Current protector

A current protector comprising an organic resin-made insulating substrate, a pair of terminals formed at both ends of the insulating substrate, and an electrical conductor electrically connecting the terminals and having a thickness of 3-8 .mu.m and formed in or on the insulating substrate, is excellent in suppressing ignition and smoking at the time of blowing, and can be improved in clearing characteristics by various modifications.

BACKGROUND OF THE INVENTION 
This invention relates to a current protector, particularly an organic 
resin-made chip type current protector and processes for producing the 
same. 
Current protectors are used for protecting electronic devices from 
over-current acting as an automatic circuit-interrupting device. The 
current protector used in the present invention is connected in series to 
an electric circuit and is subjected to blowing of a fusible link in the 
current protector under over-current conditions so as to protect devices 
by breaking an electric current thereafter. Such an element is generally 
called a fuse. When the term "fuse" is used, the element should satisfy 
the required properties specified in various regulations. But with recent 
diversification of electronic devices, there appear current protectors 
having properties different from those specified in the regulations for 
the fuse. In the present invention, the term "current protector" is used 
in a wide meaning including conventional fuses and having the properties 
and operational mechanism mentioned above. 
As over-current protecting devices, there can be used as electronic 
switches using thyristors or transistors in addition to the 
above-mentioned current protectors. But such devices were not always 
suitable for devices which require miniaturization and a low consuming 
electric power such as portable devices operated by a battery due to an 
increase in circuit parts and an increase in electric power consumed by a 
protective circuit. 
As current protectors having improved properties, JP-A-60-143544 disclosed 
a current protector (or fuse) comprising a ceramic substrate and formed 
thereon a three-layered electrical conductor comprising a first layer of 
silver or silver-palladium, a second layer of nickel and a third layer of 
solder or tin so as to improve clearing (or blowing) characteristics at 
the time of soldering. It was also disclosed therein to cover the 
electrical conductor surface with an incombustible (or fire retardant) 
resin such as a silicon resin. But such a structure wherein the fuse was 
formed on the ceramic substrate which is small in thermal resistance, was 
high in heat dissipation and had a problem in that a current value for 
blowing often changed depending on ambient temperatures, even if covered 
with the incombustible (or fire retardant) resin as disclosed by 
JP-A-60-143544. 
In order to solve the problem of using the ceramic substrate, it was 
proposed to use organic resin-made insulating substrates. But when an 
epoxy resin, a phenol resin, a polyimide resin, etc. were used as the 
substrate, there were problems in fuming and combustion. 
JP-A-5-166454 disclosed the use of a fluorine resin as the insulating 
substrate so as to lower thermal conductivity compared with ceramic and to 
improve blowing accuracy of the fuse. The surface of fuse was also covered 
with a silicone resin (rubber). 
On the other hand, the fusible link of the fuse was formed by printing or 
plating (JP-A-63-141233). But the accuracy for forming the fusible link 
was low and particularly it was difficult to control the thickness of the 
fusible link. Thus, it was difficult to make scattering of resistance 
value of the fusible link between lots within 30%. 
According to JP-A-5-166454, the fusible link was formed by forming a thin 
metal layer by plating, followed by etching. Such a fusible link was 
excellent in clearing (or blowing) characteristics, but poor in 
controlling the uniform thickness of plated layer due to difficulty in 
controlling of plating conditions such as the composition of a plating 
bath, etc. Thus, it was difficult to make the scattering of resistance 
value between lots within 30%. Further, since the fusible link was formed 
by etching of plated thin metal layer according to JP-A-5-166454, it was 
impossible to obtain sufficient connection reliability for a long period 
of time when subjected to an accelerated test of heat cycle test. In 
addition, according to JP-A-5-166454, since the surface of fusible link 
was covered with the silicone rubber, the silicone rubber was often 
damaged and caused slight fuming for 1 or 2 seconds due to high 
temperatures at the time of blowing depending on over-current conditions. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide current protectors 
excellent in suppressing fuming and ignition at the time of blowing while 
suppressing heat dissipation, and processes for producing the same. 
The present invention provides a current protector comprising an organic 
resin-made insulating substrate, a pair of conductive terminals formed on 
both ends of the insulating substrate, and an electrical conductor for 
electrically connecting the terminals, said electrical conductor including 
one or more fusible links, formed in or on the insulating substrate and 
made of a metal layer having a thickness of 3 to 8 .mu.m. 
The present invention also provides a current protector having the 
structure as mentioned above and characterized in that the electrical 
conductor is formed on the insulating substrate and has three or more odd 
number of high resistance portions formed by narrowing the width of 
electrical conductor, and low resistance portions connecting the high 
resistance portions, respectively, one of the high resistance portions 
being positioned in the center of the electrical conductor and the rest of 
the high resistance portions being positioned symmetrically with regard to 
the central high resistance portion. 
The present invention further provides a current protector having the 
structure as mentioned above in the form of a chip and characterized in 
that the electrical conductor is formed on the insulating substrate and 
covered with a fluorine resin layer having a thickness of 40 to 200 .mu.m, 
and processes for producing the same. 
The present invention still further provides a current protector having the 
structure as mentioned above in the form of a chip and characterized in 
that the electrical conductor is formed in the insulating substrate and 
sandwiched by a pair of light-shielding metal foils, and processes for 
producing the same. 
The present invention also provides a current protector having the 
structure as mentioned above in the form of a chip and characterized in 
that the insulating substrate is made from a fluorine resin, and when the 
electrical conductor is formed on the insulating substrate, it is covered 
with a fluorine resin, and processes for producing the same. 
The present invention further provides a current protector having the 
structure as mentioned above in the form of a chip and characterized in 
that a vacant space is formed between the electrical conductor and the 
resin layer placed thereon. 
The present invention still further provides a current protector having the 
structure as mentioned above in the form of a chip and characterized in 
that the electrical conductor is formed in the insulating substrate and a 
vacant space is formed at least a portion around the electrical conductor 
to be blowed, and processes for producing the same. 
The present invention also provides a current protector having the 
structure as mentioned above in the form of a chip and characterized in 
that the electrical conductor has a space or a non-adhesion portion with 
regard to the underlying insulating substrate, and processes for producing 
the same.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The current protector of the present invention comprises an organic 
resin-made insulating substrate, a pair of conductive terminals formed on 
both ends of the insulating substrate, and an electrical conductor for 
electrically connecting the terminals, said electrical conductor including 
one or more fusible links, formed in or on the insulating substrate and 
made of a metal layer having a thickness of 3 to 8 .mu.m, provided that 
when the electrical conductor is formed in the insulating substrate, the 
electrical conductor is covered with a resin layer. 
As the organic resin-made insulating substrate, there can be used a 
material comprising an organic resin and a reinforcing material. As the 
organic resin, there can be used a fluorine resin, a phenol resin, an 
epoxy resin, a polyimide resin, etc. As the reinforcing material, there 
can be used glass cloth, glass paper, polyamide cloth, polyamide paper, 
etc. The reinforcing material is not always included in the insulating 
substrate uniformly. Sometimes, the reinforcing material can be included 
in the insulating substrate in half, or in various forms and various 
proportions. 
The use of fluorine resin in the insulating substrate is particularly 
preferable, since the fluorine resin per se is difficult to burn and 
hardly generates smoke. Examples of the fluorine resin are 
polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene 
copolymers, tetrafluoroethylene-ethylene copolymers, 
tetrafluoroethylene-perfluoroalkoxyethylene copolymers, fluorine resins 
modified with other organic resins, naphtha, white oil (liquid paraffin), 
etc. From the viewpoint of cost, the use of polytetrafluoroethylene is 
preferable. Considering low molding temperatures, the use of 
tetrafluoroethylene-perfluoroalkoxyethylene copolymers, 
tetrafluoroethylene-ethylene copolymers is preferable. 
The electrical conductor includes one or more fusible links and 
electrically connects a pair of terminals. The thickness of the electrical 
conductor is 3 to 8 .mu.m. When the thickness is less than 3 .mu.m, it is 
difficult to maintain the thickness accuracy and the generation of pin 
holes is inevitable. On the other hand, when the thickness is more than 8 
.mu.m, it is difficult to form the electrical conductor which blows 
precisely under over-current conditions. The width of the electrical 
conductor is preferably 70 .mu.m or less. 
The electrical conductor can be formed by using a metal foil such as an 
ultra-thin copper foil, an ultra-thin copper foil carried on aluminum, a 
second copper layer (ultra-thin copper layer) of a composite metal foil 
(e.g. a composite metal foil comprising copper (carrier)/nickel alloy 
(stopper)/copper (ultra-thin copper) disclosed in U.S. Pat. No. 
5,403,672). 
Considering the object of the present invention, the accuracy of thickness 
of the metal foil is very important. In order to suppress the scattering 
of resistance value of the electrical conductor within 15%, it is 
necessary to maintain the accuracy of thickness of metal foil within about 
.+-.5%. In order to suppress the scattering of the resistance value within 
12%, it is necessary to make the thickness accuracy of metal foil about 
.+-.3%. 
The ultra-thin copper foil and composite metal foils can be produced by an 
electrolytic process, a rolling process, and the like. The accuracy of the 
thickness is acceptable even for those available commercially. According 
to the results of weight measuring (in the case of a composite metal foil, 
the ultra-thin copper layer being dissolved and measured), the scattering 
is about .+-.1% in the same lot with regard to the average value. Although 
the required thickness accuracy changes depending on the allowability of 
scattering of resistance value, the thickness accuracy of metal foil is 
preferably within .+-.5%, more preferably within .+-.3%, from the above 
results. 
The electrical conductor can be formed on the surface of the insulating 
substrate or can be included in the insulating substrate. In the case of 
forming the electrical conductor on the surface of insulating substrate, 
the resin layer covering the electrical conductor can be formed by coating 
of a resin or pressing of a resin film. In the case of including the 
electrical conductor in the insulating substrate, the resin layer of the 
insulating substrate (the resin layer portion of insulating substrate 
positioned between the surface and the electrical conductor) corresponds 
to the resin layer mentioned in the above case. 
The electroconductive terminals positioned on the same level as the 
electrical conductor are better when thick from the viewpoint of 
prevention of blowing by thermal stress. But from the viewpoint of 
material cost and moldability, it is better that the terminals are not too 
thick. Preferable thickness is about 10 to 50 .mu.m. When the thickness of 
terminal is less than 10 .mu.m, there is a tendency to lower mechanical 
strength, and to easily break the bonding at the boundary of the terminal 
portion and the terminal connecting portion under repeated influence of 
temperature changes. On the other hand, when the thickness is over 50 
.mu.m, properties are not changed while the production cost increases. 
The electroconductive terminals can be formed by plating and etching, e.g. 
(i) conducting plating on necessary portions of an ultra-thin copper foil, 
followed by etching of the rest of the ultra-thin copper foil to form an 
electrical conductor, (ii) retaining a part of a carrier copper of a 
composite metal foil copper (carrier)/nickel alloy (stopper)/copper 
(ultra-thin copper)! by etching, peeling the exposed stopper layer, and 
forming an electrical conductor on the ultra-thin copper portion, and the 
like method. 
The current protector of the present invention can be modified variously to 
provide various additional effects as mentioned below. 
First modification! 
The current protector having the structure as mentioned above can be 
modified in that the electrical conductor is formed on the insulating 
substrate and has three or more odd number of high resistance portions 
formed by narrowing the width of electrical conductor, and low resistance 
portions connecting the high resistance portions, respectively, one of the 
high resistance portions being positioned in the center of the electrical 
conductor and the rest of the high resistance portions being positioned 
symmetrically with regard to the central high resistance portion. 
By modifying as mentioned above, consumed electric power can be lowered and 
protection of the current protector can be improved. 
Prior art current protectors have patterns of electrical conductors as 
shown in FIGS. 5A to 5C. 
The pattern shown in FIG. 5A is a generally used pattern having a narrow 
portion therein, which does not blow near a rated current due to great 
heat dissipation but instantly blows by over-current due to rapid 
temperature rise adiabaticly only in the narrow portion. 
The patterns shown in FIGS. 5B and 5C are used for low rated current and 
have a long conductor with a uniform width so as to have a large 
resistance value and a large heat release value, resulting in blowing even 
by a low current. 
In order to reduce consumed electric power in the protective circuit, a 
current protector consuming a small amount of electric power has strongly 
been demanded. According to the pattern shown in FIG. 5A, since the 
released heat from the narrow portion is great, it is impossible to use 
such a pattern for low rated current type which has a small heat 
generation. On the other hand, the patterns shown in FIGS. 5B and 5C 
consume a large electric power due to large resistance value. Further, 
according to the patterns of FIGS. 5B and 5C, since the pattern as a whole 
is heated, remarkable smoking takes place when the patterns are formed on 
a resin-made substrate such as glass cloth-epoxy resin substrate, 
resulting in destroying not only the current protector per se but also the 
printed circuit board mounting the current protector. 
According to the pattern shown in FIG. 1 of the present invention, such 
problems are solved. 
In the present invention, the central high resistance portion preferably 
has a resistance value in the range of 20 to 40% of the total resistance 
values of the high resistance portions. 
Such a conductor pattern can be formed by etching of a metal foil or 
plating of a metal. As the material for the electrical conductor, the use 
of copper is preferable economically. 
In FIG. 1, the numeral 2 denotes a conductive terminal, and the current 
protector 1 comprises a conductor pattern 3 formed on an organic 
resin-made insulating substrate 4, the shape of the electrical conductor 
being formed by narrowing the width of a linear conductor partly so as to 
give three or more odd number of high resistance portions 3-a and low 
resistance portions 3-b placed between the high resistance portions. One 
of the high resistance portions 3-a is positioned in the center of the 
pattern 3, and other high resistance portions are positioned symmetrically 
with regard to the central high resistance portion (3-a).sub.c. Apart from 
FIG. 1, a plurality of high resistance portions 3-a can be used so long as 
being positioned symmetrically with regard to the central high resistance 
portion. 
The thickness of the conductor pattern is 3 to 8 .mu.m, the width of the 
conductor at the high resistance portion is preferably 30 to 70 .mu.m, and 
the length of one high resistance portion is preferably 100 to 300 .mu.m. 
As to the low resistance portion 3-b, the width is preferably 150 to 200 
.mu.m, and the length of one low resistance portion is 200 to 400 .mu.m. 
It is preferable to make the resistance value of the central high 
resistance portion (3-a).sub.c 20 to 40% of the total resistance values of 
the high resistance portions 3-a. When the resistance value is smaller 
than the above-mentioned range, clearing current becomes larger than the 
specified value and cannot protect the circuit. When the resistance value 
becomes too large, clearing current becomes smaller than the specified 
value and cannot supply electric power to the circuit, or the element acts 
as a resistor, not as a current protector, resulting in sometimes 
abnormally operating the circuit for a power supply. 
The current protector 1 can preferably be covered with an incombustible 
resin. 
By forming the conductor pattern as shown in FIG. 1, the temperature of the 
central high resistance portion (3-a).sub.c at the time of passing an 
electric current becomes the highest as shown in FIG. 2. Thus, when an 
over-current passes, blowing (or clearing) takes place without fail at the 
central high resistance portion (3-a).sub.c. 
Further, when the resistance value of high resistance portions 3-a other 
than central portion is made higher than that of the central high 
resistance portion (3-a).sub.c, the central high resistance portion 
(3-a).sub.c easily blows due to smaller heat dissipation. In contrast, 
when the resistance value of high resistance portions 3-a other than 
central portion is made lower than that of the central high resistance 
portion (3-a).sub.c, the central high resistance portion (3-a).sub.c is 
difficult to blow due to greater heat dissipation. Thus, the clearing (or 
blowing) characteristics can be controlled by changing the resistance 
value of high resistance portions 3-a other than the central portion 
positioned symmetrically with regard to the central high resistance 
portion (3-a).sub.c. 
Second modification! 
The current protector having the structure as mention above can be modified 
in that in the form of a chip-type current protector, the electrical 
conductor is formed on the insulating substrate and covered with a 
fluorine resin layer having a thickness of preferably 40 to 200 .mu.m. 
By modifying as mentioned above, the resulting current protector is further 
improved in the accuracy for forming the electrical conductor (thickness 
and width of the conductor). 
As the fluorine resin, there can be used those used for forming the 
insulating substrate. When the thickness of the fluorine resin is less 
than 40 .mu.m, the protection of the electrical conductor becomes 
insufficient, while when the thickness is more than 200 .mu.m, it is 
ineconomical. 
The above-mentioned current protector can be produced by the following 
Processes A and B. 
(Process A) 
The Process A comprises the steps of: 
a. drilling holes for connecting terminals in an organic resin-made 
insulating substrate on both sides of which metal foils are clad, one of 
the metal foils having a thickness of 3 to 8 .mu.m. 
b. forming a plating resist on portions of the insulating substrate other 
than portions for forming terminals, 
c. plating inside of the holes for connecting terminals and the portions 
for forming terminals to a necessary thickness, 
d. peeling the plating resist, 
e. forming an etching resist, 
f. forming in parallel a plurality of rows of a series of electrical 
conductors interposing terminals therebetween alternately on one side of 
the insulating substrate by etching the metal foil having the thickness of 
3 to 8 .mu.m, 
g. covering at least the surfaces of the electrical conductors with a 
fluorine resin in 40 to 200 .mu.m thickness, and 
h. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor (i.e. a fusible 
link). 
(Process B) 
The Process B comprises the steps of: 
a. drilling holes for connecting terminals in an organic resin-made 
insulating substrate on both sides of which metal foils are clad, at least 
one of the metal foils comprising a first copper layer having a thickness 
of 10 to 50 .mu.m, an intermediate layer of nickel or nickel alloy having 
a thickness of 1 .mu.m or less, and a second copper layer having a 
thickness of 3 to 8 .mu.m, and said second copper layer contacting with 
the insulating substrate, 
b. plating inside of the holes for connecting terminals to a necessary 
thickness, 
c. removing special portions of a plated layer and the first copper layer, 
d. removing the intermediate layer to expose the second copper layer, 
e. forming in parallel a plurality of rows of a series of electrical 
conductors interposing terminals therebetween alterately one side of the 
insulating substrate by etching the second copper layer by etching, 
f. covering at least the surfaces of the electrical conductors with a 
fluorine resin in 40 to 200 .mu.m, and 
g. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor. 
The resulting current protector chip is shown in FIG. 8, wherein numeral 22 
denotes the insulating substrate, numeral 26 denotes a terminal, and 
numeral 28 denotes the resin layer. 
FIG. 9 is a perspective view of the current protector chip of FIG. 8 after 
removing the resin layer 28. In FIG. 9, numeral 27 denotes an electrical 
conductor (i.e. fusible link). 
The fluorine resin layer can be formed by coating, printing or air spraying 
a suspension or solution of the fluorine resin according to conventional 
methods. It is also possible to press a fluorine resin film with heating. 
By covering the surface of electrical conductor (i.e. fusible link) with 
the fluorine resin, ignition and smoking of the current protector can be 
prevented more effectively. That is, the fluorine resin is remarkably 
incombustible and does not ignite nor burn in the air. Reason for this 
seems to be derived from the chemical structure of the fluorine resin per 
se. Since bonding between fluorine and carbon in the molecule is strong, 
the carbon is hardly eliminated from the molecule singly. Thus, the 
generation of smoke seems to be suppressed. On the other hand, a part of 
fluorine resin is decomposed at high temperatures to generate a colorless 
transparent gas including fluorine atoms by vaporization. Since the heat 
of vaporization is taken away from surroundings, more damage of the 
fluorine resin seems to be prevented. 
When a resin other than fluorine resin is used in the organic resin-made 
insulating substrate, such a resin is heated to an extremely high 
temperature at the blowing of the copper conductor (i.e. fusible link), 
resulting in generating a large amount of smoke for a long time, for 
example, several seconds. Thus, such a current protector is insufficient 
in function. In contrast, when the fluorine resin is used in the 
insulating substrate, such a problem is solved. On the other hand, the 
current protector is usually covered with a resin for protection. In a 
known method, there has been used a silicone resin (rubber), which is 
insufficient for suppressing smoking and ignition. In the present 
invention, smoking and generation of spark in the air can be suppressed by 
using the fluorine resin as a covering material. 
Third modification! 
The current protector having the structure as mentioned above can be 
modified in that in the form of a chip-type current protector, the 
electrical conductor is formed in the insulating substrate and sandwiched 
by a pair of light-shielding metal foils. 
By modifying as mentioned above, the resulting current protector is further 
improved in surface appearance as well as prevention of transmittance of 
light at the time of clearing or blowing. 
When the organic resin-made insulating substrate is laminated and adhered 
to, the fluorine resin used in the insulating substrate is softened again 
and provides a problem of insufficiency in dimensional accuracy at the 
production of small-sized chip-type current protectors. In such a case, it 
is desirable to use a resin having a lower softening point than the resin 
used in the insulating substrate on which an electrical conductor is 
formed and to conduct lamination and adhesion at a temperature at which 
the dimensional accuracy is allowable. As the adhesive for such a purpose, 
there can be used a tetrafluoroethylene-ethylene copolymer which is 
relatively cheap, and polytetrafluoroethylene which has a lower molding 
temperature. More concretely, by using polytetrafluoroethylene as the 
insulating substrate and a tetrafluoroethylene-ethylene copolymer as the 
adhesive, the above-mentioned purpose can be attained. 
As the light-shielding metal foil, there can be used conventional materials 
so long as the ignition, smoking and light at the time of blowing under 
over-current conditions can be prevented or shielded. The thickness and 
size of the light-shielding metal foil can be determined depending on the 
purpose and easiness of production, preferably 5 to 50 .mu.m in thickness 
and larger in size so long as not contacting with the terminals. 
The above-mentioned current protector can be produced by the following 
Processes C and D. 
(Process C) 
The Process C comprises the steps of: 
a. forming an article having electrical conductors which are formed by 
etching one of metal foils clad on both sides of an insulating substrate, 
b. laminating the article having electrical conductors, a fluorine 
resin-made prepreg or a fluorine resin-made film, and a metal foil, 
followed by adhesion so as to have the metal foils at the outmost 
surfaces, 
c. removing the metal foils of the resulting laminate except for special 
portions by etching to form light-shielding metal foil portions, 
d. laminating the etched article, a fluorine resin-made prepreg or a 
fluorine resin-made film, and a metal foil, followed by adhesion so as to 
have the metal foils at the outmost surfaces, 
e. drilling holes for connecting terminals, 
f. conducting plating so as to have conductors in the holes for connecting 
terminals, 
g. forming conductive terminals by etching, and 
h. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor (i.e. a fusible 
link). 
(Process D) 
The Process D comprises the steps of: 
a. forming an article having electrical conductors on one side by etching 
of one of metal foils clad on an insulating substrate, followed by 
formation of a light-shielding metal foil on another side of the article, 
b. forming a light-shielding metal foil by etching one of metal foils clad 
on another insulating substrate to give an insulating substrate having a 
light-shielding metal foil on one side, 
c. laminating a metal foil, the article having the light-shielding metal 
foil on one side and the electric conductors on another side, and a 
fluorine resin-made prepreg on a fluorine resin-made film, and the 
insulating substrate having the light-shielding metal foil on one side, 
followed by adhesion so as to have the metal foils at the outmost 
surfaces, 
d. drilling holes for connecting terminals in the resulting laminate, 
e. conducting plating so as to have conductors in the holes for connecting 
terminals, 
f. forming conductive terminals by etching, and 
g. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive, terminals 
at both ends interconnected by the electrical conductor (i.e. a fusible 
link). 
The resulting current protector chip is shown in FIG. 11, wherein numeral 
32 denotes the insulating substrate, and numeral 39 denotes a conductive 
terminal. 
When the electrical conductor has the thickness of 3 to 8 .mu.m, there is a 
problem in that cracks are easily produced at boundary between the 
connecting portion of terminal and the electric conductor due to thermal 
stress. Thus, when the current protector is used under circumstances with 
a large temperature difference, it is desirable to make the thickness of 
the conductive terminal connecting to the electrical conductor 10 .mu.m or 
more by partial plating or the like. But too thick terminals cause an 
increase of production cost and poor moldability at the time of 
lamination, followed by adhesion. Thus, the thickness can be 50 .mu.m at 
most. 
According to the third modification, the light-shielding metal foils 
sandwich the electric conductor (i.e. fusible link), so that ignition and 
smoking under over-current conditions can be prevented effectively by the 
light-shielding metal foils. When a fluorine resin is used in the 
insulating substrate, since the electrical conductor is buried in the 
insulating substrate, the current protector is hardly damaged and hardly 
generates smoke. 
Heretofore, when the covering resin layer is thin, e.g. less than 50 .mu.m, 
or when a fine organic foreign body adheres even if the covering resin 
layer is 50 .mu.m or more, there is a problem of damaging of the covering 
resin layer. Further, when the applied voltage is high, light emission 
caused by spark due to electric discharge in the insulating substrate is 
observed through the insulating substrate or covering resin layer, 
resulting in causing a problem of poor surface appearance. 
According to the present invention, since the light-shielding metal foils 
are used in the current protector, the above-mentioned problems are 
solved. 
Fourth modification! 
The current protector having the structure as mentioned above can be 
modified in that in the form of a chip-type current protector, the 
insulating substrate is made from a fluorine resin, and when the 
electrical conductor is formed on the insulating substrate, it is covered 
with a fluorine resin. 
By the modification as mentioned above, the resulting current protector is 
further improved in accuracy for forming electrical conductors (thickness 
and width of electrical conductors) and reliability for a long period of 
time even under circumstances having a large temperature change. 
The above-mentioned current protector can be produced by the following 
Processes E to H. 
(Process E) 
The Process E comprises the steps of: 
a. forming a plurality of electrical conductors by etching one of metal 
foils clad on both sides of a fluorine resin-made insulating substrate, 
said metal foil to be etched having a thickness of 3 to 8 .mu.m, 
b. laminating an article having the electrical conductors thereon, a 
fluorine resin-made prepreg or a fluorine resin-made film, and a metal 
foil, followed by adhesion, 
c. drilling holes for connecting terminals, 
d. conducting plating so as to have conductors in the holes for connecting 
terminals, 
e. forming conductive terminals by etching, and 
f. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor (i.e. a fusible 
link). 
(Process F) 
The Process F comprises the steps of: 
a. forming a fluorine resin-made insulating substrate on both sides of 
which metal foils are clad, at least one of the metal foils comprising a 
first copper layer having a thickness of 10 to 50 .mu.m, an intermediate 
nickel or nickel alloy layer having a thickness of 1 .mu.m or less, and a 
second copper layer having a thickness of 3 to 8 .mu.m, said second copper 
layer contacting with the insulating substrate, 
b. etching the special portion of the first copper layer, 
c. removing the intermediate layer to expose the second copper layer, 
d. forming a plurality of electrical conductors on one side of the 
insulating substrate by etching the second copper layer, 
e. laminating an article having the electric conductors thereon, a fluorine 
resin-made prepreg or fluorine resin-made film, and a metal foil, followed 
by adhesion, 
f. drilling holes for connecting terminals, 
g. conducting plating so as to have conductors in the holes for connecting 
terminals, 
h. forming conductive terminals by etching, and 
i. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor (i.e. a fusible 
link). 
(Process G) 
The Process G comprises the steps of: 
a. drilling holes for connecting terminals in a fluorine resin-made 
insulating substrate on both sides of which metal foils are clad, one of 
the metal foils having a thickness of 3 to 8 .mu.m, 
b. forming a plating resist on portions of the insulating substrate other 
than portions for forming conductive terminals, and plating the conductive 
terminals and inside of the holes to a necessary thickness, 
c. forming a plurality of electric conductors on one side of the insulating 
substrate by etching the metal foil having the thickness of 3 to 8 .mu.m 
formed on the laminate, 
d. covering the surface of electric conductors with a fluorine resin layer, 
and 
e. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor (i.e. a fusible 
link). 
(Process H) 
The Process H comprises the steps of: 
a. drilling holes for connecting terminals in a fluorine resin-made 
insulating substrate on both sides of which metal foils are clad, at least 
one of the metal foils comprising a first copper layer having a thickness 
of 10 to 50 .mu.m, an intermediate layer of nickel or nickel alloy having 
a thickness of 1 .mu.m or less, and a second copper layer having a 
thickness of 3 to 8 .mu.m, said second copper layer contacting with the 
insulating substrate, 
b. plating inside of the holes for connecting terminals to a necessary 
thickness, 
c. etching special portions of the plating layer and the first copper 
layer, 
d. removing the intermediate layer to expose the second copper layer, 
e. forming a plurality of electrical conductors on one side of the fluorine 
resin-made insulating substrate by etching the second copper layer, 
f. covering the surfaces of electric conductors with a fluorine resin 
layer, and 
g. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor. 
The resulting current protectors can be shown by FIGS. 13A to 13C. 
According to prior art processes, electrical conductors are formed by a 
thick film method or a plating method. The thick film method includes a 
pattern printing method wherein the conductors are directly formed by a 
thick film obtained by screen printing; and a thick film etching method 
wherein after printing the whole surface, conductors are formed by 
etching. According to the pattern printing method, it is difficult to form 
fine patterns and uniform thickness. According to the thick film etching 
method, the accuracy of thickness is improved considerably but the 
thickness in the substrate varies considerably. Further, the accuracy is 
further lowered by etching. 
On the other hand, the plating method includes a panel plating method 
wherein after conducting electric plating on the whole surface of an 
insulating substrate, electrical conductors are formed by etching; a 
pattern plating method wherein after conducting underlying plating of 
ultra-thin film, a pattern is formed by electro plating; and a full 
additive method wherein the conductors are formed by electroless plating. 
According to the panel plating method and the pattern plating method, it 
is difficult to control the scattering of the thickness in the substrate 
within 20%. According to the full additive method, the thickness accuracy 
is satisfactory but the working time is long and complicated control is 
necessary in order to increase the thickness accuracy. 
In contract, according to the present invention, since the ultra-thin 
copper film or composite metal foil, each having a predetermined 
thickness, is used, the sufficient accuracy can be obtained without 
suffering from the problems of prior art mentioned above. Further, the 
change of thickness of metal foils between lots or within a lot is very 
small, resulting in improving the etching accuracy and the accuracy of the 
conductor width. By such effects, scattering of resistance values becomes 
small, resulting in providing current protectors having excellent clearing 
characteristics with small scattering of clearing characteristics under 
over-current conditions. 
Further, since it is not necessary to control the thickness of electrical 
conductors depending on changes in working conditions, the yield can be 
improved, resulting in lowering the production cost. 
In addition, since the fluorine resin is used in the insulating substrate 
and in the covering resin layer, the same advantages as explained in the 
second and third modifications can be obtained. 
Fifth modification! 
The current protector having the structure as mentioned above can be 
modified in that in the form of a chip-type current protector, a vacant 
space is formed between the electrical conductor and the resin layer 
placed thereon. 
By the modification as mentioned above, the resulting current protector is 
further improved in insulating resistance after blowing or clearing. 
When the electrical conductor is formed in the insulating substrate, the 
vacant space is formed between the electrical conductor and the resin 
layer contacting with the electrical conductor. 
When the electrical conductor is formed on the insulating substrate, the 
vacant space is formed between the electrical conductor and the resin 
layer covering the surface of the electrical conductor. 
The volume of the vacant space is sufficient when the vacant space can be 
formed by the swell of the resin layer. 
The above-mentioned current protector can be produced by the following 
Processes I to J. 
(Process I) 
The Process I comprises as follows. In a process for producing a chip-type 
current protector wherein electrical conductor is covered with a resin, or 
a resin and a reinforcing material, a vacant space is formed by passing a 
predetermined amount of current for a predetermined time through the 
electrical conductor between the electrical conductor and the overlying 
resin layer. 
(Process J) 
The Process J comprises the steps of: 
a. drilling holes for connecting terminals in an insulating substrate 
having metal foils on both sides thereof, 
b. conducting plating in the holes to a necessary thickness, 
c. forming a plurality of electrical conductors on one side of the 
insulating substrate by etching one of the metal foils, 
d. covering the surfaces of electrical conductors with a resin layer, and 
e. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor (i.e. a fusible 
link). 
(Process K) 
The Process K comprises the steps of: 
a. forming an article having electrical conductors which are formed by 
etching one of metal foils clad on both sides of an insulating substrate, 
b. laminating the article having electrical conductors, a fluorine 
resin-made prepreg or a fluorine resin-made film, and a metal foil, 
followed by adhesion so as to have the metal foils at the outmost 
surfaces, 
c. drilling holes for connecting terminal in the resulting laminate, 
d. conducting plating so as to make conductors in the holes for connecting 
terminals, 
e. forming conductive terminals by etching, and 
f. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor (i.e. a fusible 
link). 
The resulting current protector chip is shown in FIGS. 15 and 16, wherein 
numeral 42 denotes an insulating substrate, numeral 44 denotes a 
conductive terminal, numeral 200 denotes a resin layer covering the 
surface, and numeral 201 denotes swelling. 
The resin layer can be formed in the same manner as described in the second 
modification. 
After this, the electric conductor is heated by passing an electric current 
therethrough to generate swelling of the covering resin layer. When the 
current value is too small, the necessary swelling does not take place, 
while the current value is too large, the electrical conductor blows. 
Therefore, it is preferable to pass an electric current so as to bring 
about the necessary swelling (preferably about 3 times as large as the 
rated electric current for 0.01 second or less) in several ten seconds and 
to have a sufficient time until blowing. Such a current changes depending 
on the kind of material, and thickness of the covering resin layer and the 
kind of material of the insulating substrate. 
In the present invention, the vacant spaces can be formed between both the 
upper and lower resin layers and the electrical conductor. 
The thickness of the conductive terminals and boundary portions between the 
conductive terminal and the electrical conductor is described in the third 
modification. 
According to the fifth modification, insulating properties after blowing 
are improved by forming the vacant spaces, in other words, by preventing 
adhesion of the covering resin layer from the electrical conductor by 
forming swelling of the resin layer. 
By forming the vacant spaces produced by swelling of the resin layer, the 
insulating resistance after blowing can be improved by (1) the covering 
resin layer is not directly exposed to the high temperature at the time of 
blowing, (2) the generation of carbonized product can be suppressed by the 
generation of carbon dioxide by the diffusion of oxygen in the air into 
the swelled portion, and (3) fine particles or evaporated product of metal 
diffuses into the swelled portion, resulting in reducing the residual 
amount in the blowed portion. 
In addition, the damage of the current protector can also be reduced 
effectively by not contacting directly with the blowed portion of the 
current protector by providing swelling to the covering resin layer. 
Needless to say, by using the fluorine resin in the insulating substrate 
and in the covering resin layer, the same advantages as described in the 
second, third and fourth modifications can be obtained. 
Sixth modification! 
The current protector having the structure as mentioned above can be 
modified in that in the form of a chip-type current protector, the 
electrical conductor is formed in the insulating substrate and a vacant 
space is formed at least a portion around the electrical conductor to be 
blowed. 
By modifying as mentioned above, the resulting current protector is further 
improved in accuracy for forming electrical conductors (thickness and 
width of electrical conductors) and reliability for a long period of time, 
and is high in insulation resistance after blowing. 
The above-mentioned current protector can be produced by the following 
Processes L and M. 
(Process L) 
The Process L comprises the steps of: 
a. forming a plurality of electrical conductors by etching one of metal 
foils clad on both sides of an organic resin-made insulating substrate, 
said metal foil to be etched having a thickness of 3 to 8 .mu.m, 
b. forming another insulating substrate having holes for forming vacant 
spaces in predetermined places, 
c. laminating the insulating substrate having a plurality of electrical 
conductors, the insulating substrate having holes for forming vacant 
spaces, and an insulating substrate having a metal foil on one side 
thereof so as to adjust the position of the holes for forming vacant 
spaces and the electrical conductors, followed by adhesion, 
d. forming holes for connecting terminals in the resulting laminate, 
e. conducting plating so as to form conductors in the holes for connecting 
terminals, 
f. forming conductive terminals by etching, and 
g. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor (i.e. a fusible 
link). 
(Process M) 
The Process M comprises the steps of: 
a. forming an organic resin-made insulating substrate on both sides of 
which metal foils are clad, at least one of the metal foils comprising a 
first copper layer having a thickness of 10 to 50 .mu.m, an intermediate 
nickel or nickel alloy layer having a thickness of 1 .mu.m or less, and a 
second copper layer having a thickness of 3 to 8 .mu.m, said second copper 
layer contacting with the insulating substrate, 
b. removing the first copper layer, 
c. removing the intermediate layer to expose the second copper layer, 
d. forming a plurality of electrical conductors on one side of the 
insulating substrate by etching the second copper layer, 
e. forming another insulating substrate having holes for forming vacant 
spaces in predetermined places, 
f. laminating the insulating substrate having a plurality of electrical 
conductors, the insulating substrate having holes for forming vacant 
spaces, and an insulating substrate having a metal foil on one side 
thereof so as to adjust the position of the holes for forming vacant 
spaces and the electrical conductors, followed by adhesion, 
g. drilling holes for connecting terminals in the resulting laminate, 
h. conducting plating so as to form conductors in the holes for connecting 
terminals, 
i. forming conductive terminals by etching, and 
j. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor (i.e. a fusible 
link). 
The resulting current protector chip has an appearance as shown in FIG. 11. 
The adhesion of the insulating substrate having holes for forming vacant 
spaces with other materials can be carried out, for example, by binding 
another insulating substrate with an insulating substrate having holes for 
forming vacant spaces and formed thereon a material having a lower 
softening point, or placing a resin film having a thickness of 3 to 30 
.mu.m, preferably 5 to 15 .mu.m and a softening temperature lower than 
that of an insulating substrate having holes between the insulating 
substrate having holes and another insulating substrate, followed by 
adhesion by the action of the inserted resin film. The above-mentioned two 
methods can be combined. That is, the material having a lower softening 
point is formed on the insulating substrate having the holes, and another 
insulating substrate is placed thereon via the resin film, followed by 
adhesion. In the latter case, the desirable thickness range mentioned 
above means the total thicknesses of the material having the lower 
softening point and the resin film. In the case of lamination with 
adhesion using the resin film, the resin film acts as a protective layer 
for the current protector, since the resin film covers the electrical 
conductors (i.e. fusible links). 
In the lamination with adhesion, it is preferable to use 
polytetrafluoroethylene as the insulating material and a 
tetrafluoroethylene-ethylene copolymer having a lower softening point than 
polytetrafluoroethylene as the adhesive, from the viewpoint of lowering 
the laminating and adhering temperature and reducing thermal stress in the 
laminate. 
In the sixth modification, the vacant space is formed on or around the 
electrical conductor (i.e. fusible link). The vacant space can hold air 
containing oxygen around the electrical conductor. When over-current 
passes, the generated heat oxidizes the electrical conductor rapidly to 
blow the conductor (fusible link). Further, when the air is present, the 
fluorine resin hardly produces a carbonized product, even if heated. Thus, 
an incombustible gas seems to be produced. When a fuse is heated in an 
airless state, i.e. in a fluorine resin, a carbonized product is formed 
from the fluorine resin. According to the sixth modification, the 
production of carbonized products can be prevented by the air held in the 
vacant space, and insulation resistance after blowing can be maintained at 
a sufficient high level. Thus, the current protector is very effective 
when high reliability of current protector is required. 
On the other hand, when a small amount of ambient substances such as vapor, 
sulfurous acid gas is included in the vacant space, for example, by 
penetration from interface of the substrate, the electrical conductor is 
eroded, resulting in changing the resistance value with the lapse of time, 
causing scattering of clearing characteristics. In such a case, the 
insertion of the resin film is recommended. 
Seventh modification! 
The current protector having the structure as mentioned above can be 
modified in that in the form of a chip-type current protector, the 
electrical conductor has a space or a non-adhesion portion with regard to 
the underlying insulating substrate. 
By modifying as mentioned above, the resulting current protector is further 
improved in accuracy for forming electrical conductors (thickness and 
width of electrical conductors) and reliability for a long period of time, 
and is high in insulation resistance after blowing. 
The above-mentioned current protector can be produced by the following 
Processes N and P. 
(Process N) 
The Process N comprises the steps of: 
a. forming a plurality of electrical conductors by etching one of metal 
foils clad on both sides of an organic resin-made insulating substrate, 
said metal foil to be etched having a thickness of 3 to 8 .mu.m, 
b. laminating the insulating substrate having electrical conductors 
thereon, an insulating material, and a metal foil, or laminating the 
insulating substrate having electrical conductors thereon and a metal 
foil-clad insulating material, and pressing for adhesion the laminated 
materials using a plate having holes so as not to press the special 
portions, 
c. drilling holes for connecting terminals in the resulting laminate, 
d. conducting plating so as to form conductors in the holes for connecting 
terminals, 
e. forming conductive terminals by etching, and 
f. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor. 
(Process P) 
The Process P comprises the steps of: 
a. forming an organic resin-made insulating substrate on both sides of 
which metal foils are clad, at least one of the metal foils comprising a 
first copper layer having a thickness of 10 to 50 .mu.m, an intermediate 
nickel or nickel alloy layer having a thickness of 1 .mu.m or less, and a 
second copper layer having a thickness of 3 to 8 .mu.m, said second copper 
layer contacting with the insulating substrate, 
b. removing the first copper layer, 
c. removing the intermediate layer to expose the second copper layer, 
d. forming a plurality of electric conductors on one side of the insulating 
substrate by etching the second copper layer, 
e. laminating the insulating substrate having electrical conductors 
thereon, an insulating material, and a metal foil, or laminating the 
insulating substrate having electrical conductors thereon and a metal 
foil-clad insulating material, and pressing for adhesion the laminated 
materials using a plate having holes so as not to press the special 
portions, 
f. drilling holes for connecting terminals in the resulting laminate, 
g. conducting plating so as to form conductors in the holes for connecting 
terminals, 
h. forming conductive terminals by etching, and 
i. cutting the center of the holes for connecting terminals so as to give a 
number of current protector chips, each chip having conductive terminals 
at both ends interconnected by the electrical conductor. 
The resulting current protector chip has an appearance as shown in FIG. 15. 
The adhesion of the insulating substrate having electrical conductors 
thereon with other insulating materials can be carried out by re-softening 
and melt-bonding of the fluorine resin used in the insulating substrate. 
It is also possible to insert a resin film having a lower softening point 
between the insulating substrate having the electrical conductors thereon 
and the other insulating materials and to conduct adhesion by this resin 
film. In this case, when the thickness of the resin film is too thick, 
there often takes place a phenomenon of adhesion due to a flow of the 
resin even in the portions not intended for adhesion without pressing the 
special portions at the time of lamination and adhesion. In order to 
prevent such a phenomenon, it is preferable to use the resin film having a 
thickness of 30 .mu.m or less, more preferably 15 .mu.m or less, and 5 
.mu.m or more, considering availability. 
When the insulating substrate having electrical conductors thereon is 
bonded via a material having a lower softening point in order to improve 
the dimensional accuracy for small-sized chips, it is preferable to use 
polytetrafluoroethyren as the insulating material and a 
tetrafluoroethylene-ethylene copolymer as an adhesive resin. 
In the seventh modification, the electrical conductors are kept from 
adhesion. Thus, it is possible to maintain air containing oxygen around 
the electrical conductor, resulting in oxidizing the fusible link 
(electrical conductor) rapidly to blow by the generated heat in the case 
of passing over-current. Further, when the air is present, the fluorine 
resin hardly produces a carbonized product even if heated, and an 
incombustible gas seems to be produced. Thus, the clearing characteristics 
become sensitive. 
The present invention is illustrated by the following Examples. 
In the Examples, the clearing test, the heat cycle test and measurement of 
resistance value were conducted as follows. 
Clearing Test! 
A rated current source, a resistance R (1-2 .OMEGA.) for measuring a 
current and a current protector to be measured were connected in series 
and both sides of the resistance were connected to an oscilloscope. After 
switching on the rated current source, wave forms were observed and a time 
of blowing (R) of the current protector was read on from the time scale 
(abscissae axis) of the oscilloscope. 
The current of this time was obtained by reading on the height of wave V 
from the voltage scale (ordinate axis) of the oscilloscope and calculating 
the following formula: 
EQU I(current)=V/R 
Heat cycle test! 
Condition 1: -40.degree. C. for minutes 
condition 2: 125.degree. C. for minutes 
After repeating the predetermined times (cycles) of Condition 1 and 
Condition 2 alternately, the thus treated sample was subjected to the 
measurement of a resistance value, which value was compared with the 
initial resistance value. 
Measurement of resistance value! 
A resistance value was measured by a so-called four terminal method. On an 
insulating substrate, both ends of a current protector to be measured were 
held between two metal rods standing on with the same distance as that of 
the terminals, and the two metal rods were held between probes for 
measuring. Then, a resistance value was measured. One probe was combined 
with two terminals while insulated, and a current was passed through one 
sample, while a voltage was measured in another sample. The current for 
measuring was 1 to 10 mA. 
EXAMPLE 1 
This Example is explained referring to FIGS. 3A to 3H. 
A metal foil 5 having a three layer structure as shown in FIG. 3A was 
prepared. In FIG. 3A, numeral 5-a denotes a first copper layer having a 
thickness of 15 .mu.m, numeral 5-b denotes an intermediate layer of Ni--P 
alloy having a thickness of 0.2 .mu.m, and numeral 5-c denotes a second 
copper layer having a thickness of 5 .mu.m. 
A substrate 4 was prepared by bonding the metal foil 5 to the substrate 4 
so as to contact the second copper layer 5-c to the substrate and also 
bonding a copper foil 5 having a thickness of 18 .mu.m on the other side 
as shown in FIG. 3B. 
A glass cloth-reinforced fluorine resin prepreg was used as a material for 
the substrate 4, and pressed under a pressure of 20 kgf/cm.sup.2 at 
385.degree. C. for 90 minutes for adhesion. 
Then, as shown in FIG. 3C, holes 6 with a diameter of 0.8 mm were drilled, 
and electroless plating was carried out to give conductors 7 having a 
thickness of 15 .mu.m as shown in FIG. 3D. 
After forming the copper plating coating 7, lands 2 to be formed into 
conductive terminals and having a diameter of 1.2 mm were formed around 
the holes 6. 
A photosensitive resist film 8 was laminated on the whole surfaces of the 
substrate 4 forming the copper plating coating 7, and a negative film (not 
shown in the drawings) for forming lands was adhered thereto, followed by 
exposure to light for curing. 
After removing the negative film, uncured portions of the photosensitive 
resist film were removed by development to form the resist film 8. 
Then, as shown in FIG. 3E, the first copper layer 5-a (copper plated in 15 
.mu.m thick) and the copper layer 5 of 18 .mu.m other than the land 
portion of the resist film 8 were removed using an alkaline etching 
solution. 
Then, the intermediate layer of Ni--P alloy 5-b was removed by etching 
using an etching solution containing nitric acid and hydrogen peroxide as 
major component as shown in FIG. 3F. Then, the cured photosensitive resist 
film 8 was peeled using a 5% by weight NaOH solution to form lands 2 which 
is to be formed into terminals. 
Then, a pattern 3 for current protector was formed. A photosensitive film 8 
was laminated using a laminator. Then, a negative film (not shown in the 
drawings) having transparent portions which have the same shape as the 
pattern was adhered thereon, followed by exposure to light. After removing 
the negative film, development, removal with etching, and peeling of the 
resist film were carried out to form the conductor pattern 3 on the 
substrate as shown in FIG. 3G. 
Then, on the thus formed conductor pattern 3 and upper exposed surface of 
the substrate 4, a silicone resin (SE-1700, a trade name, mfd. by Toray 
Dow Corning Co.) was coated in 60 .mu.m thickness and cured in an oven at 
130.degree. C. for 15 minutes to form a silicone protective film 9 as 
shown in FIG. 3H. 
The resulting substrate was cut with a diamond cutter at the center of the 
hole 6 so as to give individual current protector chips. 
The current protector chips had a resistance value of about 190 to 210 
m.OMEGA., with scattering of the resistance value within 10%. The blowing 
(clearing) times at the same current value was distributed within 10%. 
EXAMPLE 2 
A substrate 4 as shown in FIG. 4A was prepared by removing copper layers by 
etching the whole surfaces of a glass cloth-reinforced fluorine resin 
substrate. 
Holes 6 having a diameter of 0.8 mm were drilled as shown in FIG. 4B, 
followed by lamination of a photosensitive resist film 8 on both sides of 
the substrate, adhesion of positive type film (not shown in the drawing) 
for forming lands around the holes 6 on both sides, exposure to light and 
curing. 
Then, development was conducted to form a resist film 8 as shown in FIG. 
4C. 
After forming the resist film 8, electroless plating was carried out using 
the following composition under the following conditions to form lands 2 
as shown in FIG. 4D, wherein numeral 7 denotes an electroless plated 
coating: 
______________________________________ 
CuSO.sub.4.5H.sub.2 O 10 g/l, 
EDTA.4Na 40 g/l, 
pH 12.3 
37% CH.sub.2 O 3 ml/l, 
Additives for plating a small amount 
solution 
Temperature of plating 
70.degree. C. 
solution 
Thickness of plated film 
5 .mu.m 
______________________________________ 
After peeling the resist film 8, a photosensitive resist 8 was laminated on 
both sides of the substrate 4 again. On one side, a positive type film for 
the pattern (not shown in the drawing) was adhered between the lands, and 
on the other side, a film capable of exposed to light (not shown in the 
drawing) was adhered on the whole surface, followed by exposure to light. 
After carrying out development, resist films 8 as shown in FIG. 4E were 
formed. 
After forming the resist film 8, the conductor pattern 3 as shown in FIGS. 
4F and 4G were formed under the same electroless plating conditions as 
described in Example 1. 
After copper plating, the photosensitive resist film 8 was removed in the 
same manner as described in Example 1, followed by formation of a silicone 
protective film 9 on the upper portion of the pattern formed surface as 
shown in FIG. 4H. Current protector chips were obtained after cutting 
using a diamond cutter as described in Example 1. 
The resulting current protector chips showed the same resistance values and 
clearing characteristics as in Example 1. 
The resulting current protectors blow at the central high resistance 
portion under over-current without fail, so that there can be obtained 
current protectors having very stable clearing characteristics. Further, 
since the blowing takes place only at the central high resistance portion 
having a small area, damages of the substrate are small and there is no 
smoking. 
Further, since the clearing characteristics can be controlled only by 
changing the resistance values of high resistance portions other than the 
central high resistance portion, current protectors for low rated urrent 
type can easily be designed. 
EXAMPLE 3 
A composite metal foil having a three-layer structure 100 as shown in FIG. 
6A was prepared. In FIG. 6A, numeral 101 denotes a first copper layer 
having a thickness of 15 .mu.m, numeral 102 denotes an intermediate layer 
of Ni--P alloy having a thickness of 0.2 .mu.m, and numeral 103 denotes a 
second copper layer having a thickness of 5 .mu.m. Such a composite metal 
foil is disclosed in U.S. Pat. No. 5,403,672. 
The composite metal foil was bonded to an insulating substrate 22 so as to 
contact the second copper layer to the insulating substrate and a copper 
foil 23 of 18 .mu.m thick was bonded to another side of the insulating 
substrate as shown in FIG. 6B. 
As the material for the insulating substrate, glass cloth-reinforced 
polytetrafluoroethylene prepreg was used. The pressing was conducted at 
380.degree. C. for 90 minutes under a pressure of 20 kgf/cm.sup.2. 
Holes 24 for connecting terminals were drilled as shown in FIG. 6C and 
plating was carried out to form plated coating 25 of 15 .mu.m thick as 
shown in FIG. 6D. 
The first copper layer (and the previously plated coating) except for the 
portions to be formed into terminals was removed as shown in FIG. 6E using 
an alkaline etching solution (an A-Process, a trade name, mfd. by Meltex 
Inc.) to form terminal portions 26. 
Then, as shown in FIG. 6F, using an etching solution having nitric acid and 
hydrogen peroxide as major components, the intermediate Ni--P alloy layer 
exposed by the etching of the first copper layer was removed. 
Then, the second copper layer was etched so as to form in parallel a 
plurality of rows of a series of electrical conductors interposing 
terminals therebetween alternately (FIG. 6G). 
On the surface of the thus treated substrate, a polytetrafluoroethylene 
film (Nitoflon film, a trade name, mfd. by Nitto Electric Industrial Co., 
Ltd.) having a thickness of 100 .mu.m and also having holes in the 
portions corresponding to terminals was laminated and pressed at 
380.degree. C. for 30 minutes under a pressure of 20 kgf/cm.sup.2 (see 
FIGS. 6H and 6I). In FIGS. 6G to 6I, numeral 27 denotes the electrical 
conductor, numeral 28 denotes the resin film, and numeral 29 denotes 
cutting lines for individual current protector chips. 
EXAMPLE 4 
Using the same materials and steps as described in Example 3, electrical 
conductors were formed. 
On the surface of the resulting substrate, a film of 
tetrafluoroethylene-perfluoroalkoxyethylene copolymer having a thickness 
of 50 .mu.m (Afron PFA, a trade name, mfd. by Asahi Kasei Kogyo K.K.) was 
laminated and pressed at 340.degree. C. for 30 minutes under a pressure of 
20 kgf/cm.sup.2. 
Comparative Example 1 
The process of Example 1 was repeated except for using a silicone rubber by 
screen printing in place of the polytetrafluoroethylene film by pressing 
with heating. 
EXAMPLE 5 
As shown in FIG. 7A, a composite metal foil 110 comprising an aluminum 
carrier 111 having a copper layer 112 of 5 .mu.m was prepared. 
An insulating substrate as shown in FIG. 7B was prepared by bonding the 
composite metal foil to a substrate 22 so as to contact the copper layer 
to the substrate, while bonding a copper foil 23 having a thickness of 18 
.mu.m to another side of the substrate. Then, the aluminum carrier was 
peeled off. 
The substrate 22 used was the same as that used in Example 3 and the same 
press conditions as used in Example 3 were used. 
Holes for connecting terminals were drilled as shown in FIG. 7D and a 
plating resist was formed except for portions for forming terminals as 
shown in FIG. 7E, followed by electroplating to give a coating of 15 .mu.m 
thick (drawings showing the formation of plating resist and peeling were 
omitted). 
Then, the ultra-thin copper layer was etched so as to form in parallel a 
plurality of rows of a series of lectrical conductors interposing 
terminals therebetween lternately (FIGS. 7F and 7G). 
On the surface of the resulting substrate, fron PFA film having a thickness 
of 50 .mu.m was laminated nd pressed at 340.degree. C. under a pressure of 
20 kgf/cm.sup.2 using a vacuum press (FIG. 7H). 
In FIGS. 7F to 7H, numeral 24 denotes the holes for connecting terminals, 
numeral 27 denotes the electric conductors, and numeral 28 denotes the 
resin film. 
The resulting substrate was cut with a diamond cutter so as to give 
individual current protector chips. 
The current protectors obtained by Examples 3 to and Comparative Example 1 
had the electrical conductor width of 0.05 mm and a resistance value of 
about 180 m.OMEGA.. 
Scattering of the resistance values was with 10%. 
The results of clearing test revealed that no smoking was observed at the 
time of blowing as to the current protectors of Examples 3 to 5, but 
smoking for 1 or 2 seconds was observed under current passing conditions 
for making the blowing time 30 seconds or more in Comparative Example 1. 
As explained above, the current protector chips of the second modification 
are excellent in suppressing ignition and smoking. Further, since a metal 
foil having a constant thickness is used when better accuracy is necessary 
for the electrical conductors, the accuracy of the thickness of the 
electrical conductors is good, resulting in improving the conductor width 
accuracy. Thus, the scattering of resistance values is very reduced and 
the clearing characteristics are excellent. 
EXAMPLE 6 
As shown in FIG. 10A, an insulating substrate was prepared by bonding a 
ultra-thin copper foil 31 on one side of a substrate 32 and bonding a 
copper foil 33 having a thickness of 18 .mu.m on another side of the 
substrate. 
As the substrate, there was used a glass cloth-reinforced 
polytetrafluoroethylene resin prepreg, and press conditions at 380.degree. 
C. for 90 minutes under a pressure of 20 kgf/cm.sup.2 were used. 
Electrical conductors were formed by etching the ultra-thin copper foil 
layer using a pattern wherein a plurality of rows were arranged in 
parallel, each row arranging in series electrical conductors 35 
interposing terminals 34 therebetween alternately (FIG. 10B). 
Then, a copper foil 33 formed on a polytetrafluoroethylene resin prepreg 32 
was laminated and bonded by pressing with heating (FIG. 10C). The copper 
foils were etched to remove unnecessary portions to give light-shielding 
metal foils 36 (FIG. 10D). 
A pair of substrate 32 having a copper foil 33 on one side thereof were 
laminated again and pressed with heating (FIG. 10E). 
Holes 37 for connecting terminals were formed (FIG. 10F) and plating was 
carried out to form plate coating 38 having a thickness of 15 .mu.m (FIG. 
10G). Terminals 39 were formed by etching (FIGS. 10H and 10I). In FIG. 
10I, numeral 40 denotes cutting lines for individual current protector 
chips. 
Comparative Example 2 
Using the same materials and steps as used in Example 6, an insulating 
substrate having an ultra-thin copper foil on one side was prepared, 
followed by formation of electric conductors by etching. 
Then, a substrate having a copper foil was laminated and pressed with 
heating, followed by drill of holes for connecting terminals and plating 
to give a coating of 15 .mu.m thick in the holes. Then, terminals were 
formed by etching. 
The thus produced substrates in Example 6 and Comparative Example 2 were 
cut to give current protector chips. 
The resulting current protector chips had the conductor width of 0.05 mm 
and the resistance value of about 180 m.OMEGA.. The scattering of 
resistance values was within 10%. 
The results of clearing test revealed that no light and no smoke were 
admitted in Example 6 at the blowing, while in Comparative Example 2, a 
bright light emission from the insulating substrate was observed at the 
time of blowing. This means that sparks at the time of blowing was 
observed through the insulating substrate. 
As mentioned above, by the use of light-shielding metal foils, the light 
emission caused by blowing is not observed. Needless to say, the current 
protector is also excellent in suppression of ignition and smoking. 
EXAMPLE 7 
An aluminum carrier having an ultra-thin copper foil having a thickness of 
5 .mu.m (FIG. 7A) was bonded to a substrate 22 on one side thereof, and a 
copper foil 23 having a thickness of 18 .mu.m was bonded to another side 
of the substrate 22 (FIG. 7B). Then, the aluminum carrier was peeled (FIG. 
7C). As the substrate 22, polytetrafluoroethylene resin prepreg was used 
and the pressing conditions were a temperature of 380.degree. C., a time 
of 90 minutes and a pressure of 20 kgf/cm.sup.2 for lamination and 
adhesion. Holes for connecting terminals were drilled (FIG. 7D), followed 
by formation of a resist on non-plation portions. Plating was carried out 
to give a coating 26 of 15 .mu.m on the terminal portions and in the 
holes. 
A pattern for electric conductors was formed by etching. The pattern had a 
plurality of rows of a series of electrical conductors interposing 
terminals there-between alternately (FIGS. 7F and 7G). On the surface the 
resulting substrate, a polytetrafluoroethylene resin film (Nitoflon film, 
a trade name, mfd. by Nitto Electric Industrial Co., Ltd.) having a 
thickness of 100 .mu.m and also having holes in the portions corresponding 
to terminals was laminated and pressed at 380.degree. C. for 30 minutes 
under a pressure of 20 kgf/cm.sup.2 (see FIGS. 6H and 7H) 
EXAMPLE 8 
A composite metal foil 100 having a three-layer structure as shown in FIG. 
6A was prepared. In FIG. 6A, numeral 101 denotes a first copper layer 
having a thickness of 15 .mu.m, numeral 102 denotes an intermediate Ni--P 
alloy layer having a thickness of 0.2 .mu.m, and numeral 103 denotes a 
second copper layer having a thickness of 5 .mu.m. The composite metal 
foil was bonded to an substrate 22 so as to contact the second copper 
layer to the substrate and a copper foil 23 of 18 .mu.m thick was bonded 
to another side of the substrate (FIG. 6B). 
As the material for the substrate, glass cloth-reinforced 
polytetrafluoroethylene resin prepreg was used. The pressing conditions 
were the same as described in Example 7. 
Holes 24 for connecting terminals were drilled (FIG. 6C) and plated coating 
25 of 15 .mu.m thick was formed (FIG. 6D). 
The first copper layer (and the previously plated coating) except for the 
portions to be formed into terminals was removed as shown in FIG. 6E using 
an alkaline etching solution (an A Process, a trade name, mfd. by Meltex 
Inc.) to form terminal portions 26. 
Then, as shown in FIG. 6F, using an etching solution having nitric acid and 
hydrogen peroxide as major components, the intermediate Ni--P alloy layer 
exposed by the etching of the first copper layer was removed. 
Then, the second copper layer was etched so as to form in parallel a 
plurality of rows of a series of electrical conductors interposing 
terminals therebetween alternately (FIGS. 6F and 6G). 
On the surface of the thus treated substrate, a 
tetrafluoroethylene-perfluoroalkoxyethylene copolymer film (Aflon PFA, a 
trade name, mfd. by Asahi Kasei Kogyo K.K.) having a thickness of 100 
.mu.m and also having holes in the portions corresponding to terminals was 
laminated and pressed at 340.degree. C. for minutes under a pressure of 20 
kgf/cm.sup.2 (FIGS. 6H and 6I). 
EXAMPLE 9 
In the same manner as described in Example 7, an insulating substrate 
having an ultra-thin copper film of 5 .mu.m thick on one side and a copper 
foil of 18 .mu.m thick on another side of the substrate (FIG. 7C). 
Holes 24 for connecting terminals were drilled (FIG. 7D), and a resist was 
formed on non-plated portions, followed by plating to give a coating 
having a thickness of 15 .mu.m on the electrode portions and in the holes. 
The pattern for electrical conductors having the same shape as in Examples 
7 and 8 was formed by etching (FIGS. 7E and 7G). On the resulting surface, 
a tetrafluoroethylene-ethylene copolymer film (Aflex COP film, a trade 
name, mfd. by Asahi Kasei Kogyo K.K.) having a thickness of 50 .mu.m and 
having holes in portions corresponding to the terminals was laminated and 
pressed with heating in the same manner as described in Example 7 (FIGS. 
6H and 7H). 
EXAMPLE 10 
Using a composite metal foil 100 having a three-layer structure, a metal 
foil-clad insulating substrate 21 was prepared in the same manner as 
described in Example 8 (FIG. 12B). 
Then, the first copper layer 101 except for special portions (portions for 
forming electrical conductors and terminals positioned on the same level) 
was removed by etching (FIG. 12C). Then, the intermediate layer 102 was 
removed to expose the second copper layer 103, followed by etching of the 
second copper layer to form a plurality of electrical conductors 27 (FIGS. 
12D and 12E). 
The resulting insulating substrate having electric conductors, a 
tetrafluoroethylene-ethylene copolymer film (Aflex COP film, a trade name, 
mfd. by Asahi Glass Co., Ltd.) having a thickness of 12 .mu.m, and an 
insulating substrate made from a glass cloth-reinforced 
polytetrafluoroethylene resin and having a copper foil on one side were 
laminated and bonded (FIG. 12F) (the film is omitted in the drawing). The 
pressing conditions were a temperature of 280.degree. C., a time of 30 
minutes, and a pressure of 20 kgf/cm.sup.2. 
Holes 24 for connecting terminals were drilled in the resulting laminate 
(FIG. 12G), conductors 25 were formed in the holes by plating (FIG. 12H), 
and conductive terminals 26 were formed by etching (FIG. 12I). 
Comparative Example 3 
A glass cloth-reinforced polytetrafluoroethylene resin-made substrate 
having copper foils on both sides thereof was subjected to drilling of 
holes for connecting terminals, etching of the whole surfaces of the 
copper foils, pretreatment of plating, and panel electric copper plating 
to deposit copper in 5 .mu.m thickness. Then, a pattern for electrical 
conductors was formed by etching in the same manner as described in 
Examples 7 to 9. Then, a silicone rubber was screen printed to cover the 
electrical conductors. 
The thus produced current protector chip-holding insulating substrates 
obtained in Examples 7 to 10 and Comparative Example 3 were cut at the 
center of the holes for connecting terminals to give a number of current 
protector chips. 
Each current protector chip had a conductor width of 0.05 mm and the 
resistance value of about 180 m.OMEGA.. 
The scattering of resistance values was within 10% in Examples 7 to 10, but 
was over 30% in Comparative Example 3. Further, in the clearing test, no 
smoke nor spark were admitted in Examples 7 to 10, but smoking for 1 to 2 
seconds was observed in Comparative Example 3 under the conditions of 
making the clear time 30 seconds or more. 
The current protectors, 20 samples for each Example, were subjected to the 
heat cycle test at -40.degree. C. and 125.degree. C. for 1000 cycles. 
After the test, the change of resistance value was within 10% in Examples 7 
to 10, and no disconnection was observed. 
In Comparative Example 3, disconnection was generated in 4 samples, and 
even if not disconnected, the resistance value changed remarkably. 
As mentioned above, by the fourth modification, there can be obtained 
current protector chips excellent in suppression of ignition and smoking, 
having improved reliability for a long period of time, and able to be 
blowed even at low electric current. 
EXAMPLE 11 
As shown in FIG. 14A, a composite metal foil 100 having a first copper 
layer 101 of 15 .mu.m thick, an intermediate layer 102 of Ni--P alloy of 
0.2 .mu.m thick and a second copper layer 103 of 5 .mu.m thick was 
prepared. 
The second copper layer of the composite metal foil was bonded to one side 
of an insulating substrate 42 and a copper foil 43 of 18 .mu.m was also 
bonded to another side of the substrate as shown in FIG. 14B. 
As the material for the substrate, a glass cloth-reinforced 
polytetrafluoroethylene resin prepreg was used. The pressing conditions 
were a temperature of 380.degree. C., a time of 90 minutes and a pressure 
of 20 kgf/cm.sup.2. 
As shown in FIG. 14C, unnecessary portions of the first copper layer were 
removed by using an etching solution (A Process, a trade name, mfd. by 
Meltex Inc.) to form terminals 44. 
Using an etching solution containing nitric acid and hydrogen peroxide as 
major components, the intermediate layer exposed by removal of the first 
copper layer was removed (FIG. 14D). 
Then, the second copper layer was etched so as to form in parallel a 
plurality of rows of a series of electrical conductors 45 interposing 
terminals 44 therebetween alternately (FIG. 14E). 
On the resulting surface, a polytetrafluoroethylene resin film 46 and a 
copper foil 43 were bonded with heating at 380.degree. C. for 40 minutes 
under a pressure of 20 kgf/cm.sup.2 (FIG. 14F). 
Holes 47 for connecting terminals were drilled (FIG. 14G) and plated 
coatings 48 of 15 .mu.m thick were formed by plating (FIG. 14H). 
Terminals 44 were formed by etching (FIG. 14I). 
Then, a voltage was applied to both ends of terminals connected in series 
through current protectors to pass an electric current of 1.2 A for 60 
seconds. 
As a result, slight vacant spaces 49 between the polytetrafluoroethylene 
resin film and the electric conductors were admitted (FIG. 14J). 
EXAMPLE 12 
The process of Example 11 was repeated except for using a 
tetrafluoroethylene-perfluoroalkoxyethylene copolymer film (Aflon PFA 
film, a trade name, mfd. by Asahi Kasei Kogyo K.K.) having a thickness of 
100 .mu.m in place of the polytetrafluoroethylene resin film used in 
Example 11 and changing the pressing conditions to a temperature of 
340.degree. C., a time of 30 minutes and a pressure of 20 kgf/cm.sup.2. 
After passing an electric current of 1.2 A for 60 seconds, slight vacant 
spaces were admitted between the PFA film and the electrical conductors as 
in Example 11. 
Reference Example 1 
Example 11 was repeated except for not passing the electric current. 
Reference Example 2 
Example 12 was repeated except for not passing the electric current. 
The thus produced current protector chip-holding insulating substrates 
obtained in Examples 11 and 12, and Reference Examples 1 and 2 were cut at 
the center of the holes for connecting terminals to give a number of 
current protector chips. 
Each current protector chip had a conductor width of 0.05 mm and the 
resistance value of about 180 m.OMEGA.. 
After subjecting to the clearing test, 20 samples of Example 11 and 20 
samples of Example 12 showed the resistance value of 10 megohms or more, 
and almost on the order of gigaohm. 
In Reference Examples 1 and 2, the resistance value after the clearing test 
was in the range of 50 kilohms to 500 megohms. 
No ignition nor smoking were observed in Examples 11 and 12, and Reference 
Examples 1 and 2. 
As explained above, the fifth modification gives excellent insulation 
properties after blowing as well as excellent in suppression of ignition 
and smoking. 
EXAMPLE 13 
As shown in FIG. 17A, an insulating substrate 120 having a ultra-thin 
copper foil of 5 .mu.m thick on one side and a copper foil of 18 .mu.m 
thick on the other side was prepared. 
As the material for the substrate, a glass cloth-reinforced 
polytetrafluoroethylene resin prepreg was used and the pressing conditions 
were a temperature of 380.degree. C., a time of 90 minutes, and a pressure 
of 20 kgf/cm.sup.2. 
A pattern for electrical conductors was formed by etching of the ultra-thin 
copper foil. The pattern had a plurality of rows of a series of electrical 
conductors 150 interposing terminals 140 therebetween alternately (FIG. 
17B). 
On the other hand, a two-sided copper-clad laminate (substrate 121) made of 
a glass cloth-reinforced polytetrafluoroethylene resin was subjected to 
etching of whole surfaces of both sides, followed by lamination of a 
tetrafluoroethylene-ethylene copolymer 122 (Alfex film, a trade name, mfd. 
by Asahi Glass Co., Ltd.) having a copper foil 130 on one side thereof on 
both sides of the substrate 121 and pressing at 280.degree. C. for 30 
minutes under a pressure of 20 kgf/cm.sup.2 (FIG. 17C). 
Holes 160 for forming vacant spaces were drilled (a diameter 1.2 mm) (FIG. 
17D), and the copper foils 130 on both sides were removed by etching to 
give an insulating material having holes for forming vacant spaces (FIG. 
17E). 
The substrate having the electric conductors (FIG. 17B), the insulating 
material having the holes (FIG. 17E) and an insulating plate made of a 
glass cloth-reinforced polytetrafluoroethylene resin and having a copper 
foil 130 on one side were laminated and pressed with heating (FIG. 17F). 
Holes 170 for connecting terminals were drilled, followed by formation of 
a plated coating 180 of 15 .mu.m thick in the holes (FIGS. 17G and 17H) 
Terminals 190 were formed by etching (FIG. 17I). 
EXAMPLE 14 
Using the same materials (e.g. FIG. 18A wherein numeral 140 denotes 
ultra-thin copper foil, numeral 130 denotes a copper foil, and numeral 120 
denotes a substrate) and the steps as in Example 13, a pattern for 
electrical conductors 150 and terminals 140 (FIG. 18B) was formed on 
insulating substrate. 
On the other hand, a glass cloth-reinforced polytetrafluoroethylene 
resin-made laminate having copper foils on both sides thereof was drilled 
to form holes 160 (diameter 1.2 mm) for forming vacant spaces, followed by 
removal of the copper foils by etching to give an insulating material 
having the holes (FIG. 18C). 
The insulating substrate 123 having the electrical conductors 150 thereon, 
the insulating material 121 having the vacant spaces 161 therein covered 
with a tetrafluoroethylene-ethylene copolymer film 124 (Aflex film, a 
trade name, mfd. by Asahi Glass Co., Ltd.) of 12 .mu.m thick, and a 
polytetrafluoroethylene resin-made insulating plate 123 having a copper 
foil 130 on one side thereof were laminated and pressed at 280.degree. C. 
for 30 minutes under a pressure of 20 kgf/cm.sup.2 (FIG. 18D). 
Holes 170 for connecting terminals were drilled (FIG. 18E), followed by 
formation of plated coating 180 of 15 .mu.m thick (FIG. 18F) and formation 
of terminals 190 by etching (FIG. 18G). 
EXAMPLE 15 
A composite metal foil 210 as shown in FIG. 19A having a first copper layer 
211 of 15 .mu.m thick, an intermediate layer 212 of Ni--P alloy of 0.2 
.mu.m thick and a second copper layer 213 of 5 .mu.m thick was prepared. 
An insulating substrate having the composite metal foil on one side so as 
to contact the second copper layer to an substrate 220 and a copper foil 
230 of 18 .mu.m on the other side of the substrate was prepared (FIG. 
19B). The lamination and bonding conditions were the same as those of 
Example 17 (see FIG. 17A). 
Special portions (for forming terminals 240) were removed from the first 
copper layer by etching (FIG. 19C). Then, the intermediate layer was 
removed to expose the second copper layer, followed by formation of a 
plurality of electric conductors 250 by etching of the second copper layer 
(FIGS. 19D and 19E). 
On the other hand, a glass cloth-reinforced polytetrafluoroethylene 
resin-made substrate 220 having holes 260 for forming vacant spaces was 
prepared (FIG. 19F). 
The insulating substrate having electrical conductors 250 thereon, the 
substrate having holes for forming vacant spaces and covered with a 
tetrafluoroethylene-ethylene copolymer film 221 of 12 .mu.m thick (Aflex 
film, a trade name, mfd. by Asahi Glass Co., Ltd.) on both sides thereof, 
and an insulating material 222 having a copper foil 230 on one side 
thereof were laminated so as to adjust the holes being positioned over the 
electrical conductors, respectively, and bonded at 280.degree. C. for 
minutes under a pressure of 20 kgf/cm.sup.2 (FIG. 19G). 
Holes 270 for connecting terminals were drilled in the resulting laminate 
(FIG. 19H), followed by plating (FIG. 19I, numeral 280 denotes a plated 
coating) to forming conductors in the holes and formation of terminals 290 
by etching (FIG. 19J). 
Reference Example 3 
The process of Example 14 was repeated except for not forming holes for 
vacant spaces in the substrate. 
The thus produced current protector chip-holding laminates obtained in 
Examples 13 to 15 and Reference Example 3 were cut to give a number of 
current protector chips. 
Each current protector chip had a conductor width of 0.05 mm and the 
resistance value of about 180 m.OMEGA.. 
After subjecting to the clearing test, 20 samples of Example 13 and 20 
samples of Example 14 showed the resistance value of 10 megohms or more, 
and almost on the order of gigaohm. 
In Reference Example 3, the resistance value after the clearing test was in 
the range of 50 kilohms to 500 megohms. 
No ignition nor smoking were observed in Examples 13 to 15 and Reference 
Example 3. 
As mentioned above, by forming the vacant spaces at least around the 
electric conductors, the reliability is improved for a long period of time 
and the insulation resistance is high after blowing. 
EXAMPLE 16 
An insulating substrate (FIG. 20A) was prepared by bonding a ultra-thin 
copper foil 51 of 5 .mu.m thick on one side of a substrate 52 and a copper 
foil 53 of 18 .mu.m thick on another side of the substrate. As the 
material for the substrate, a glass cloth-reinforced 
polytetrafluoroethylene resin prepreg was used and the pressing conditions 
were a temperature of 380.degree. C., a time of 90 minutes and a pressure 
of 20 kgf/cm.sup.2. 
A pattern for electrical conductors was formed by etching of the ultra-thin 
copper foil. The pattern had a plurality of rows of a series of electrical 
conductors 55 interposing terminals 54 therebetween alternately (FIG. 
20B). 
The insulating substrate having electrical conductors thereon, and a glass 
cloth-reinforced polytetrafluoroethylene resin-made substrate having a 
copper foil on one side thereof were laminated via a tetrafluoro-ethylene 
copolymer film (Aflex COP film, a trade name, mfd. by Asahi Glass Co., 
Ltd.) of 6 .mu.m thick and bonded. In this case, in order to not press the 
special portions 57 of the laminate (i.e. the portions to be formed into 
electrical conductors and therearound), a metal plate 56 having holes was 
used (FIG. 20C, the resin film of 6 .mu.m thick being omitted). 
Holes 58 for connecting terminals were drilled (FIG. 20D), followed by 
formation of plated coating 59 of 15 .mu.m (FIG. 20E). 
Terminals 60 were formed by etching (FIG. 20F). 
EXAMPLE 17 
A composite metal foil having a first copper layer of 15 .mu.m thick, an 
intermediate layer of Ni--P alloy of 0.2 .mu.m thick and a second copper 
layer of 5 .mu.m thick was prepared. 
An insulating substrate was prepared by bonding the composite metal foil so 
as to contact the second copper layer with one side of a substrate, and 
bonding a copper foil of 18 .mu.m thick to another side of the substrate 
in the same manner as described in Example 16. 
Then, the first copper layer was removed (the shape being the same as in 
FIG. 20A), followed by removal of the intermediate layer to expose the 
second copper layer. The second copper layer was subjected to etching to 
form a plurality of electrical conductors (the shape being the same as in 
FIG. 20B). 
The insulating substrate having electrical conductors thereon covered with 
a pair of a tetrafluoroethylene-ethylene copolymer film (Aflex film, a 
trade name, mfd. by Asahi Glass Co., Ltd.) of 12 .mu.m thick and a glass 
cloth-reinforced polytetrafluoroethylene resin-based substrate having a 
copper foil on one side thereof were laminated under a metal plate for 
pressing having holes so as not to press the special portions of the 
laminate, while adjusting the positions of the electrical conductors and 
the holes in the pressing metal plate, followed by pressing at 280.degree. 
C. for 30 minutes under a pressure of 20 kgf/cm.sup.2 (see FIG. 20C). 
The resulting laminate was subjected to drilling for forming holes for 
connecting terminals, plating for forming conductors in the holes and 
etching for forming terminals. 
Reference Example 4 
The process of Example 16 was repeated except for not using the metal plate 
for pressing having holes. 
The thus produced current protector chip-holding laminates obtained in 
Examples 16 and 17 and Reference Example 4 were cut to give a number of 
current protector chips. 
Each current protector chip had a conductor width of 0.05 mm and the 
resistance value of about 180 m.OMEGA.. The scattering of resistance 
values was within 10%. 
After subjecting to the clearing test, 20 samples of Example 16 and 20 
samples of Example 17 showed the resistance value of 10 megohms or more, 
and almost on the order of gigaohm. 
In Reference Example 4, the resistance value after the clearing test was in 
the range of 50 kilohms to 500 megohms. 
No ignition nor smoking were observed in Examples 16 and 17 and Reference 
Example 4. 
As mentioned above, by making electrical conductors have spaces or 
non-adhesion portions with regard to underlying substrate, there can be 
obtained current protectors improved in accuracy for forming electrical 
conductors and reliability for a long period of time, and are high in 
insulation resistance after blowing.