because probing here is less accurate
- 25. Test Land Size • Test lands should be as large as possible to ensure reliable probing • Recommended size is greater than 0.060 inches • Minimum size is 0.035 inches for a bed-of-nails type fixture • If the PCB requires two- sided probing, the minimum size for test lands on the top side is 0.040 because probing here is less accurate Small test pads may well be missed as probes wear
- 26. Land Spacing • Test access points should be spaced with 0.100 inches between centres • This can be reduced to 0.075 or even 0.050 where necessary • The number of probes at smaller pitches should be kept to a minimum as these are less accurate
- 27. End of phase 1 rules Other information to be included in the multimedia design advisory system follows... Click mouse button to begin Click mouse button to continue
- 28. Board Probing • If possible the board should be probed from one side only
- 29. Board Probing • If probing from both sides of the board is necessary it will be found that probing accuracy is reduced on the top side • The location of tall components may also make testing difficult.
- 30. Board Probing • If probing from both sides of the board is necessary it will be found that probing accuracy is reduced on the top side • The location of tall components may also make testing difficult.
- 31. Board Probing • If probing from both sides of the board is necessary it will be found that probing accuracy is reduced on the top side • The location of tall components may also make testing difficult.
- 32. Board Probing • If probing from both sides of the board is necessary it will be found that probing accuracy is reduced on the top side • The location of tall components may also make testing difficult.
- 33. Board Probing • If probing from both sides of the board is necessary it will be found that probing accuracy is reduced on the top side • The location of tall components may also make testing difficult.
- 34. Board Probing • If probing from both sides of the board is necessary it will be found that probing accuracy is reduced on the top side • The location of tall components may also make testing difficult.
- 35. Component Orientation • All packages of the same style should have the same orientation so that time will not be wasted trying to identify pins during manual testing • Clear, permanent marking of pin numbering for each component is also necessary 1 14
- 36. Probing Components • Avoid probing the leads of the components • Probing component leads can mask problems with bad solder joints • Test pads should be included in the design instead
- 37. Probing Components • Avoid probing the leads of the components • Probing component leads can mask problems with bad solder joints • Test pads should be included in the design instead joint closed by probe
- 38. Probing Components • Avoid probing the leads of the components • Probing component leads can mask problems with bad solder joints • Test pads should be included in the design instead joint closed by probe
- 39. Probing Components • Avoid probing the leads of the components • Probing component leads can mask problems with bad solder joints • Test pads should be included in the design instead joint closed by probe
- 40. Test Land Geometry • Square test pads offer a greater area to hit so the testing process is more reliable Square pad offers 27% greater contact area.
- 41. Test Land Geometry • Solder on test pads may make probing difficult • Mounting pads and test pads should be separated to prevent solder flowing onto the test pad during manufacture • This also ensures the test probe will not strike a component skewed during placement or reflow Good Bad
- 42. Edge Connectors • In terms of testabiity, the best design for testing would achieve all the necessary contacts for testing at the edge connectors
- 43. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 44. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 45. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 46. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 47. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 48. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 49. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 50. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 51. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 52. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 53. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 54. Modularity • Ideally, complex products will be split into functional modules which can each be tested individually
- 55. Test Probes • Available in a variety of sizes and head configurations • Larger probes have a longer reach but may not be practical in fine pitch applications plunger wire wrap connection spring barrel fixture head
- 56. Test Probes • Available in a variety of sizes and head configurations. • Larger probes have a longer reach but may not be practical in fine pitch applications.
- 57. Test Probes • Available in a variety of sizes and head configurations. • Larger probes have a longer reach but may not be practical in fine pitch applications.
- 58. Test Probes • Available in a variety of sizes and head configurations. • Larger probes have a longer reach but may not be practical in fine pitch applications.
- 59. Test Probes • Available in a variety of sizes and head configurations. • Larger probes have a longer reach but may not be practical in fine pitch applications.
- 60. Test Probes • Available in a variety of sizes and head configurations. • Larger probes have a longer reach but may not be practical in fine pitch applications.
- 61. Test Probes • Available in a variety of sizes and head configurations. • Larger probes have a longer reach but may not be practical in fine pitch applications.
- 62. Test Probes • Available in a variety of sizes and head configurations. • Larger probes have a longer reach but may not be practical in fine pitch applications.
- 63. Test Probes • Available in a variety of sizes and head configurations. • Larger probes have a longer reach but may not be practical in fine pitch applications.
- 64. Test Probes • A large probe should be used where possible for better electrical contact and improved fixture reliability. • Smaller probes must be used where the test pads are closely packed or access is a problem.
- 65. Design for In-Circuit Test Advisor DICTADICTA End of slideshow. Click mouse button to restart.