Elimination of GMR Read/Write Sensor Corrosion in the Lapping Process with Additives to Lapping Slurry
Original Publication Date: 2001-Aug-01
Included in the Prior Art Database: 2003-Jun-20
In the manufacture of the GMR (giant magnetoresistive) magnetic recording heads, lapping is a very important process at which the read and write sensors are lapped to a precise thickness to arrive at a specified writing and reading performance. However, the currently-used lapping slurry is lacking a vital function of preventing read/write sensor corrosion during process. The signature of in process read sensor corrosion is a resistance increase over 1.5 ohms. The present invention discloses the use of benzotriazole (BTA) and a combination of benzotriazole and sodium borate in the lapping slurry to protect the metals in GMR heads during processing. It is also disclosed that it is important to remove sodium citrate from the slurry as it is corrosive to the metals. The following 3 cell experiment demonstrate the effectiveness of this invention. Cell one has 0.1% of BTA added to a commercial slurry mixture from Amplex, cell 2 has 0.1% BTA and 1.8% of sodium borate added to the same slurry and cell 3 is the currently used slurry with the composition of 1% of sodium citrate added to the Amplex slurry. Experimental data indicates that most of the jobs (some 800 sliders) in cell 1 have no resistance increase with a maximum of 2% of the sliders having over 1.5 ohm increase, cell 2 has a maximum of 3.4% of the sliders having 1.5 ohm increase in one job and every job in the control group has over 20% of the sliders having 1.5 ohm increase in resistance. While cell 2 does not appear to be as good as cell 1 in sequestering resistance increase and in-line corrosion, the lapping rate and thus the process time is similar to control and cell 1 has a 50% decrease in lapping rate. It is apparent that cell 1 and cell 2 have much lower resistance increase rate compared with control, other data also exist that demonstrate the advantage of the present invention.