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Flip Chip Assembly in Air. Antonio Prats March 2002. Very low oxygen levels in reflow allow good yields over a wide range of conditions Unfortunately, nitrogen can be expensive in certain regions Reflow in nitrogen can increase the chance of tombstoning with small 0201 and 0402 components - PowerPoint PPT Presentation
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March 6, 2002
1
Flip Chip Assembly in Air
Antonio Prats
March 2002
March 6, 2002
2
Flip Chip Assembly in Air
Very low oxygen levels in reflow allow good yields over a wide range of conditions
Unfortunately, nitrogen can be expensive in certain regions
Reflow in nitrogen can increase the chance of tombstoning with small 0201 and 0402 components
It would be nice to have an air reflow process for flip chip assembly
March 6, 2002
3Universal Consortium Flip Chip Test
Substrate
Trench and Pads
Trench and
Pads
March 6, 2002
4
Air Reflow ProfilesProfile A was Also Run with 1000 ppm Oxygen
169
228
210
152
0
50
100
150
200
250
0 50 100 150 200 250 300 350
Seconds
Tem
per
atu
re (
°C)
FCiA Profile A
FCiA Profile B
March 6, 2002
5Paste Fluxes and Liquid Fluxes
TSF-6522Kester
TSF-6502Kester
R903Kester
KS17-99B-2Kester9603Kester
KS17-99B-1KesterTAC23Indium
FC-NC-LT-BIndiumFC-NC-LT-DIndium
FC-NC-HT-BIndiumFC-NC-LT-CIndium
CL84 - 7897HeraeusFC-NC-HT-CIndium
9171Alpha MetalsTF-38Heraeus
RC-15AlmitCF2400Alpha Metals
BM1-RMA-5000AlmitBM1-RMAAlmit
ProductManufacturerProductManufacturer
Liquid FluxesPaste Fluxes
March 6, 2002
6Very Poor Soldering
Alpha Metals CF2400, Hot Air
Heraeus TF38, Cool Air
3.7 mil
March 6, 2002
7
Poor Soldering
Indium FC-NC-LT-C, Hot 1010 ppm Oxygen
Exposed Gold
March 6, 2002
8No Electrical Failures but Poor Soldering
Almit BM1-RMA-NC, Cool Air
March 6, 2002
9
No Electrical Failures but Poor Soldering
Indium TAC023, Hot Air
Exposed Gold
March 6, 2002
10Good Soldering
Indium TAC023, Cool Air
Kester R903, Cool Air
Almit BM1-RMA-NC, Hot 985 ppm Oxygen
2.6 mil
March 6, 2002
11Fluxes that Exhibited Good Soldering
Hot Profile with 1000 ppm Oxygen Almit BM1-RMA-NC
Alpha Metals CF2400
Indium TAC023
Kester 9603
Kester R903
Indium TAC023
Kester R903
Cool Profile in Air
<none>
Hot Profile in Air
Hot Profile: Peak 228°C, end of soak 168°CCool Profile: Peak 210°C, end of soak 152°C
March 6, 2002
12
Jet Dispensing of Liquid Fluxes for Flip Chip Assembly
Antonio Prats
March 2002
March 6, 2002
13
Jet Dispensing of Liquid Fluxes for Flip Chip Assembly
In the past, spray fluxing of water-soluble or no-clean liquid fluxes did not offer a robust assembly process
It is time to re-evaluate liquid fluxes and look at the Asymtek Dispense Jet process
March 6, 2002
14
Jet Dispensing of Liquid Fluxes for Flip Chip Assembly
Piston is Seated Piston Retracts,Flux Fills
Piston Returns,Forces Material Out,
Followed by Air
March 6, 2002
15Dispense Pattern for Jetted Flux
March 6, 2002
16
Jet Dispensing of Liquid Fluxes for Flip Chip Assembly
Some Fluxes Volatilize Quickly• Only one leaves behind a tacky film (Alpha Metals 9171)• The rest leave a non-tacky film that does not hold a flip
chip in place
Other Fluxes Do Not• These fluxes remain fluid through die placement
March 6, 2002
17List of Liquid Fluxes That Were Evaluated
“Volatile” fluxes are those which dried before the die could be placed. The other fluxes remained liquid for die placement.
ZR-102FSenju
KS19-77AKester
KS17-133BKester
9171 (tacky)Alpha Metals
RC-15Almit
ProductManufacturer
Volatile Liquid Fluxes
KS17-99B-2Kester
KS17-99B-1Kester
FC-NC-LT-BIndium
FC-NC-HT-BIndium
CL84 - 7897Heraeus
BM1-RMA-5000Almit
ProductManufacturer
Less Volatile Fluxes
March 6, 2002
18
Air Reflow ProfilesFluxes Showed No Preference
169
228
210
152
0
50
100
150
200
250
0 50 100 150 200 250 300 350
Seconds
Tem
per
atu
re (
°C)
FCiA Profile A
FCiA Profile B
March 6, 2002
19Residue and Some Bridging with Liquid Fluxes
Indium FC-NC-LT-B, 1010 ppm Oxygen
Almit BM1-RMA-5000, cool air
March 6, 2002
20
Alpha Metals 9171Flux Residue Varies from “Excessive” to “Very Little”
March 6, 2002
21
A good liquid flux will:• Promote good soldering without solder bridges• Hold the die in place through reflow
– By remaining liquid or– By volatilizing and leaving behind a sufficiently tacky film
• Not leave excessive amounts of residue
We should be able to dispense less flux, and see what effect that has upon the amount of residue
At this time, we have no information on underfill compatibility with these fluxes. This will be very important.
Summary
