Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
1994-03-31
2001-04-17
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S038000, C528S028000, C524S726000, C524S860000, C427S387000, C428S447000, C428S448000
Reexamination Certificate
active
06218496
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polyimidesiloxanes having a high T
g
and a relatively low bonding temperature and to hot melt adhesives made therefrom, particularly in the form of tapes. In particular, it relates to polyimidesiloxanes made by reacting 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) or bis(3,4-dicarboxyphenyl)ether dianhydride, also known as oxydiphthalic anhydride (ODPA), with a siloxane-containing diamine and a mixture of at least two of the following diamines: 2,2-bis(4[4-aminophenoxy]phenyl)propane (BAPP), 2,2′-bis(4-aminophenyl)-1,4-diisopropylbenzene, also known as bis-aniline P (BAP), 3,3′-diaminophenylsulfone (APS), and 1,3′-bis(3-aminophenoxy)benzene (APB).
In the electronics industry, adhesive tapes are used for a variety of purposes such as, for example, bonding a metal lead frame to an integrated circuit chip. Such tapes, useful for LOC (lead on chip) attachments, are required to be of high purity, have excellent adhesive properties, and be easy to apply using mass production techniques.
In some of these applications, it is very desirable for the adhesive tape to have a T
g
in excess of about 200° C. so that a chip bonded with the adhesive tape remains rigid during wire bonding, as rigidity prevents the formation of weak bonds. At the same time, the temperature at which the tape bonds to a substrate should be relatively low to permit more rapid processing of the chips and cause less thermal stress and damage. (See U.S. Pat. No. 4,624,978.)
Normally, the requirements for a high T
g
and a relatively low bonding temperature are contradictory. That is, most polyimidesiloxanes have a bonding temperature at least 100° C. higher than their T
g
, and the higher the T
g
the greater will usually be the difference between the bonding temperature and the T
g
.
SUMMARY OF THE INVENTION
We have discovered that adhesive tapes made with BPDA or ODPA, a siloxane-containing diamine, and a mixture of at least two of the diamines BAPP, BAP, APS, and APB have T
g
's in excess of 200° C., and often in excess of 230° C., and a bonding temperature that is only 20 to less than 70 degrees higher than their T
g
. This is apparently due to a synergistic interaction between the diamines because the mixture of diamines produces a polyimidesiloxane having a smaller difference between the bonding temperature and the T
g
than does any of the diamines by itself. A synergistic interaction between the two diamines is also demonstrated by the fact that the peel strength of a polyimidesiloxane adhesive made with that mixture of diamines is higher than the peel strength of polyimidesiloxane adhesives made from any of the diamines by itself.
The unusual polyimidesiloxanes of this invention can be used to prepare one, two, or three-layer adhesive tapes. Because of the high T
g
and relatively low bonding temperature of these tapes and the fact that they do not evolve volatiles during use, the tapes are highly desirable for applications in the electronics industry.
DESCRIPTION OF THE INVENTION
The polyimidesiloxanes used in the process and product of this invention are not only fully imidized but are also thermoplastic and soluble in a solvent. The polyimidesiloxanes can be formed by reacting a dianhydride (BPDA, ODPA, or mixtures thereof) with at least two of the four diamines (BAPP, BAP, APS, and APB)—plus a diamine containing siloxane groups.
We have found only two dianhydrides, BPDA and ODPA, that result in polyimidesiloxanes having the unexpected property of a high T
g
and a relatively low bonding temperature. Mixtures of these two dianhydrides can also be used. The preferred dianhydride is BPDA because it results in adhesives having a higher T
g
and a higher peel strength.
We have further found that only mixtures of two or more non-siloxane containing diamines selected from BAPP, BAP, APS, and APB result in polyimidesiloxanes having the unexpected properties of higher T
g
and relatively low bonding temperatures. The diamines BAPP, APS, and APB in the mixture can be present in an amount of about 10 to about 90 mole % and the diamine BAP can be present in the mixture in an amount of about 10 to about 80 mole % (based on the mixture of these diamines). A preferred mixture is about 10 to about 90 mole % BAPP and about 10 to about 80 mole % BAP as; if more than 90 mole % BAPP is used, the T
g
of the polyimidesiloxane becomes unacceptably low and if more than about 80 mole % BAP is used the polyimidesiloxane becomes difficult to bond. With BAPP and BAP, the diamines are more preferably used in a proportion of about 20 to about 80 mole % BAPP to about 20 to about 80 mole % BAP; the maximum properties seem to be achieved at a 50:50 molar ratio. BAPP and BAP are the preferred diamines.
The siloxane-containing diamines can be either aromatic or non-aromatic, but non-aromatic diamines are preferred as they are more readily available. Examples of siloxane-containing diamines that can be used include diamines having the formula
where R and R
1
are mono and diradicals, respectively, each independently selected from a substituted or unsubstituted 1 to 12 carbon atom aliphatic group or a substituted or unsubstituted 6 to 10 carbon atom aromatic group. Examples of monoradicals include —CH
3
, —CF
3
, —CH═CH
2
, —(CH
2
)
n
CF
3
, —C
6
H
5
, —CF
3
—CHF—CF
3
, and
Examples of diradicals include —(CH
2
)
n
—, —(CF
2
)
n—
, —(CH
2
)
n
CF
2
— and —C
6
H
4
—, where n is 1 to 10. The siloxane diamines are herein denoted by the notation “G
m
”, where “m” is the same “m” that is in the above formula and can be 1 to 200, but is preferably 1 to 12.
The polyimidesiloxanes of this invention are made using approximately stoichiometric quantities of diamine and dianhydride as that generally results in the highest molecular weight polyimidesiloxane, but the equivalent ratio of dianhydride to diamine can range from about 1:2 to about 2:1. The diamine portion of the polyimidesiloxane of this invention is about 1 to about 30 mole % siloxane containing diamine and about 70 to about 99 mole % of the diamine mixture of two or more of BAPP, BAP, APS, and APB. If more siloxane containing diamine is used the T
g
is lower, and if less siloxane containing diamine is used the polyimidesiloxane is less soluble and less adhesive. Preferably, about 10 to about 20 mole % of the diamine portion is the siloxane-containing diamine and about 80 to about 90 mole % of the diamine portion is the mixture of BAPP, BAP, APS, and APB.
The polyimidesiloxanes of this invention are typically prepared by forming a solution of the dianhydride and the three or more diamines. It is preferable to also include about 1 to about 2 mole % of a soluble endcapping agent in this solution to keep the molecular weight uniform so that its properties and processing do not vary greatly from batch to batch. The endcapping agent is a compound that has only a single anhydride group or a single amine group. Preferably, it has only a single anhydride group. Examples of endcapping agents include phthalic anhydride (PA), alkyl and aryl substituted phthalic anhydrides, and polynuclear anhydrides such as 1,8-naphthalic anhydride. The preferred endcapping agent is phthalic anhydride (PA) because it is readily available and thermally stable.
The solvent used to form the solution of the dianhydride and diamines should also dissolve the polyimidesiloxane that is formed. Suitable solvents depend upon the particular composition of the polyimidesiloxane that is to be made and dissolved, but may include N-methylpyrrolidinone (NMP), diglyme, triglyme, cyclohexanone, cyclopentanone, dimethylacetamide, and mixtures of these solvents. The solvent preferably has a boiling point between 130 and 210° C. as lower boiling solvents may evaporate too readily from the completed tape and higher boiling solvents may be too difficult to remove from the tape. The solution of the polyimidesiloxane in the solvent can be any percent solids desired, but it is preferably about 10 to about 30 wt % solids as more
Rojstaczer Sergio R.
Rosenfeld Jerold C.
Tyrell John A.
Brookes Ann E.
Fuerle Richard D.
Moore Margaret G.
Occidental Chemical Corporation
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