Designing Suspension Gimbal for Hygroscopic Performance Improvement

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Berenice Doyle
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1 Designing Suspension Gimbal for Hygroscopic Performance Improvement K. C. Ee, Ph.D. Peter Hahn Magnecomp Precision Technology 1

2 Magnecomp Precision Technology A leading suspension manufacturer Subsidiary of TDK Operates manufacturing plants in Thailand at Wangnoi and Rojana, and in China at Dong-guan Has Technology Development functions in Wangnoi, Thailand and California, USA 2

3 Overview Static attitude (SA) of HGA (head gimbal assembly) needs to be stable under different temperature and humidity conditions for flying height control. For suspensions, the polyimide and coverlayer are hygroscopic materials which means material expands with higher humidity. Controlling humidity impact on suspension is important for SA stability. Finite element model was established to study the influence of humidity on PSA change. Its results will be discussed. Experiment was conducted on designs with different material properties. 3

4 Definition of Pitch Static Attitude (PSA) PSA is the angle between the slider surface and the suspension assembly datum plane at operating height. arm datum dimple -ve PSA suspension slider disk +ve PSA PSA during operating conditions is important as it affects the slider flying height, and thus impacts the read/write operations of HDD. 4

5 Effect of Temperature vs Humidity Temperature effect Δ PSA = deg for increase in temperature of 45 o C. Humidity effect Δ PSA = 0.32 deg for increase in relative humidity of 70%. Experimental data shows typically the humidity effect is three to seven times of the temperature effect. 5

6 Effect of Humidity Basic mechanisms of hygroscopic expansion on circuit structure. Hygroscopic material (eg, PI 10 um thick) Non-hygroscopic material (eg, Cu 12 um thick) (a) Hygroscopic material (eg, Coverlay 4 um thick) (b) For 2-layer structure, expansion of Pi layer is constrained by the metal layer, resulting in final shape of bending down when PI expands. (c) With added thin coverlay, the deformation is partially compensated. 6

FE Model Half model with symmetry Boundary Condition Fixed Boundary Condition for welds Z-disp = 0 for dimple contact Loadbeam Flexure SST Boundary conditions are defined

7 FE Model Half model with symmetry Boundary Condition Fixed Boundary Condition for welds Z-disp = 0 for dimple contact Loadbeam Flexure SST Boundary conditions are defined by: Dimple contact to the suspension loadbeam (stainless steel: SST) Points on flexure SST welded to the loadbeam Polyimide Coverlay Epoxy Cu Exploded view Slider Solder 7

8 Typical Modeling Results SST Strut Inside SST Circuit layers positive change direction for PSA 1. Assembly behaves similar to one-side-fixed Boundary Condition like a cantilever with the welding points fixing one end. 2. Expansion of the polyimide layer generally pulls the slider tip down into positive PSA direction. 8

Comparison of Different Design Styles SST Circuit layers SST strut outside Design case SST strut inside Pitch change: 0.32 deg Design case SST strut outside Pitch change: 0.80 deg 1.

9 Comparison of Different Design Styles SST Circuit layers SST strut outside Design case SST strut inside Pitch change: 0.32 deg Design case SST strut outside Pitch change: 0.80 deg 1. Compares Relative Humidity increase of 70%. 2. Simulation of alternative gimbal designs with SST Strut at outside and inside positions. 3. SST Outside construction shows a much larger response to humidity change for this particular design. 9

design at SJB/SBB area A more flexible design at SJB/SBB area

10 SJB/SBB Area Design Modification Nominal case with rigid SJB/SBB area Flexible SJB/SBB area here nominal Modified design at SJB/SBB area A more flexible design at SJB/SBB area tends to lower the PSA response to humidity change (~10% reduction). 10

11 Impact of Material Properties CHE SST Circuit layers Nominal 2X CHE coefficient For polyimide materials, CHE coefficient may vary widely (Typical CHE range: ppm/%rh). 11

12 Design Considerations Consideration factors for gimbal design Static Attitude (PSA,RSA) adjustment process Electrical performance (impedance, insertion loss, cross talk, etc) Lift-off consideration (trailing edge limiter design) Design Consideration Factors Gimbal stiffness (Kp, Kr, Kl, Kz) Take off touch down SJB/SBB process response Gimbal resonance 12

Case Studies SST on PI Base PI under SST SST on PI

connecting to SST strut Design RH2 base PI under SST

(5 um) PI at circuit strut Design RH4 PI openings

(unm/deg) Nominal 0.320 0.60 0.64 RH1 0.180 0.67 0.

13 Case Studies SST on PI Base PI under SST SST on PI Design RH1 with added SST on polyimide (PI), PI tab connecting to SST strut Design RH2 base PI under SST strut, SST island on Pi layer Design RH3 half thick (5 um) PI at circuit strut Design RH4 PI openings Design Modeled PSA Change (deg) KP (unm/deg) KR (unm/deg) Nominal RH RH RH RH

14 Modeling Results - Animation Pi under SST SST on Pi layer Constraint on Pi layer due to SST Results in local upward deformation and Thus lower the overall PSA change Nominal Design RH2 Design Modeled PSA Change (deg) Nominal RH Nominal Overall strut system moves downward. 2. RH2 - Base PI under the SST tends to bend the SST strut upward. 3. RH2 - SST on the PI also tends to bend the circuit strut upward. 4. RH2 features counters the downward movement of the Nominal case. 14

Many samples can be measured against a control group Main Chamber Main Chamber provides temperature

15 Test Data Daughter Chamber Daughter Chamber with no vibration to measure PSA/RSA connected to the main chamber Many samples can be measured against a control group Main Chamber Main Chamber provides temperature and humidity controlled environment PSA change (deg.) A (no coverlay) B C (no coverlay) D E Comparison of similar designs with the circuit materials available. 15

16 Comparison of Model and Measurement PSA change (deg.) Model Measurement A B C D E Different CHE material properties In general, the model calculation is consistent with the measurement. 16

17 Concluding Remarks A study of humidity effect on PSA change has been conducted through a FE model. Some design explorations were presented. Showed that gimbal features can be designed to lower the impact of humidity substantially. Experimental comparison of similar designs revealed the wide range of material properties substantially affected the humidity impact on PSA. More robust gimbal in terms of humidity sensitivity can be achieved by using lower CHE polyimide material and by introducing effective humidity-resistant design features. 17

18 Acknowledgement Thanks to Magnecomp Precision Technology for the support of this project Thanks to MPT s Metrology Team in conducting the test and collecting data For questions, please contact: Peter Hahn <phahn@magnecomp.com> 18

Abstract. Tawin Phonpai and Thira Jearsiripongkul*

Abstract. Tawin Phonpai and Thira Jearsiripongkul* 435 Tawin Phonpai and Thira Jearsiripongkul* Abstract In this paper, an analysis of vibration of head gimbals assembly (HGA) in hard disk drive (HDD) with operational HDD are studied. ANSYS is used for