In
terms of power chip assembly, the existing main problems are: the assembled
chips, due to the bottom of the hollow area is more, thermal resistance is
bigger, work have a lot of heat when not through the effective way to transfer
to the shell, resulting in junction temperature is exorbitant, while working
reliability, reduce the life of the power device, even 1 thermal breakdown
failure by junction temperature is too high. In recent years, with the rapid
development of the electronics industry, vacuum sintering process has been
widely used, and the voidage rate, thermal resistance, connection strength and
reliability have been significantly improved, which may become one of the key
technologies for power chip assembly.
1. The sintering mechanism
Two different
metals can form eutectic alloys in proportion at temperatures well below their
respective melting points. This lower temperature is their low eutectic point. Sintering
process is in between the chip and carrier (substrate) or pipe shell of a metal
sheet (solder), in a certain vacuum or protective atmosphere heating to the
alloy melting point make it melt, melt into liquid alloy infiltrating the whole
chip welding metal and carrier surface of substrate, solder welding the weld
metal and carrier with the metal physical and chemical reaction, generate a
certain amount of intermetallic compound, and then, in the process of cooled to
below the melting point of solder and intermetallic compound chip and carrier
welded together, form good ohmic contact, thus complete the chip and carrier
welding drawing.
In this paper, the tunnel sintering furnace and vacuum sintering furnace are selected respectively to
weld the chip and DBC board, and the cavity rate of the two technologies is
compared and analyzed through X-ray scanning, which proves that the actual effect
of vacuum sintering process is better.
2. Sintering process test of
tunnel furnace
The use of tunnel furnace
heating, in DBC board and chip add solder piece, when the solder piece by heat
melting, with the help of it on DBC board coated copper part of mutual melting
and the formation of metal compound, achieve new alloy surface will chip and
DBC board solidly welded together. The test results are as follows:
FIG. 1 (a) shows the
control curve of sintering temperature in the tunnel furnace. FIG. 1 (b) is the
reflow furnace in FIG. 1, which is a multi-purpose "cold wall"
process welding furnace. Under the condition of observation 1 < a), X-ray
scan diagram of the back side of the chip completed by the tunnel sintering
furnace and benefit window are provided on the top cover of the chamber.
Through it, real-time recording of each stage of the sintering process can be
achieved. Then, the cavity rate of the chip after sintering can be obtained by
the computer as 8, 7%.Adjust the temperature curve in time.
3. Vacuum sintering furnace
process test
Internally open vacuum pump
to extract air (vacuum degree 1 × 10 × 5 mbar);Then the vacuum sintering furnace used in the charge test is a kind of welding nitrogen dilution residual
air with the function of rapid annealing. When the vacuum reaches its limit and
there is basically no residual gas in the chamber, the filled hydrogen begins
to heat up. At high temperature using hydrogen reduction, DBC board, solder and
chip reduction, remove oxide, improve the penetration rate of solder. After a
period of high temperature, the chip has been welded to the DBC board, but
there are still many bubbles on the welding surface. After the vacuum pump is
started for the third time, residual bubbles on the welding surface can be
extracted as much as possible after a period of time, thus reducing the voids
in the chip welding and the voids rate.
The whole process can be
programmed and controlled by computer. The time, gas flow and temperature of
each program section can be precisely set, and the operation is convenient. In
addition, because of the use of solder sheet, do not have flux welding, so that
the sintered chip can be directly sent to the next process, reducing the
cleaning link, reduce production costs. The test results are as follows:
FIG. 2 (a) shows the
control curve of vacuum sintering temperature. FIG. 2 (b) is the X-ray scan
diagram of the back of the chip completed by vacuum sintering under the
conditions of FIG. 2 (). The computer shows that the cavity rate of the chip
after sintering is only 0 coincidence 2%.
4. Interpretation of result
By analyzing and comparing
the results of the above two different sintering processes, it can be concluded
that:
1) Sintering time: vacuum
sintering time is only 1/4 of the time of tunnel sintering furnace, which
greatly improves the production efficiency.
2) Sintering cavity rate: the
vacuum sintering cavity rate (0· 52%) is only 6% of the tunnel sintering furnace
cavity rate (8 · 7%), which reduces by 16 times and significantly improves the
effective welding area.
From the comparison of the above test results, it can be seen
that vacuum sintering can obtain higher quality sintering results than tunnel
furnace sintering process, and the production efficiency and product
reliability can be connected, so that the sintered chips can be directly sent
to the next process, reducing the cleaning link and reducing the production
cost. The test results are as follows:
To significant improvement; And the whole sintering process
is precisely controlled by computer programming to avoid errors caused by human
operation.
5. Conclusion
With the continuous improvement of semiconductor
manufacturing process, vacuum sintering process and related equipment will be
updated and improved day by day, gaining wider recognition and market
application. However, there are many factors that affect the quality of power
chip sintering, which need to be further recognized and explored.
[---This text and text source network, if there is infringement, please contact delete, thank you!---]
No comments:
Post a Comment