31
Indium Corporation
© Indium Corporation
Medical PCB Assembly & Solder Paste
Solder paste Requirements
• SAC305 or SnPb alloys• Flux compatibility with
cleaning process• High Electrical Reliability• Low Voiding• Good printing
Cleaning Challenges after Paste Reflow
• High impedance front-end• Flux residues can “short out”
front-end, particularly under humid conditions
High Electrical ReliabilityStringent SIR Requirements
Spacing = 0.2mmSpacing = 0.5mm
Electrical Reliability for Low-Standoff Component
Dendritic growth
RCOOH encapsulated in solid rosin, incapable of engaging in corrosion reaction
Activator RCOOH in flux
RCOO- + H+
mobile in liquid environment
Solvent dried out
H2O H+ engage in corrosion reaction
Solvent retained
Flux Activator & Solvents during Reflow of Low-Standoff Components
7
Flux Chemistry DesignSIR Electrical Reliability Test
1
2
3
4
5
I
X1 2
34
5 I
X
X X
X
SIR - Standard SIR + Glass Slide
© Indium Corporation
Voiding
- 225u Square
Apertures (9)
- 7.75mm square
ground plane
P5 Profile
Hot Profile
Check effect of
temperature & time
on voiding
© Indium Corporation
Voiding
Hot Profile P5 Profile Hot Profile P5 Profile
Paste A Paste I
Paste A (mean void%) Paste I (mean void%)
Hot Profile 22.73% 7.34%
P5 Profile 37.34% 11.58%
Printing – Transfer Efficiency
Slide #11
2-hours 4-hours1-hour
Printing – Response to Pause
Slide #12
Volu
me(%
)
0
25
50
75
100
125
150
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
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317
222
223
224
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235
236
237
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240
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242
243
244
245
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
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148
149
102
103
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105
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54
55
56 57
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61 62
63
64
65
66 67
68
69
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71 72
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75
76 77
PCB ID
0 Hours 1 Hour 2 Hours 4 Hours 0 Hours 1 Hour 2 Hours 4 Hours 0 Hours 1 Hour 2 Hours 4 Hours 0 Hours 1 Hour 2 Hours 4 Hours 0 Hours 1 Hour 2 Hours 4 Hours 0 Hours 1 Hour 2 Hours 4 Hours RTP
25 mm/s 50 mm/s 100 mm/s 25 mm/s 50 mm/s 100 mm/s Print_Speed
Q230 Indium8.9E (593-6-1) Paste_ID
Std
Dev
0
10
20
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
54
55
56 57
58
59
60
61 62
63
64
65
66 67
68
69
70
71 72
73
74
75
76 77
PCB ID
0 Hours 1 Hour 2 Hours 4 Hours 0 Hours 1 Hour 2 Hours 4 Hours 0 Hours 1 Hour 2 Hours 4 Hours 0 Hours 1 Hour 2 Hours 4 Hours 0 Hours 1 Hour 2 Hours 4 Hours 0 Hours 1 Hour 2 Hours 4 Hours RTP
25 mm/s 50 mm/s 100 mm/s 25 mm/s 50 mm/s 100 mm/s Print_Speed
Q230 Indium8.9E (593-6-1) Paste_ID
Paste A Paste I
Minimum DeviationMore Deviation
Area Ratio = 0.58 Apertures = 0.25mm dia
Au Solders in Medical Assembly
Au Solders in Medical Assembly
High-Strength 80Au/20Sn Solder in Medical Assembly
15 INDIUM CORPORATION CONFIDENTIAL
• Catheters
• Endoscope
• “In Vivo” MEMS &
Sensors
Solder Nitinol &
Stainless Steel
• 80Au/20Sn (Wire,
Washer preform)
• Flux
High-Strength 80Au/20Sn Solder in Medical Assembly
Very fine wire:
25-250u diameterVery thin preform:
13u thickness
© Indium Corporation
Au Solders in Implantable Devices
• Pure Gold is inert and often used for biocompatibility reasons
• Precision, high aspect ratio (thin wall/thick), Au washers are required for feed-through apps
• Complex/compound Au “racetrack” designs for sealing batteries and connection boxes
• High purity standards and stringent quality specifications
Complex Au Solder Preforms in Medical Assembly
18 INDIUM CORPORATION CONFIDENTIAL
• Standard aspect ratio = 1.5
(ratio of max thickness to wall)
• Ability to increase the
aspect ratio for wider
process window
© Indium Corporation
Au & In Solders for Hermetic Sealing
• Hermetic seal often required to protect delicate components from harsh conditions
• Sealing optics in medical devices typically a flux-less process
• AuSn in a flux-less process is ideal for hermetic sealing primarily due to oxide resistance and high reliability characteristics
• Indium and Indium alloys are ideal for cryogenic sealing due to their malleable and ductile properties even at extremely low temperatures
© Indium Corporation
Integrated Solder Preforms Monitoring & Diagnostic Devices
Flux-Coated Preforms for Cavity Soldering
Current Process
• Paste printed inside
cavity + Preform
(depth 0.15 + 0.1/-0 mm)
• >> 20% voids - rejects
• Reject Rate with solder
paste = 25%
Flux-Coated Preforms for Cavity Soldering
9.27mm x 5.59 mm; 300µ thick
Low Voiding << 5%
Very Good Wetting
In Solders as TIMs (Thermal Interface
Materials)
Thermal Conductivity
• 100In; k= 87 W/m.K
• Grease/PCM; k= 3-10 W/m.K
Pumpout
• No pumpout with Solder-TIM
• Grease/PCM migrates from the
center; poor thermals
Bakeout
• No bakeout with Solder-TIM
• Grease/PCM becomes powdery
with bakeout ; poor thermals
Thermal Management : Solder-TIMs vs Thermal Grease / Phase Change Materials
Clamping Force
Low
Spot
High
Spot
Base surfaceTIM
Heat-Spring® Compressible Solder-TIM
Heat-Spring®• Compressible Solder-TIM
• Surface altered for lower interface resistance
• Only needs compression force (3-4 bar)
• No heat, No melting, No Metallization, No flux, No Voiding
26
Effect of Compression on Interface ResistanceGrease vs Flat Solder Foil vs In Heat-Spring®
27
Time 0 Time 0
88 - 90 86 - 88 84 - 86 82 - 84 80 - 82 78 - 80 76 - 78 74 - 76 72 - 74 70 - 72 68 - 70 66 - 68 64 - 66 62 - 64 60 - 62
1561 Hr. @90C1597 Hr. @90C
88 - 90 86 - 88 84 - 86 82 - 84 80 - 82 78 - 80 76 - 78 74 - 76 72 - 74 70 - 72 68 - 70 66 - 68 64 - 66 62 - 64 60 - 62
3108 Hr. @90C 3056 Hr. @90C
88 - 90 86 - 88 84 - 86 82 - 84 80 - 82 78 - 80 76 - 78 74 - 76 72 - 74 70 - 72 68 - 70 66 - 68 64 - 66 62 - 64 60 - 62
Heat-Spring® Grease Heat-Spring® Grease
Heat-Spring® Grease
Grease vs Heat-Spring®Bake Test @ 90 deg C; T = 0, 1500, 3000 hrs
Grease pumps out of
the interface, leaving
the center dry
Heat-Spring®
conforms to the
interface, leaving the
interface cooler
28
Grease / PCM
Heat-Spring®
0-50W, 3min ON / 2min OFF, 1000 cycles
Heat-Spring® Resists PumpoutPower Cycling: 0-50W, 3min ON / 2min OFF, 1000 cycles
Grease vs Heat-Spring®Power Cycling: 0-50W, 3min ON / 2min OFF, 1000 cycles
Grease pumps out of
the interface, leaving
the center dry
Heat-Spring®
conforms to the
interface, leaving the
interface cooler
NanoFoil®
Thank You…
