【発明の詳細な説明】[Detailed description of the invention]
利用産業分野
この発明は、磁気ヘツド用多結晶セラミツクス
材料表面の精密研摩方法に係り、微細気孔、すな
わち、直径1μｍ以下のマイクロポアを有する磁
気ヘツド用多結晶セラミツクス材料表面を無孔化
できる研摩方法に関する。
背景技術
今日、磁気ヘツドは、オーデイオ用、VTR用
の各テープレコーダー、データーレコーダー、コ
ンピユーター用デイスク、ドラム等の磁気記録再
生用として多用されており、さらに今後は、オー
デイオ用、VTR用の磁気記録媒体のメタルテー
プ化やPCM記録方式化、あるいはコンピユータ
ーの高速、高記録密度化が進められている。そこ
で、かかる要求に対処するため、従来の巻線型バ
ルクヘツドにかえて、ICテクノロジーを用い、
容易にマルチトラツク化、狭トラツク化が可能な
薄膜磁気ヘツドが最適と考えられている。
この薄膜磁気ヘツドに使用する基板材料には、
ソフトフエライト等の軟質磁性材料あるいは
Al2O3−TiC系材料のような緻密化された非磁性
材料が使用され、熱間静水圧プレス法やホツトプ
レス法により製造されている。
薄膜磁気ヘツドの製造に際して、基板材料はそ
の上に所定のパターンを形成する必要から、すぐ
れた表面粗度を有すること、表面に気孔等の欠陥
の少ないことが要求されている。例えば、再生用
に用いられるMR型薄膜磁気ヘツドではエレメン
ト厚みが数100Åであり、基板表面粗度は50Å以
下に研摩されていることが必要である。
また、かかる表面粗度まで研摩加工されたもの
でも、加工に伴なう加工変質層が存在すると、材
料本来のバルク特性が満足されず、磁性材料の磁
気特性の劣化、非磁性材料に被着された薄膜の特
性劣化を来たすので、加工変質層の少ないことが
必要である。
さらには、材料面において、表面粗度が良好で
加工歪みの少ない基板材料であつても、研摩加工
により表面にマイクロポアが多数露出すると、今
日の薄膜磁気ヘツドのパターンの微細化やマルチ
トラツク化に伴ない、製造上および磁気ヘツド特
性上の問題を生じる。すなわち、マイクロポア部
においてコンダクターの断線や短絡の恐れがあ
り、MR型磁気ヘツドではストライプ幅が数μｍ
程度であるため再生出力の低下が懸念され、ま
た、該ポア近傍では残留歪が存在して不均一な応
力場が形成され、その上に形成される磁性膜への
歪み転写の恐れがある。
従来技術の問題点
従来、薄膜磁気ヘツド基板材料の研摩には、ダ
イヤモンドポリツシユ法、メカノケミカルポリツ
シユ法（以下MCP法という）が適用されていた。
ダイヤモンドポリツシユ法は、粒径1μｍ程度
のダイヤモンドパウダーを用いてラツピング加工
するものであり、加工に際して端面だれ等がなく
形状精度誤差の少ない利点があるが、表面粗度が
数100Å程度しか得られず、加工変質層も100Å以
上残存する問題があつた。
また、MCP法は、被研摩材料より軟質で被研
摩材料と固相反応が促進されやすい微細粉を純水
に懸濁させた研摩液を用い、クロス等のポリシヤ
ーでラツプ加工するもので、被研摩材への加工歪
を抑制し、表面粗度も20Å程度の原子オーダーで
加工できる利点があり、加工歪が著しく少なく、
マイクロポアのきわめて少ないガラス材料や転位
などの格子欠陥の少ないSi、GGG、フエライト
等の単結晶材料には最適の研摩方法である。
ところが、このMCP法を、熱間静水圧プレス
法やホツトプレス法で得られた多結晶セラミツク
ス材料のごとき高密度ではあるがマイクロポアの
存在する基板に適用すると、同ポア近傍は不均一
な応力場が形成されているため、ケミカル効果に
より同ポア部が選択的にエツチングされやすく、
材料に内在するマイクロポアがバルク内部と同程
度に表面に露出してしまう問題があつた。また、
クロスをポリツシヤに用いると、ポア部のダレや
サイドエツチを生じ易く、マイクロポアの寸法も
実際以上に拡大されるという問題もあつた。
また、1μｍ以下のマイクロポアの内在する材
料を圧潰により完全に破壊し、マイクロポアを低
減させることは困難であり、またこの発明の荷重
範囲より大きな荷重を必要とし、加工表面にはよ
り大きな変質層が残留し、磁気ヘツド用基板とし
ては、実用上問題があつた。
発明の目的
この発明は、直径1μｍ以下のマイクロポアを
有する磁気ヘツド用多結晶セラミツクス材料の精
密研摩方法を目的とし、表面粗度50Å以下、加工
変質層厚み100Å以下の精密平面が得られ、かつ
材料表面のマイクロポアの露出を防止し、事実上
無孔化できる研摩方法を目的としている。
発明の概要
この発明は、マイクロポアの存在する磁気ヘツ
ド用多結晶セラミツクス材料表面を、
該材料より高硬度で粒径が0.08μｍ〜0.5μｍの
ダイヤモンド微粉末を２次凝集しないように純水
に分散させて研摩液とし、
Sn、Pb、はんだのいずれかをポリツシヤとし
てラツプ荷重1.0Kg／cm2〜２Kg／cm2で加圧回転さ
せて研摩を施し、
該材料表面に塑性流動層を形成させ、基板表面
のマイクロポアを低減させることを特徴とする磁
気ヘツド用多結晶セラミツクス材料の無孔化研摩
方法である。
発明の構成
この発明は、マイクロポアを有する磁気ヘツド
用多結晶セラミツクス材料の精密研摩に最適で、
加工歪が少なくMCP法と同程度の表面粗度が得
られかつマイクロポアを減少させることができる
ものであり、本発明研摩方法は次の研摩機構によ
ると考えられる。
すなわち、一般に、多結晶セラミツクス材料の
引掻きによる破壊現象は脆性破壊現象を伴なうも
ので、極微細パウダーによる多結晶セラミツクス
の高圧ラツプの場合は、有効砥粒先端とワークの
間は超高圧的な作用が働いていると思われ、接触
部表面は脆性から延性的な挙動を示す遷移点の状
態になり、塑性変形を伴なう破壊が進行し、塑性
流動層が存在する表面形成が行なわれ、研摩加工
が進行するものと考えられる。
以上の作用により、表面層に存在するマイクロ
ポアは圧壊された状態になり、研摩表面のマイク
ロポアはバルクに比べて著しく低減されるのであ
る。
発明の好ましい実施態様
この発明において、研摩液に分散させる微粉末
砥粒は、上記の塑性流動の考えから、砥粒と被研
摩材料の加工点の温度より高い融点を持ち、その
温度における強度、すなわち硬度が被研摩材料の
硬度より高いものが効果的に作用するため、研摩
する多結晶セラミツクス材料の融点と硬度に応じ
て、ダイヤモンドの分散量を適宜選定する。
また、上記砥粒の粒径が0.5μｍを越えると、加
工時の加工除去単位が大きくなり、塑性流動層厚
みが大きくなるため、表面粗度が粗く、加工変質
層厚みも増すので好ましくない。また、0.08μｍ
未満では加工能率が低く、実生産には好ましくな
い。
また、純水への分散効果を高めるため、グリコ
ール、ロート油あるいはヘキサメタリン酸ソーダ
を５％以下添加すると、２次凝集や被研摩材への
パウダーの溶着が防止されて表面粗度が向上す
る。
さらに、研摩液のPHを６〜８に管理して、被研
摩材とのケミカル反応を抑制することにより、マ
イクロポアの低減化が向上する。
ポリツシヤーの材質は、Sn、Pb、はんだの中
から被研摩材材質に応じて適宜選定すればよい。
また、この発明の研摩おけるラツプ圧力条件
は、従来のダイヤモンドポリツシユよりも高圧で
行なうことを特徴とし、1.0Kg／cm2以上の圧力に
よつて、ポリツシヤーへの砥粒の埋め込み深さが
1.0Kg／cm2未満の低荷重に比べて十分深くなり、
埋め込みが均一となり、砥粒の転動性も安定し、
表面は機械的な引掻ききずの集積された状態とな
るが、きず深さの低減が可能で、50Å以下の表面
粗度が得られる。また、２Kg／cm2を越える荷重
は、ポリツシング装置の剛性確保、回転精度が得
難いことから、1.0〜２Kg／cm2のラツプ圧力とす
る。
実施例
被研摩材には、熱間静水圧プレス法で高密度化
した50×50×１mmのAl2O3（融点2015℃、硬度
2000Hv）を用いた。この被研摩材のマイクロポ
ア数は、106ケ／cm2であつた。
研摩液は、粒径0.1μｍのダイヤモンド（3700
℃、10000Hv）微粉末を純水中に0.2wt％分散さ
せ、さらに、ヘキサメタリン酸ソーダを1wt％添
加した。
ポリツシヤには350mmφのPb盤を用い、ポリツ
シヤ表面に被研摩材を当接させ、両者を相対的に
回転させて研摩した。このとき、1.2Kg／cm2のラ
ツプ荷重をかけ、40rpmで回転させ、200c.c.／hr
の割合で研摩液を連続添加した。（本発明Ａ）
また、比較のため、上記の本発明Ａ、Ｃと同じ
セラミツクを被研摩材とし、SiO2（1610℃、
1000Hv）砥粒を使用して第１表の研摩条件で
MCP法（比較例Ｄ）を行なつた。
上記２種の被研摩材の研摩状態を、表面段差測
定器（Talystep、stylus 0.1μｍＲ）で表面粗度
を測定し、偏光解析装置を使用して、MCP面と
の相対加工変質層厚みを測定し、更に微粉干渉式
顕微鏡でマイクロポア数をカウントし、第１表に
示す測定結果を得た。
第１表の研摩結果比較表から明らかなように、
この発明による研摩（本発明Ａ）によつて、多結
晶セラミツクス材料は従来のMCP法（比較例Ｂ、
Ｄ）と同程度の表面粗度が得られている。
また、加工変質層はMCP法より多いが、従来
のダイヤモンドポリツシユ面（比較例Ｃ）に比べ
て著しく減少している。
さらに、マイクロポア数は、MCP法の場合が
バルクのポア数と同程度であるのに対して、桁数
が１桁異なるほど著しく低減されているのが分か
る。
以上の如く、この発明による研摩方法は、マイ
クロポアの存在する磁気ヘツド用多結晶セラミツ
クス材料を、表面粗度50Å以下、加工変質層厚み
100Å以下の精密平面に加工でき、しかも、表面
のマイクロポアの露出が防止されて事実上無孔状
態が得られる。したがつて、この発明の研摩方法
で研摩した基板を薄膜磁気ヘツドに使用すると、
信頼性、歩留、電磁変換特性の向上に大きな効果
が得られる。
Field of Application This invention relates to a precision polishing method for the surface of a polycrystalline ceramic material for a magnetic head, and is a polishing method that can make the surface of a polycrystalline ceramic material for a magnetic head having fine pores, that is, micropores with a diameter of 1 μm or less, non-porous. Regarding. BACKGROUND ART Today, magnetic heads are widely used for magnetic recording and reproduction in audio and VTR tape recorders, data recorders, computer disks, drums, etc. Progress is being made in the use of metal tape and PCM recording media, and in computers with higher speeds and higher recording densities. Therefore, in order to meet these demands, we used IC technology instead of the conventional wire-wound bulkhead.
A thin-film magnetic head that can be easily multitracked and narrowed is considered to be optimal. The substrate materials used for this thin film magnetic head include:
Soft magnetic materials such as soft ferrite or
A densified non-magnetic material such as Al 2 O 3 -TiC-based material is used and manufactured by hot isostatic pressing or hot pressing. In manufacturing thin film magnetic heads, the substrate material is required to have excellent surface roughness and to have few defects such as pores on the surface because a predetermined pattern must be formed on the substrate material. For example, in an MR type thin film magnetic head used for reproduction, the element thickness is several hundred angstroms, and the substrate surface roughness must be polished to 50 angstroms or less. In addition, even if the surface has been polished to such a roughness, if there is a damaged layer due to processing, the original bulk properties of the material will not be satisfied, resulting in deterioration of the magnetic properties of magnetic materials and adhesion to non-magnetic materials. It is necessary to minimize the number of processed-altered layers, since this may cause deterioration of the properties of the thin film. Furthermore, in terms of materials, even if the substrate material has good surface roughness and low processing distortion, many micropores are exposed on the surface by polishing, which leads to the miniaturization of patterns and multitrack patterns in today's thin-film magnetic heads. This results in problems in manufacturing and magnetic head characteristics. In other words, there is a risk of disconnection or short-circuiting of the conductor in the micropore area, and in MR type magnetic heads, the stripe width is several μm.
Because of this, there is a concern that the reproduction output will decrease.Furthermore, residual strain exists near the pores, forming a non-uniform stress field, and there is a fear that the strain will be transferred to the magnetic film formed thereon. Problems with the Prior Art Conventionally, the diamond polishing method and the mechanochemical polishing method (hereinafter referred to as the MCP method) have been applied to polish thin film magnetic head substrate materials. The diamond polishing method uses diamond powder with a particle size of about 1 μm to perform lapping processing, and has the advantage of having no edge sagging during processing and less error in shape accuracy, but it can only obtain a surface roughness of about 100 Å. First, there was a problem that a process-affected layer of more than 100 Å remained. In addition, the MCP method uses a polishing liquid in which fine powder, which is softer than the material to be polished and tends to promote solid-phase reaction with the material to be polished, is suspended in pure water, and is lapped with a polisher such as a cloth. It has the advantage of suppressing processing distortion to the abrasive material and can process surface roughness on the atomic order of about 20 Å, resulting in significantly less processing distortion.
This is the best polishing method for glass materials with extremely few micropores and single crystal materials such as Si, GGG, and ferrite that have few lattice defects such as dislocations. However, when this MCP method is applied to a substrate with a high density of micropores, such as a polycrystalline ceramic material obtained by hot isostatic pressing or hot pressing, a nonuniform stress field is created in the vicinity of the pores. Because the pores are formed, the pores are easily etched selectively due to chemical effects.
There was a problem in that the micropores inherent in the material were exposed on the surface to the same extent as inside the bulk. Also,
When a cloth is used as a polisher, sag or side etch is likely to occur in the pore portion, and there is also the problem that the size of the micropores becomes larger than the actual size. In addition, it is difficult to completely destroy the material containing micropores of 1 μm or less by crushing and reduce the number of micropores, and it also requires a load larger than the load range of this invention, resulting in greater deterioration of the machined surface. This layer remained and caused a practical problem as a substrate for a magnetic head. Purpose of the Invention The object of the present invention is to provide a precision polishing method for a polycrystalline ceramic material for a magnetic head having micropores with a diameter of 1 μm or less, which provides a precision flat surface with a surface roughness of 50 Å or less and a process-affected layer thickness of 100 Å or less. The objective is to create a polishing method that prevents the exposure of micropores on the surface of the material and makes it virtually pore-free. SUMMARY OF THE INVENTION The present invention is based on the present invention, in which the surface of a polycrystalline ceramic material for a magnetic head containing micropores is soaked in pure water to prevent secondary agglomeration of fine diamond powder, which is harder than the material and has a particle size of 0.08 μm to 0.5 μm. The material is dispersed to form a polishing liquid, and polished by using either Sn, Pb, or solder as a polisher and rotating under pressure at a wrap load of 1.0 Kg/cm 2 to 2 Kg/cm 2 to form a plastic fluidized layer on the surface of the material. , a method for polishing a polycrystalline ceramic material for a magnetic head to make it pore-free, which is characterized by reducing micropores on the surface of a substrate. Structure of the Invention The present invention is ideal for precision polishing of polycrystalline ceramic materials for magnetic heads having micropores.
The polishing method of the present invention is thought to be based on the following polishing mechanism, which has less processing strain and can obtain a surface roughness comparable to that of the MCP method, and can reduce micropores. In other words, the fracture phenomenon caused by scratching of polycrystalline ceramic materials is generally accompanied by a brittle fracture phenomenon, and in the case of high-pressure lapping of polycrystalline ceramics using ultrafine powder, ultra-high pressure is applied between the effective abrasive grain tip and the workpiece. As a result, the contact surface enters a transition point state where it exhibits brittle to ductile behavior, and fracture accompanied by plastic deformation progresses, forming a surface with a plastic fluidized layer. It is thought that the polishing process progresses. Due to the above action, the micropores existing in the surface layer are crushed, and the number of micropores on the polished surface is significantly reduced compared to the bulk. Preferred Embodiment of the Invention In this invention, the fine powder abrasive grains to be dispersed in the polishing liquid have a melting point higher than the processing point temperature of the abrasive grains and the material to be polished, based on the above-mentioned idea of plastic flow, and have a high strength at that temperature. That is, since a diamond having a hardness higher than that of the material to be polished is effective, the amount of diamond dispersed is appropriately selected depending on the melting point and hardness of the polycrystalline ceramic material to be polished. Furthermore, if the grain size of the abrasive grains exceeds 0.5 μm, the unit of removal during processing becomes large and the thickness of the plastic fluidized layer becomes large, resulting in rough surface roughness and an increase in the thickness of the damaged layer due to processing, which is not preferable. Also, 0.08μm
If it is less than that, processing efficiency will be low and it is not preferable for actual production. Furthermore, in order to enhance the dispersion effect in pure water, adding 5% or less of glycol, funnel oil, or sodium hexametaphosphate prevents secondary agglomeration and welding of the powder to the material to be polished, thereby improving the surface roughness. Further, by controlling the pH of the polishing liquid to 6 to 8 and suppressing chemical reactions with the material to be polished, the reduction of micropores is improved. The material of the polisher may be appropriately selected from among Sn, Pb, and solder depending on the material of the material to be polished. In addition, the lapping pressure conditions in the polishing of this invention are characterized by being performed at a higher pressure than conventional diamond polishing, and by applying a pressure of 1.0 kg/cm 2 or more, the depth of embedding of the abrasive grains in the polisher is reduced.
It is sufficiently deep compared to a low load of less than 1.0Kg/ cm2 ,
The embedding is uniform and the rolling properties of the abrasive grains are stable.
Although the surface becomes a state where mechanical scratches are accumulated, the depth of the scratches can be reduced and a surface roughness of 50 Å or less can be obtained. In addition, if the load exceeds 2 kg/cm 2 , it is difficult to ensure the rigidity of the polishing device and the rotation accuracy, so the lap pressure is set at 1.0 to 2 kg/cm 2 . Example The material to be polished was 50 x 50 x 1 mm Al 2 O 3 (melting point 2015℃, hardness
2000Hv) was used. The number of micropores in this material to be polished was 10 6 /cm 2 . The polishing liquid was diamond (3700) with a particle size of 0.1 μm.
℃, 10000 Hv) fine powder was dispersed in pure water at 0.2 wt%, and further, 1 wt% of sodium hexametaphosphate was added. A 350 mmφ Pb disk was used as the polisher, and the material to be polished was brought into contact with the surface of the polisher, and the two were rotated relative to each other for polishing. At this time, apply a lap load of 1.2Kg/cm 2 , rotate at 40rpm, and 200c.c./hr.
The polishing fluid was continuously added at a rate of . (Invention A) For comparison, the same ceramic as in Inventions A and C was used as the material to be polished, and SiO 2 (1610°C,
1000Hv) using abrasive grains under the polishing conditions shown in Table 1.
The MCP method (Comparative Example D) was carried out. The polished state of the above two types of materials to be polished was measured by measuring the surface roughness using a surface step measuring device (Talystep, stylus 0.1μmR), and by using an ellipsometry device, measuring the thickness of the machining-affected layer relative to the MCP surface. Furthermore, the number of micropores was counted using a fine powder interference microscope, and the measurement results shown in Table 1 were obtained. As is clear from the comparison table of polishing results in Table 1,
By polishing according to the present invention (invention A), polycrystalline ceramic materials can be polished by the conventional MCP method (comparative example B,
A surface roughness comparable to that of D) was obtained. Furthermore, although the number of processed damaged layers is larger than that of the MCP method, it is significantly reduced compared to the conventional diamond polished surface (Comparative Example C). Further, it can be seen that the number of micropores is approximately the same as the number of pores in the bulk in the case of the MCP method, whereas it is significantly reduced as the number of micropores differs by one order of magnitude. As described above, the polishing method according to the present invention can polish a polycrystalline ceramic material for a magnetic head containing micropores with a surface roughness of 50 Å or less and a process-altered layer thickness.
It can be processed into a precision flat surface of 100 Å or less, and the exposure of micropores on the surface is prevented, resulting in a virtually pore-free state. Therefore, when a substrate polished by the polishing method of the present invention is used in a thin film magnetic head,
Great effects can be obtained in improving reliability, yield, and electromagnetic conversion characteristics.
【表】【table】
【表】【table】