BGA - Ball Grid Array Inspection Workshop. Bob Willis leadfreesoldering.com

Transcription

1 BGA - Ball Grid Array Inspection Workshop Bob Willis leadfreesoldering.com

2 Mixed Technology Assembly Processes Adhesive Dispensing Component Placement Adhesive Curing Turn Boar Over Conventional Insertion Wave Soldering Inspection

3 Inspection Techniques X-ray inspection procedures Optical inspection (Endscope( Endscope) Destructive mechanical testing

4 PBGA Reflow

5 Ceramic Ball Grid Array

6 Ceramic Column Grid Array

7 Chip Scale Array

8 Flip Chip Packages

9 Flip Chip Package No-flow Underfill

10 Lead-Free Ball Grid Array

11 ERSA Optical Inspection Systems

12 METCAL Optical Inspection Systems

13 Optical Inspection Systems KH Benz Kaisertech

14 Optical Inspection Systems

15 Optical Inspection Systems

16 X-Ray Inspection Systems

17 X-Ray Inspection Systems

18 Very Skilled Operator Operator under Training

19 Design & Layout

20 Design & Layout

21 Solder Mask Defined Pads

22 Design & Layout

23 BGA Wetting Indicators

24 BGA X-Ray X Assement of Rework BGA Soldered with Sn/Ag/Cu

25 BGA X-Ray X Assement of Rework BGA reworked with Sn/Ag/Cu paste

26 BGA X-Ray X Assement of Rework BGA reworked with Sn/Ag/Cu flux gel

27 Area Array Alignment Marks

34 Area Array Alignment

35 General Inspection of BGA SIZE OF BALL TERMINATIONS Ball diameter should be equal to or larger than the original ball l diameter on the BGA prior to reflow due to the addition of paste. In the case of high temperature erature lead/tin ball termination's which do not reflow there should be no change in ball size. STANDOFF HEIGHT OF BGA PACKAGE. Measure the difference in height between the board and the base of the BGA laminate on a minimum of two of the four corners. Compare the variation in height of the BGA by scanning along the length of the BGA on two sides. The height will be equal to or less than the original ball height. The stand off height will reduce due to the size of the device and its weight. Variations in height between the centre and the edges of the BGA may indicate warpage of the fibre glass device or PCB. It can also indicate voiding in the ball terminations. This is more commonly noted if all termination measurements are taken. This technique is much simpler with X-ray as it can be automated. Warpage can occur up or down in the centre area of the part. Although uncommon warpage can even be seen on ceramic packages.

36 General Inspection of BGA CHECK FOR SOLDER SHORTS Scan along two adjacent sides of a BGA using light from the opposite side of the devices. There should be no restrictions to viewing each of the termination outlines. If light is restricted short circuits may be visible under the device. Viewing two sides ensures that shorts can be seen; viewing one side only shorts can be missed. Check for complete reflow of solder paste and ball terminations on tin/lead or lead-free joints. In the case of high temperature balls on ceramic parts the ball will not become liquid. During soldering the paste will reflow and allow wetting to take place between the high temperature ball and the pad surface. There will be a distinct line between the ball and the solder at the interface. This is due to the different metal surfaces being joined. CHECKING FOR CRACKING OR POPCORNING BGA failures do occur for a variety of reasons, they may be component, onent, printed board, process or design related. On some occasions both X-ray and optical inspection can easily provide the answer and that is when other techniques must be used. Microsections, dye penetrant and acoustic scans may assist is pinpointing the root cause. The essential aspect in all analysis is the experience of the engineer

37 BGA Cracking Popcorning

42 General Inspection of BGA INSPECTION OF BALL GRID ARRAY Inspection of the solder joints should start at the centre of the BGA. This area is the most likely to be the last point to reflow during soldering. It is the most likely area to exhibit voids, non reflow or component delamination. If X-ray is being used after rework the whole area beneath the part should be scanned. All BGA termination points should be broadly circular in appearance and consistent in size. Measurement of a ball under the centre of the BGA and four outer positions could allow confirmation of complete reflow. These measurements could be compared with historical data. BGA termination pads may include a wetting indicator. If this is the case it will make solder joint inspection easier to assess. A wetting indicator is a minor change to all pad shapes or a track from the mounting pad which is left exposed. In each case the solder paste can wet away from the main pad in a controlled manner, wetting may then be confirmed by X-ray. Use of oblique angle X-ray views is ideal as it will often help the investigation of the joint interfaces by allowing a better observation of the interface, this might otherwise be obscured if the view is limited to top down.

43 BGA Reflow X-RayX

44 General Inspection Criteria Inspection Criteria The following provides a guide to inspection criteria for area array solder joints using x-ray and optical inspection. The basic criteria are provided for low and high temperature area array devices. Ball Grid Array Devices The ball termination should positioned on the centre of the land, they should not overhang the pad by more than 25%. The clearance between ball terminations after reflow should not be less than the minimum electrical clearance, ball to ball distance. There should be no evidence of solder shorting under area array devices. Stand off height will be equal or less than the original ball termination. Measurements s of stand off height during production will allow process limits to be defined for any group of devices. Solder voiding on terminations should be less than 20% of the attachment tachment area on the pad. Evidence of complete reflow of solder paste should be seen. Complete reflow of high temperature balls or columns may not be visible. Solder joints on any one device should have uniform shape and size and surface appearance which depends on the process, materials and the soldering atmosphere.

45 General Inspection of BGA Low temperature ball terminations will show evidence of complete drop of the ball and paste combining to form a ball shape appearance. High temperature balls will have a waist line/demarcation line between the reflowed solder and the ball. There should be some evidence of solder wetting under the high temperature ture balls There should be no evidence of damage to the balls or pads on either the component or printed circuit board. Variations of ball size over 15% can indicate voiding or compression sion of balls due to PCB or package warp. Where present wetting indicators should show some evidence of solder flow. The distance criteria for process control ol can be defined during production inspection. Column Grid Array Devices All columns should be located on the pads, the columns should not overhand the pad surface. Slight deflection of the columns is allowed provided d it is still positioned on the pads. There should be a solder fillet around the complete circumference of the columns. There should be some evidence of solder wetting under the high temperature columns. The solder should wet to a minimum height of (0.25mm)

46 Design & Layout Via in Pad

57 Design & Layout Through Via Mounting

58 Design & Layout Through Via Mounting

59 Profiling BGA Board Assemblies One row of balls removed to the centre

60 Profiling BGA Board Assemblies

61 Lead-Free BGA with Tin/Lead Paste BGA Reflowed, balls did not reflow BGA compressed during reflow

62 Lead-Free BGA with Tin/Lead Paste Balls have not reflowed paste has this is not clear on these images

63 Lead-Free BGA Optical Inspection Balls have not reflowed paste has this is very clear on these images

64 Lead-Free BGA Optical Inspection

65 Lead-Free BGA with Tin/Lead Paste Balls have not reflowed paste has wetted pads this is shown by the perfect circle of the x-ray image

66 Lead-Free BGA with Tin/Lead Paste Balls have not reflowed but tin/lead paste has reflowed and wetted the joints

67 Plastic Ball Grid Array

68 High Temperature Terminations

69 Ceramic Ball Grid Array

72 X-Ray Inspection BGA CGA Chip Component J Lead Gull Wing Leadless Castellation

73 X-Ray Inspection The maximum void size in any one termination will be less than 10% of that minimum solder joint dimension. In the case of multiple voids the maximum area will be less than 10%.

74 X-Ray Inspection Bellcore GR 78 The maximum void size in any one termination should not exceed 1% (by volume) on average, with a worst-case incidence of 5% in less than one joint per circuit assembly.

75 X-Ray Inspection Voids up to 24% of the pad area had no effect on reliability. They improved the reliability by 16% when compared with void free joints.

76 IPC 610D draft Inspection Criteria Plastic BGA Alignment Target - Class 1,2,3 Placement of the BGA solder ball is centred and shows no offset of the ball to land centres. Defect - Class 1,2,3 Solder ball offset violates minimum electrical clearance.

77 IPC 610D draft Inspection Criteria Plastic BGA - Solder Ball Spacing Acceptable - Class 1,2,3 BGA Solder balls do not violate minimum electrical clearance. Defect - Class 1,2,3 BGA solder ball spacing violates minimum electrical clearance. Plastic BGA - Component Height Acceptable - Class 1,2,3 Overall height CH) of the component does not exceed maximum specified. Defect - Class 1,2,3 Overall height of the component exceeds maximum specified.

78 IPC 610D draft Inspection Criteria Plastic BGA - Solder Connections Target - Class 1,2,3 The BGA solder ball terminations are uniform in size and shape. Acceptable - Class 1,2,3 No solder bridging. BGA solder balls contact and wet to the land forming a continuous elliptical round or pillar connection. Process Indicator - Class 2,3 BGA solder ball terminations are not uniform in size, shape, coloration, oration, and colour contrast. Defect - Class 1,2,3 No visual or x-ray evidence of solder bridging. A "waist" in the solder connection indicating that the solder ball and the attaching solder paste did not flow together. Incomplete wetting to the land. BGA solder ball terminations have incomplete reflow of the solder paste. Fractured solder connectionnection

79 IPC 610D draft Inspection Criteria Plastic BGA Voids Acceptable - Class 1,2,3 Less than 10% voiding in the ball to board or ball to component interface. Process Indicator - Class 2, % voiding in the ball to board or ball to component interface. Defect - Class 1,2,3 More than 25% voiding in the ball to board or ball to component interface.

80 Mechanical Inspection

81 Mechanical Inspection

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83

84 Surface Fibre Contamination

85 Solder Balls

86 Excessive Time and Temperature

87 BGA Optical Inspection

88 BGA Optical Inspection

89 Inspection of BGA Board Assemblies Measure Stand-Off Height

90 Inspection of BGA Board Assemblies Measure Stand-Off Height

91 Inspection of BGA Board Assemblies Measure Stand-Off Height Weight will depress balls