The invention is a semiconductor device assembly and method of making the same. A mounting plate has positioning means for positioning the plate relative to a header, a first mounting surface of the plate is attached to the header and a semiconductor device is attached to a second mounting surface of the mounting plate. The assembly is made by forming the mounting plate, positioning the mounting plate relative to the header by the positioning means, attaching the first mounting surface to the header and the semiconductor device to the second mounting surface. Another method of making the assembly is by defining and etching a mounting plate and attaching the first mounting surface to the header and the semiconductor device to the second mounting surface. This assembly and process provides an efficient means for mounting semiconductor devices and in particular electro-optic devices such as lasers

Dholakia, Anil R.

Trager, Louis

NASA Technical Reports Server

United States Patent 1191 [11] Patent Number: 4,820,659 
Dholakia et al. [45] Date of Patent: Apr. 11, 1989 
[54] METHOD OF MAKING A 
SEMICONDUCTOR DEVICE ASSEMBLY FOREIGN PATENT DOCUMENTS 
Related US. Application Data 
[62] 
[51] Int. Cl.4 ............................................. HOlL 23/12 
[52] U.S. C1. .................................... 437/209; 437/214; 
437/221; 361/386; 357/80; 174/52.5; 29/739 
[58] Field of Search ....................... 437/209, 214, 221; 
361/386; 174/52 H, 357/80; 29/739 
Division of Ser. No. 886,077, Jul. 16, 1986. 
1561 References Cited 
U.S. PATENT DOCUMENTS 
3,419,763 12/1968 Beaudouin ........................ 114/52 H 
3,528,102 9/1970 Rodet et al. ........................ 437/214 
3,771,031 11/1973 Kay ....................................... 357/76 
4,172,261 10/1979 Tsuzuki et al. ....................... 357/80 
4,193,082 3/1980 Dougherty ............................ 357/80 
4,240,090 12/1980 Hughes et al. ........................ 357/81 
4,240,098 12/1980 Zory et al. ............................ 357/81 
4,322,778 3/1982 Barbour et al. ..................... 361/414 
4,394,679 7/1983 Hawrylo ............................... 357/81 
4,584,688 4/1986 Demeure et al. ..................... 372/36 
[75] Inventors: 
[73] Assignee: 
[21] Appl. No.: 
[22] Filed: 
0052920 6/1982 European Pat. Off. . 
Ani1 R. Dholakia, Cranbury; Louis 0101374 2/1984 European Pat. Off. . 
Trager, Raritan, both of N.J. 0171662 2/1986 European Pat. Off. . 
General Electric Company, 
Schenectady, N.Y. 
108,665 
Oct. 15, 1987 
0102059 6/1982 Japan ................................... 437/214 
59-14654 1/1984 Japan ..................................... 357/81 
1030169 5/1966 United Kingdom . 
1066157 4/1967 United Kingdom . 
2192752 1/1988 United Kingdom ................ 437/214 
Primaly Examiner-Brian E. Hearn 
Assistant Examiner-Beverly A. Pawlikowski 
Attorney, Agent, or Firm-William Squire; James C. 
Davis, Jr.; Paul R. Webb, I1 
P71 ABSTRACT 
The invention is a semiconductor device assembly and 
method of making the same. A mounting plate has posi- 
tioning means for positioning the plate relative to a 
header, a first mounting surface of the plate is attached 
to the header and a semiconductor device is attached to 
a second mounting surface of the mounting plate. The 
assembly is made by forming the mounting plate, posi- 
tioning the mounting plate relative to the header by the 
positioning means, attaching the first mounting surface 
to the header and the semiconductor device to the sec- 
ond mounting surface. Another method of making the 
assembly is by defining and etching a mounting plate 
and attaching the first mounting surface to the header 
and the semiconductor device to the second mounting 
surface. This assembly and process provides an efficient 
means for mounting semiconductor devices and in par- 
ticular electro-optic devices such as lasers. 
12 Claims, 1 Drawing Sheet 
36. r30 
13 
/ 24 IO 
42 
https://ntrs.nasa.gov/search.jsp?R=20080008751 2019-08-30T03:32:28+00:00Z
US. Patent Apr. 11,1989 
36, (30 
4,820,659 
13 
Fig. / 
/ 
IO 
34 
32 
30 
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42 
Fig. 2 
4,820,659 
1 
These problems demonstrate that it would be desir- 
able to have an economical and efficient method for 
mounting semiconductor devices on headers. 
METHOD OF MAKING A SEMICONDUCTOR 
DEVICE ASSEMBLY 
2 
mounting plate. 
BACKGROUND OF THE INVENTION 
In mounting semiconductor devices on headers prob- 
lems may arise in the accuracy of alignment of the semi- 
conductor device relative to the header. In particular, 
high power semiconductor lasers must be mounted such 
that the laser’s far field radiation pattern is not distorted 
and, additionally, such that adequate heat dissipation is 
provided. 
A semiconductor laser typically comprises a body 
having a pair of opposed end faces with at least one 
emitting end face. The body includes a substrate having 
a buffer layer thereon, a first cladding layer overlying 
the buffer layer, an active region overlying the first 
cladding layer, a second cladding layer overlying the 
active region and a capping layer overlying the second 
cladding layer with electrical contacts to the substrate 
and capping layer. Primarily, heat is generated in the 
active region which is typically in the shape of a ridge 
which may be three micrometers (pm) or less in width 
in the lateral direction, the direction in both the plane of 
the layers and the end faces. 
When the laser is mounted to a surface of a header, 
the emitting end face must be coplanar with, or extend 
past, the leading edge of the header to prevent reflec- 
tions of the laser light from the surface of the header 
which would distort the laser’s far field radiation pat- 
tern. Generally, heat sinking requirements necessitate 
that the emitting end face extend no greater than 2 pm 
past the edge of the surface of the header. As a practical 
matter these tolerances are difficult to meet since the 
edge of a standard header, viewed microscopically, is 
rough and thus requires polishing to obtain a smooth 
perpendicular edge for mounting. This polishing re- 
moves the plating finish on the header which necessi- 
tates additional plating operations entailing further time 
and expense. 
After the polishing and plating operations, the laser is 
soldered to the header. Standard semiconductor device 
soldering methods are undesirable since these methods 
place the device in the middle of molten solder and 
thereby displace solder around the edges of the device. 
SUMMARY OF THE INVENTION The invention herein described was made in the per- 5 
formance of work under NASA Contract No. NAS The invention is a semiconductor device assembly 
1-17441 and is subject to the provisions of Section 305 which comprises a header and a mounting Plate having 
of the National Aeronautics and space Act of 1958 (72 means for positioning the mounting plate relative to the 
Stat. 435; 42 U.S.C. 2457). header with a first mounting surface of the plate at- 
T K ~  is a division of application ser. N ~ .  886,077, filed 10 tached to the header and a second mounting surface of 
the plate having a semiconductor device attached July 16, 1986. thereto. 
The invention relates to a semiconductor device as- The assembly is made by forming the mounting plate, sembly having a header, a mounting plate attached to positioning the mounting plate relative to the header 
the header and a semiconductor device attached to the 15 attaching the first mounting surface of the plate to the 
header, and attaching the semiconductor device to the 
second mounting surface of the plate. 
A second method of making the assembly is by defin- 
ing and etching a mounting plate and attaching a first 
20 mounting surface of the plate to a header and attaching 
the semiconductor device to a second mounting surface 
of the plate. 
BRIEF DESCRIPTION OF THE DRAWING 
FIG. 1 is a cross-sectional view of the semiconductor 
FIG. 2 is a perspective view of a mounting plate of 
25 
device assembly of the invention. 
the invention. 
DETAILED DESCRIPTION OF THE 30 
35 
40 
45 
50 
55 
The surrounding solder typically shorts various semi- 60 
conductor layers, since a high power laser is typically 
mounted such that the electrical contact opposite the 
substrate is soldered to the header and the semiconduc- 
tor layers are of minimal thickness. Consequently, the 
surface of the header is typically wetted with a thin 65 
layer of indium solder and then the laser is gradually 
positioned on the surface so that the emitting end face is 
coplanar with the leading edge of the header surface. 
PREFERRED EMBODIMENTS 
In FIG. 1 a semiconductor device assembly 10 incor- 
porating the invention includes a header 12 which com- 
prises a base plate 13 with first and second major sur- 
faces 14 and 16, respectively. A stud 20 is attached to 
the first major surface 14, and a mounting bIock 22 is 
attached to the second major surface 16. A lead 24 
extends through and is electrically isolated from the 
base plate 13 and the stud 20 by an insulating material 
26. A mounting plate 30 has a first major mounting 
surface 32 attached to the mounting block 22 and a 
second major mounting surface 34 to which a semicon- 
ductor device 36 is attached. 
The base plate 13, stud 20 and mounting block 22 are 
typically formed of an electrically conducting material 
such as copper with the stud 20 and mounting block 22 
attached to the baseplate 13 by brazing. The insulating 
material 26, such as plastic encapsulant or glass, is in- 
serted to support the lead 24 and provide electrical 
isolation from the baseplate 13 and the stud 20. Gener- 
ally, the semiconductor device 36 is an electro-optic 
device such as a semiconductor injection laser. 
In FIG. 2 the mounting plate 30 comprises a platform 
40 having a means 42 for positioning the plate 30 rela- 
tive to the mounting block 22 and a means 44 for han- 
dling the plate 30. The positioning means 42 is prefera- 
bly a pair of tabs extending from an edge of the plate 30 
in a direction perpendicular to the first and second 
mounting surfaces 32 and 34, respectively. The han- 
dling means 44 is typically a tab extending from an edge 
of the plate 30 in a direction opposite to the direction of 
the positioning means 42. 
The plate 30 is formed of an electrically conducting 
material such as beryllium-copper, silver or, typically, a 
copper sheet. The platform 40 is typically about 250 pm 
or less in thickness and preferably between about 25 and 
125 pm in thickness. When the platform 40 is of minimal 
thickness the heat will primarily be transferred directly 
4,820,659 
3 4 
through the plate 30 to the mounting block 22, having tive to a leading edge of the mounting block 22. A 
minimal heat dissipation throughout the plate 30. Alter- leading edge being a surface connecting the first and 
natively, if the plate 30 is of sufficient thickness heat will second major mounting surfaces 32 and 34, respec- 
be transferred throughout the plate 30, thus providing a tively. A die attacher then positions the device 36 such 
larger surface area resulting in greater heat flow to the 5 that an end face is positioned substantially coplanar 
mounting block 22 which is the primary heat sink. With with a leading edge of the plate 30, which is to include 
the addition of the plate 30, this greater heat flow is the end face of the device 36 extending over an edge of 
desirable since the heat must then pass througli two the plate 30 by about 2 pm. The first mounting surface 
solder junctions which exist between the device 36 and 32 is attached to the mounting block 22 and simulta- 
the plate 30 and between the plate 30 and the mounting 10 neously the device 36 is attached to the second mount- 
block 22. These solder junctions do not conduct heat as ing surface 34 by heating the plate 30 to about 300" C .  
readily as the mounting plate 30 and the mounting block such as by a strip heater. Alternatively, the plate 30 may 
22, and consequently provide less heat dissipation for be first attached to the mounting block 22 or the device 
the assembly 10. Thus, platforms 40 which are at least 36 may be first attached to the plate. A bond wire is 
about 25 pm thick are desirable to provide dissipation 15 then electrically connected from the lead 24 to the semi- 
throughout the plate, although with platforms 40 conductor device 36. 
greater than 250 pm thick it is difficult to obtain sharp The sharply defined edges of the plate 30 eliminate 
edges on the plate 30 when they are microlithographic- the requirement of well-defined edges on the mounting 
ally defined. block 22, thus eliminating the necessity for additional 
The plate 30 is formed in a sheet of suitable material 20 polishing and plating operations. Further, since a de- 
using standard processing techniques such as photoli- sired plating thickness has been formed on the plate 30 
thography and etching techniques such as ion-beam for the simultaneous soldering operation, previous tech- 
milling and similar processes. Typically, a photoresist is niques which were time consuming and additionally 
applied, exposed, developed and the sheet is subse- which may short layers of the semiconductor device 36 
quently etched with a solution such as ferric chloride. 25 are eliminated. 
These techniques, unlike the prior art, form a sharp We claim: 
edge for mounting the device 36. For example, leading 1. A method of making a semiconductor device as- 
edges of accurately machined headers typically have an 
appoximately 12 pm radius, thus making alignment of forming by photolithography and etching a metallic 
the emitting end face within 2 pm of the leading edge of 30 thermally conductive mounting plate having first 
the header difficult. Additionally, even accurate ma- and second major mounting surfaces for attach- 
chining typically leaves burrs extending about 5 pm ment to a header; 
from the surface of the header. Consequently, approxi- attaching said mounting plate to the first surface of 
mately 5 pm thick solder must therefore be interposed said header; and 
between the device and the header, although a maxi- 35 attaching said semiconductor device to said second 
mum of 1 to 2 pm of solder is desirable for heat dissipa- mounting surface. 
tion. Further, machining processes typically use alumi- 2. The method of claim 1, wherein the step of forming 
num-oxide or silicon-carbide polishing grits which the mounting plate further comprises the step of form- 
leave particles embedded in the surface which inhibit ing a positioning means in said plate comprising at least 
uniform plating or soldering. In contrast, the present 40 one tab extending from said plate. 
process produces plates having a leading edge with an 3. The method of claim 1, wherein the step of forming 
approximately 2 pm radius, thus making alignment of said mounting plate further comprises the step of form- 
the emitting end face with the leading edge of the plate ing integral with the plate means for manually position- 
practical. The plate is also free of detectible burrs and ing the plate relative to said header. 
particles embedded in the surface. Additionally, the 45 4. The method of claim 1, further comprises the step 
plates formed by this process may be produced in quan- of positioning an end face of said device such that the 
tity at the same time with relatively consistent charac- end face is substantially coplanar with an edge of said 
teristics, while with a machining process the plates are mounting plate prior to attaching said device. 
formed sequentially with varying quality. 5. The method of claim 1, wherein the step of forming 
Generally the plate 30 is formed such that the length 50 the mounting plate further comprises the step of coating 
and width of the second mounting surface 34 is between 
about 1.5 to 3.0 times the size of the respective length 6. A method of making a semiconductor device as- 
and width of the semiconductor device 36. For exam- 
ple, a laser is typically about 200 pm in width and 300 defining and etching a sheet to form a mounting plate 
pm in length, thus the plate 30 is typically between 5 5  having first and second major mounting surfaces; 
about 300 and 600 pm in width, and 450 and 900 pm in attaching said first mounting surface to a header; and 
length. Although different sizes and geometries of attaching said semiconductor device to said second 
plates may be formed for various heat sinking require- 
ments and different shapes of headers, typically a single 7. The method of claim 6, wherein the step of defin- 
plate 30 geometry may be used for a variety of semicon- 60 ing and etching the mounting plate comprises the steps 
ductor devices and headers. The plates are then bent to 
form the positioning means 42 and the handling means 
44. The plates are then plated with about 2.0 pm of 
nickel and between about 1.0 to 2.0 pm of tin and then 
subsequently separated from one another. 
The plate 30 is positioned on the mounting block 22 
by mechanically grasping the handling means 44. The 
positioning means 42 aids in orienting the plate 30 rela- 
sembly which comprises the steps of: 
the mounting plate with nickel and tin. 
sembly which comprises the steps of: 
mounting surface. 
of: 
forming a photoresist pattern on a sheet; and 
etching said sheet. 
8. The method of claim 6, wherein the step of defin- 
65 ing and etching said sheet further comprises the step of 
forming at least one tab extending from an edge of said 
plate in a direction about perpendicular to said first 
mounting surface. 
5 
4,820,659 
6 
ing plate is about 250 pn or less in thickness. 
electrically conducting material. mounting plate. 
step of attaching a light emitting device to said mount- 
The method of claim 6, wherein said sheet is an 5 ing plate such that an emitting end face of the device is 
substantially coplanar with a leading edge of said 
* * * * *  11. The method of claim 6, wherein the step of form- 
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Method of making a semiconductor device assembly

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