This one is an oldie, so please excuse the visual style. It comes from the first year of my PhD studies, 1994. The guidelines shown may still be of use to somebody working in printed circuit board (PCB) design. IT’S PROBABLY BEST DOWNLOADED since it's meant to run as a rolling slideshow, and it achieves a crude form of animations via multiple slides... File translation courtesy of Zamzar.com, which allowed me to salvage this very old file, and make it available. For the PhD thesis itself (1999), see http://usir.salford.ac.uk/34320/

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
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