Page 64
www.us-
tech.com
May, 2019
Reducing CTE Mismatch Defects in Flip Chip Reflow
By Patrick Gao, Shoubing Ni, Thomas Tong, and Joe Yang, BTU International, Inc. T
he miniaturization of electronic components has led to the use of copper pillars, smaller bump sizes and narrower pitches. This has
resulted in lower flexibility of joints and more sen- sitivity to the influence of coefficient of thermal expansion (CTE) mismatch. Component tilt, open solder joints and cracks with the use of extreme low-K (ELK) dielectric materials are defects that increase with this trend. BTU’s solution, TrueFlat technology, which
uses negative pressure reflow is designed to allevi- ate yield losses due to CTE mismatch during reflow soldering. Advanced thermal control (ATC) is introduced to control the rates of heat transfer for processes sensitive to abrupt expansion and contraction. ATC is an enhancement of existing control for
heating and cooling rates to achieve continuous, uniform heat transfer. This provides the ability to control the abrupt expansion and contraction stress produced by micro spikes.
Challenges of Miniaturization Silicon flip chip and thin organic substrates
have significantly different CTEs. CTE mismatch for flip chip on thin substrates has been a chal- lenge for more than 10 years. Controlling defects in mass reflow caused by warpage- and CTE stress-related cracks has long been the focus of reflow process engineers. Other reflow techniques, such as thermal compression bonding, are avail- able. However, these processes are expensive and have low throughput, which makes mass reflow a preferred process. Existing mass reflow methods to alleviate the
effects of CTE mismatch consist of a solid carrier acting as a heat spreader, a cover plate to attempt to hold down the substrate during reflow and the
CableEye
Whether you're an R&D engineer designing cables for a new product or a production worker checking hundreds of cables an hour, CableEye's unique graphic wiring display tells you what you need to know clearly and immediately. Graphically see missing or shorted conductors, miswired cables, reversed diodes, twisted-pair errors, and backward connectors. Print crystal-clear test results including the wiring schematic. Graphically compare two cables by alternating the display between your test result and the ideal cable. Run a high-speed resistance test loop while you flex the cable
use of a slow cooling process to control the rate of contraction. This method is being challenged as miniaturization continues. The use of a reduced or negative pressure
(pressure below atmosphere) below the carrier throughout the entire reflow process enhances the contact of the substrate on the carrier and helps to keep the substrate flat.
match. Ensuring contact with the carrier helps to keep the substrate flat and reduces deformation.
Negative Pressure Reflow To demonstrate experimentally, this requires
two stages. The first stage is to ensure effective contact of the substrate to carrier. The second is to control the heating rates for the reflow process. The objective of negative pressure reflow is to gen- erate a continuous suction from the start of heat- ing to the end of the cooling process within the heated chamber. A slow cooling rate profile is adopted to minimize the impact of heat spikes. Figure 1 demonstrates the gas flow to gener-
ate effective suction with edge rail conveyors. Redirection of gas flow on the bottom of the process produces a suction box effect, and a pressure below atmosphere, directly below the conveyor and prod- uct — hence the name “negative pressure reflow.” The carrier design is important for uniform
Figure 1: Negative pressure reflow design. This enhances localized contact below the
chip, where a cover plate is not effective. More effective heat spreading produces greater temper- ature homogeneity and reduces the impact of abrupt expansion and contraction due to CTE mis-
®
Highly Versatile Test and Cable Management System for Cables and Wire Harnesses Fault
CableEye Wiring Report Name: HD44M-HD44F-S39X
Socket L HD44 Male
SH 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 21 22 23 24 25 26 27 28 29 30 16 17 31 32 33 34 35 36 37 38 39 40 41 42 43 44 M A T C H D A T A 1-6-18 10:57 AM
Print your company information here. Set up in Preferences / Print Options. Z-AXIS CONTROLLER CABLE
Socket R HD44 Female
SH 31 32 33 34 35 36 37 38 39 40 41 42 43 44 21 22 23 24 25 26 27 28 29 30 5 6 7 8 9 10 11 12 13 14 15 16 2 3
suction and heating. A large suction hole size cre- ates localized heat spikes. The recommended layout is 0.04 in. (1 mm) diameter hole grid below the sub- strate. There are window and mesh top covers used in standard reflow ovens without suction. Mesh has the advantage of holding down the edges of each chip but has less flexibility and costs much more to produce. Window covers hold down the edges of the substrate and allow different layouts of chips on the substrate. The center of the substrate is subjected to deformation, as there is nothing ensuring proper contact of the substrate to the carrier. Pressure should be measured below the carri-
er with a room temperature fixture overlaid onto a ramp to spike (RTS) slow-cool temperature profile — measured in the same oven. If the suction remains effective throughout the process, it
Continued on next page
N E T L I S T
L-SH L-1 L-2
-L-3 L-4 L-6 L-7 L-8 L-9
Visualize Wiring Schematically or by Netlist with Color-Coded Errors. See Full Measurement Data for Every Connection.
Model M3U, Expandable to over 2500 Test Points. Use with Laptops Too!
to check for intermittent connections. Trace hidden wires graphically with our minihook probes. Rapidly identify the wiring of unknown cables. Easily automate your tests, log test results and print batch reports.
camiresearch.com/testimonials
Continuity Resistance 4 Wire
See at EWPTE, Booth 2309 Touch-Screen Compatible.
L-10 L-11 L-12 L-13
R-SH L-17 R-2
+R-3
L-5 R-5 R-6 R-7 R-8 R-9
R-10 R-11 R-12 R-13
N O T E S
Z-AXIS CONTROLLER CABLE Connector Type: High-density Dsub, 44 pins. Connector must have machined pins and metal shell. Use AMP part 778224-6.
NOTE: Pins 10-15 and 40-44 of this high-density cable carry rarely-used signals and may not be wired in the cable you are testing. This is acceptable.
L A B E L
Z-AXIS CONTROLLER Part Number 355-425A
CableEye® by CAMI Research Inc.
Fully Document Cables for your Own Records or for your Customers'.
How much is your time worth? Chances are that it won't take long for CableEye to earn back your investment. Basic systems start at $1295. Operating software included. READY TO USE!
TAKE A
FREE 2 WK TEST DRIVE!
CAMI Research Inc. ®
CableEye +1 978-266-2655 |
sales@camiresearch.com ®
s 0.5
e c
.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124
