Critical Factors in Thru Hole Defects By Ernie Grice Vice President of Sales Kurtz Ersa North America

Transcription

1 Critical Factors in Thru Hole Defects By Ernie Grice Vice President of Sales Kurtz Ersa North America Production needs us

2 Soldering Zone Production needs us

3 Thru Hole Soldering Challenges Seite 3

4 Selective solder masks High potential for defects! 7 mm! Small but deep Cut-outs are requiring a higher wave. Effect: More turbulent wave with more dross creation. Difficult to control the contact time => higher failure rate can be expected Solution from Ersa: Programmable wave height in the solder program. Seite 4

5 Selectiv Solder Masks lead free wave process! Seite 5

6 Typical Thru Hole Defects: Bridging Component Orientation, Lead Length, Pitch, Design Topside Hole Fill Layer Count, Thermal Demand, Lead to Hole Ratio, Design Solder Balls Flux and solder mask Insufficient Solder Flux, Contamination All of These factors can be resolved and more easily managed with Selective Soldering. Seite 6

7 Content Thermal Demand Fundamentals and the Physics of Solder Joints Thick Copper Technologies PCB Layout - Theory and Practice of Heat Traps Soldering defects Preheating Process Soldering Trials Parameters and Results Conclusion Seite 7

8 What is a Good Quality Joint? Goal: 100% Through hole filling Seite 8

9 Target conditions of the IPC A 610 Target Class 1, 2, 3 There is 100% fill This is easy to inspect, there is no cause for any speculation Seite 9

10 Acceptable conditions of the IPC A 610 Acceptable Class 1, 2, 3 Minimum 75% fill Question: How to inspect 75%?? Seite 10

11 Error Pattern insufficient solder and possible consequences Seite 11

12 core conditions at a solder joint to achieve good quality Heat capacity Seite 12

13 Glasübergangstemperatur T G /734 F /644 F /617 F Seite 13

14 Specification temperature of FR4 laminates versus process window Resistance to Soldering Heat Soldering: SAFE UNSAFE DESTRUCTIVE T 288 T D (320 C 390 C)* T 300 * Depending on the specification Seite 14

15 Starting damage of PCB-laminate due to high solder temperature Delamination Copper dissolution Delamination Resin recession Seite 15

16 Copper leaching If a solder joint requires additional heat, the solder temperature should be increased incrementally and very careful. At high solder temperatures, copper leaches very fast, in the worst case the complete pad leaches into the solder (see above). Increase wetting time before increasing solder temperature Seite 16

17 Influence of the layout on the heat management of a solder joint T Top > T M-Sol Capillary gap size Copper connected to the plated through-hole Seite 17

18 Influences of the PCB-Layout on soldering results Seite 18

19 Selective Soldering by miniaturized solder waves Heat transfer by flowing solder within a limited area Seite 19

20 Energy transfer into a solder joint with 100% connection to a copper layer ERSA FhG ISIT Massive heat flow into Cu-layer Seite 20

21 Energy transfer into a solder joint with heat trap present ERSA FhG ISIT Reduced heat flow into Cu-layer Seite 21

22 Heat Traps and their Mode of Action on Printed Circuit Boards Heat traps reduce the heat carrying cross section to those copper layers attached to the joining location Retaining the heat energy in the joining location is improved The joining location heats up more quickly Desired Effect Seite 22

23 Heat Traps - Layout recommendations Seite 23

24 Insufficient usage of top side heaters When the top side heaters can t transfer sufficient energy to heat up the boards top side, all the energy to heat up the solder joint (PCB + pin) must be transfered from the bottom side of the assembly. To ensure a rapid heat up of the solder joint, thermal support vias transfer a large amount of heat additionally to the PCB top side. Seite 24

25 Heat Traps for Busbars- Layout Recommendations X X Dimension: d 4 X d 2 d 3 X d 1 d 1 d 2 + d 3 + d 4 Please Note: The cross sectional area of the bus bar is reduced by the drillings! Seite 25

26 Layout recommendations Heat traps to reduce the heat flow into a massive copper layer. This layout is recommended for all layers of a PCB. Thermal support vias to improve the transfer of heat up to the PCB top side. Reducing the heat capacity of a busbar. Reducing the diameter lowers the heat flow from the pin into the busbar. Note that for all above layout recommendations, the current density has always to be taken into consideration! Seite 26

27 Layout Capillary Action with Wave- and Selective Soldering Ratio of diameter pin through-hole capillary gap To increase the transfer of heat into the plated through-hole, it is recommended to work on the upper limit of the capillary gap. In power electronics the gap is 0,25 0,30 mm Seite 27

28 Calculating the hole diameter for square pins G A = pin dimension D = A x 2 D G = required for insertion d H = D + (2 x G) A G d H Seite 28

29 Possible Sources of Defects in the Selective Soldering Process Soldering System related Same Error Pattern! Component related Typical Error Pattern in Practice Non-Wetting Insufficient Capillary Rise Bridging Copper Leaching Pad- and/or Fillet Lifting SMDs Desoldered Layout Layout Layout Seite 29

30 Conclusion Selective soldering of thick copper PCBs with mini wave systems is possible. The layout of the PCB plays of crucial role - especially the connection of inner layers to THTs and the ratio of pin to hole diameter. The specification of the PCB laminate has to be adapted to the higher solder temperatures. The delamination temperature T D is especially critical! The more copper layers are in the board, the smaller will be the process window for soldering. Seite 30

31 Conclusion The board layout has a large influence on the capillary rise and the formation of bridges The cause variables in the layout are Pad size / Contact spacing Pin length Plating of PTH joined to copper layers Size of capillary gap Distance between THT and SMD Seite 31

32 The Process: Flux (F) Preheat (PH) Soldering (S) Seite 32

33 FLUXING METHODS: Drop Jet Fluxer Airless system. Precise Deposition. 2mm Dot Size. Programmable Flux Amounts per joint. No Clean, Water Soluble and Rosin Up to 15% solids. Ultrasonic Fluxer Precise Deposition. Good for Spraying Rows. Good for High Solids Rosin Fluxes. Spray Fluxer Good for use of Chip Wave Style nozzle in selective. Seite 33

34 Preheating: Top and Bottom Seite 34

35 Preheating Multilayer Boards Telecommunication (24 Layers) T T +++ If, for multi-layer assemblies, thermal energy is supplied only from one side (lower side), then the heat has to travel, layer by layer, from the bottom up through the board. Since each layer absorbs energy, a temperature gradient exists from bottom to top of the board. Therefore, to achieve a uniform and homogeneous heating of the board, a correspondingly long time has to be accepted. T Seite 35

36 Preheating: Multi-layer Boards with IR from bottom LP Bottom Side Surface Temperature ΔT 30K LP Top Side Temperature Critical! 160 C Long Preheat Time 140s IR Preheater only from bottom side, with maximum power (100%)! Seite 36

37 Preheating: Multi-layer Boards with IR from bottom LP Bottom Side Surface Temperature LP Top Side Temperature ΔT 20K High! 150 C Very Long Preheat Time 190s IR Preheater only from bottom side, with reduced power (66%)! Seite 37

38 Preheating Multilayer Boards - Telecommunication (24 Layers) T +++ T T +++ If multi-layer boards are supplied with thermal energy from both sides, the heat penetrates the board simultaneously from top and from bottom. As a result, the temperature gradient is very small, and the board warms up uniformly and homogeneously at a much faster rate. At the same time, the stress experienced by the lower side is reduced, and the danger that the flux is damaged during the preheat process is minimized. Seite 38

39 Preheating: Multi-layer Board with IR from bottom + convection from top LP Bottom Side Surface Temperature ΔT 10K Not Critical! 140 C Preheating from bottom and from top, with reduced power (65%)! LP Top Side Temperature Short Preheat Time 110s Seite 39

40 Forced Convection Top side pre-heating The use of Multijet Forced Convection Optional Top side pre-heating guarantees a constant PCB temperature during the entire selective soldering process. This guarantees that each solder joint is made under the same thermal conditions. Highly recommended for heavy, multilayer PCBs which require a long process. Seite 40

41 Hole Fill Voiding Cu Dissolution Copper Dissolution and The Need For Preheat Interaction Plot for Voiding Interaction Plot for Cu Dissolution 10 Board Thickness/Surface Finish Board Thickness/Surface Finish =.093" 106AX-HT OSP 2 =.093" ImAg 5 1 =.093" 106AX-HT OSP 2 =.093" ImAg Pot Temperature Pot Temperature = Low Voiding (0% - 5%) 5 = Medium Voiding (5% - 10%) 10 = High Voiding ( >10%) 0 = No Dissolution 5 = Slight Dissolution 10 = Total Dissolution Interaction Plot for Hole Fill = 0% - 25% Hole Fill 5 = 25% - 75% Hole Fill 10 = 75% - 100% Hole Fill Pot Temperature 290 Board Thickness/Surface Finish =.093" 106AX-HT OSP 2 =.093" ImAg The more thermal energy you have in your board, the lower your pot temperature And dwell time can be in order to achieve a Good solder joint. No preheat or not enough Preheat warrants higher pot temps and Higher dwell times in order to topside fill On thermally challenging boards. Seite 41

42 The Soldering Module: Things to Consider. Single Point or Multi-dip Moving Pot or Moving the Board Positional Accuracy of the Gantry Pumping Mechanism for Wave Height Dual Alloy Capable Fidicual Recognition Board Warpage Detection Nozzle Types and Sizes Nozzle Cleaning Keep out Areas Seite 42

43 Multi-dip Single Point XYZ Seite 43

44 Multi-Dip Tooling Pros: Fast Cycle Times Cons: Dedicated Tooling Change Over time Tooling Cost Universal Dwell time for all joints Requires Larger Keep out Area More N2 Consumption with Hood Seite 44

45 Reflowlöten Configuration - Single Solder Nozzle - Constant solder flow over the complete nozzle surface no preferred direction for solder to drain - Continuous heat transfer into the solder joint during the solder process - No orientation of the component to the solder nozzle required - No layout constraints for the orientation of the components - Suitable for a wide variety of solder alloys - Individual Wave Height and Dwell Time per Joint Seite 45

46 Moving the Board or the Pot Seite 46

47 Gripper Systems moves the entire PCB with a gripper system, one PCB at a time. Only Localized top side preheat possible. - moving only the solder pot is 50% faster. - no risk of vibration during cooling. - moving solder pot does not require component fixing. - top side preheating keeps PCB temp. constant during soldering. - a machine with segmented process steps can handle up to 6 PCBs at the same time! Seite 47

48 B A C D A D V A N T A G ES: For soldering the square socket just program a line and move the solder nozzle from A to B B to C C to D D to A and peel off It is not required to either turn the board or the solder nozzle, or to change any angles. A recommended orientation of the components is unnecessary Seite 48

49 Repeatability is Critical Seite 49

50 Reflowlöten Design of Solder Bath - Maintenance-free design with electro-magnetic solder pump - No mechanical movable part in the solder bath - Precise wave height due to continuous circulation of solder - Outstanding repeatability of solder process (no impeller) - No adjustment after servicing the solder bath Seite 50

51 Reflowlöten Monitoring - Solder Bath - Solder wave height is measured - Solder level in bath is monitored / Solder wire feeder option - Solder temperature is exactly controlled - N2 atmosphere assures stabile process conditions play video click button Seite 51

52 Solder Module Reflowlöten Seite 52

53 Reflowlöten Configuration Solder Module Z - variable Different nozzle geometries Variety of Alloys - Both solder bath can be raised, separately and individually, on the axis up to the required working height (z- direction) - Depiction of mode of operation with two identical nozzles but different alloys. - Depiction of mode of operation with two nozzles of different geometries and identical solder. Seite 53

54 Reflowlöten Configuration Solder Module Y- variable - The distance of solder bath 1 to solder bath 2 can be adjusted on the axis system in the y-direction. - Set-up for simultaneous soldering of two assemblies of a multi-up panel. Seite 54

55 Reflowlöten Solder Snap-Off with Wettable Nozzle Surfaces F1= Wetting Force F2= Capillary Force F3= Gravity F4= Adhesive Forces - Solder snap-off, the point in the process when the solder breaks off from the solder joint, is positively assisted by the adhesive force F4, which is generated by the wettable surface of the nozzle. - This adhesive force, in conjunction with gravity F3, enables the solder to properly drain off from the solder joint after having formed it, and to eliminate bridging and shorts. Seite 55

56 Reflowlöten Solder Snap-Off with Wettable Nozzle Surfaces Standard Snap-Off - forms convex solder joints Controlled Snap-Off - forms concave solder joints Seite 56

57 Reflowlöten Automatic Nozzle Activation: Automatic, preventive activation of the nozzle surface to prevent the surface from dewetting. The uniform wetting of the outer surface of the solder nozzles is essential for a stable process and constant soldering results. By a charging screw adipic powder will be applied on the solder nozzle in a specified interval. Seite 57

58 Fiducial and Board Warpage The need for fiducial Recognition and Board Warp Detection is highly Dependent on the Assembly. Seite 58

59 Min. distance of a single solder point from the adjacent SMD pad or from the conveyor* BE Pad Bohrung Pin Scrap edge 3 mm 3 mm 6 mm Seite 59

60 Off-centre positioning possibility of the solder wave Seite 60

61 Minimum Distance of a multi-row connector to the adjacent SMD Pads* Component Pad Through Hole 1 mm Seite 61

62 Keep out area around dual and multi row solder joints (pitch 2.54 mm)* Blue = Required keep out area A = distance between pads B = distance between pads 1 mm 2 mm This recommendation should be used for all double and multi row layouts, starting with a pitch of > 2,54 mm. Seite 62

63 keep out areas around selective solder joints No keep out areas or solder thieves required! X Seite 63

64 Programming Methods Joystick Teach : Pro Easy to use Con- VERY Time consuming and Machine is not producing while teaching, Requires live product Offline Programming: Pro Machine runs production while programs created offline, Easy to Use, Auto routing and cycle time calculations, CAD DXF or JPG, Very Accurate! Con- Need Computer Knowledge Data Entry Pro- Can be done while machine is running Con- Requires hand measurements, VERY Time consuming. Seite 64

65 Scale Image Result: Scaled and rotated image Seite 65

66 3D-View of Blocking Zones Visual Monitoring due to 3D-View Seite 66

67 Optimized Line Optimized Cycel Times Seite 67

68 Multi Panel Profils can be easy duplicated Time optimized programming for multi panels Seite 68

69 Parameter-Set Up Selection can be done in the graphic or in the Set-Data-List Seite 69

70 Thank you for your attention!!! We hope we can work with you for your soldering needs. Seite 70