Taiwan Semiconductor
Taiwan Semiconductor
Instruction Manual for TAIWAN SEMICONDUCTOR models including: 821-TSS42L, AN-1005, Discrete Semiconductors, 821-TSS42L AN-1005 Discrete Semiconductors, Semiconductors
7dlzdq 6hplfrqgxfwru 9huvlrq % í x / v } µ ] } v
File Info : application/pdf, 8 Pages, 1.95MB
DocumentDocumentAN-1005 Mounting and lead forming instructions for TO220 package www.taiwansemi.com Taiwan Semiconductor Content 1. Introduction.............................................................................................................................................................2 1.1 Purpose ..........................................................................................................................................................2 1.2 Scope ..............................................................................................................................................................2 2. The influence on mounting of To-220.....................................................................................................................2 2.1 Thermal Resistance ........................................................................................................................................2 2.2 Mechanical stress failure ................................................................................................................................3 3. Screw Mounting .....................................................................................................................................................4 4. Lead processes ........................................................................................................................................................ 5 3.1 Lead cutting ....................................................................................................................................................5 3.2 Lead bending ..................................................................................................................................................5 5. Soldering..................................................................................................................................................................6 Reference...................................................................................................................................................................... 7 1 Version: B2111 Taiwan Semiconductor 1. Introduction 1.1 Purpose The objective in this document is to discuss the mounting and lead forming for TO-220 package, and provide user the guideline for appropriate handling. 1.2 Scope The document describes the mounting considerations that contain screw torque mounting methods, lead forming process and soldering recommendation value in the application. 2. The influence on mounting of To-220 2.1 Thermal resistance The RJA is junction to ambient thermal resistance and it consists of many thermal resistances. The relationship between them is shown as following: RJA = RJC + RCH + RH + RHA RJC : Junction-Case thermal resistance RCH : Case-Heatsink thermal resistance RH : Heatsink thermal resistance RHA : Heatsink-Ambient resistance RJC RCH RH RHA Fig 1. Thermal resistance structure The contact surface between device and heatsink significantly affect thermal performance. The bad contact can cause air gap between them and thermal resistance can be increased. When the device's heat cannot be effectively transferred to heatsink, it might cause excessive heat to damage the device. Hence, the mounting torque is importance in application. If the torque is too low, the thermal resistance can be increased due to it doesn't provide enough contact pressure. If the torque is too 2 Version: B2111 Taiwan Semiconductor high, the pressure may cause product deformation and it is not helpful to reduce thermal resistance. Furthermore, the heatsink flatness should be considered. The bumpy or unclear heatsink can result in uneven contact surface and the air gap between them that can increase the thermal resistance. Fig 2. Uneven contact surface 2.2 Mechanical stress failure The improper mounting process or uneven contact surface can cause external mechanical stress on device. The high mechanical stress may cause some issue on the device, such as die crack, package crack and inner delamination. The following examples are failure samples for unsuitable mounting process. For this case, the serious crack can be observed on package by visual inspection. The failure is due to the excessive stress on device. (a) Back side of lead frame crack (b) Mold compound crack Fig 3. Package crack The other case, the device's electrical characters test data are abnormal. After de-cap it, the finding indicate that the die has some cracks. According to die crack direction analysis, the failure is the result of improper screw mounting process. Fig 4. Die crack 3 Version: B2111 Taiwan Semiconductor 3. Screw Mounting When two objects are fastened together using a nut and a screw, it can create the axial tension. The axial tension is also called tightening force that is difficult to measure. In general, the torque control is applied for screw fastening and can be carried out easily. The relationship between torque and axial tension is given by following formula. The different thread or size of screw can influence the tightening force. It needs to refer to the screw datasheet to estimate the clamp force. T T : Torque K : Torque coefficient F d : Normal size of screw F : Axial tension = KdF Fig 5. The relationship between torque and axial tension Screw mounting is a traditional assembly method accomplished with fastening a screw, nut and washer. As mentioned in the previous section, it needs to provide appropriate torque to minimize thermal resistance and avoid excessive mounting torque to damage the device. Screw Plain Washer Insulating Bush Device Insulator Heatsink Lock washer Nut Fig 6. Screw mounting of TO-220 The following lists are recommendations for mounting process: The mounting torque is recommended to be 0.9Nm (for M3 pitch 0.5mm) Self-tapping screws should not be used. The metallic washer between the screw head and the device tab is recommended to reduce the stress. Device attach to the heatsink before soldering in order to avoid shearing stress to damage the die during fastening 4 Version: B2111 Taiwan Semiconductor 4. Lead processes 4.1 Lead cutting The TO-220 lead can be cut before mounting or after mounting and soldering. When cutting after soldering, the harsh mechanical mishandling during cutting that could cause external stress to damage solder joint, but generally does not harm component body. When cutting before mounting, the leads have to be fixed firmly by a clamp (see Fig 8). 4.2 Lead bending Improper bending or lead forming can cause many problem, such as the die damage , the internal connection delamination or micro cracking on the solder plating of leads to expose the copper. In order to prevent those problems, the lead forming guideline is provided as following: Leads must be formed before mounting on a PCB or a heatsink. For manual lead bending, an un-tapered snipe-nose plier is recommended for fixture; see Fig 7. Clamp the leads firmly between the package body and the bend point. This way can relieve tensile stress during bending process and prevent component body damage; see Fig 8. TO-220 package have wider leads near package body, the bending distance L needs to be longer than the distance between the package body to narrow lead portion; see Fig 8. Bend radius R should not less than the thickness of the lead T; see Fig 8. The leads should not be bent at an angle of more than 90°; see Fig 8. Do not bend the leads laterally; see Fig 9(a). Do not bend directly at the edge of the package; see Fig 9(b). (a) Correct method (b) wrong method Fig 7. Manual lead bending Fig 8. Lead forming and cutting 5 Version: B2111 Taiwan Semiconductor (a) Bend the leads laterally. (b) Bend directly at the edge of the package. Fig 9. Incorrect lead bending methods 5. Soldering Wave soldering is reliable method for assembly that is typically used for soldering through-hole component. Dual wave soldering is common method for wave-soldering (see Fig. 10). The durations, ramp rates and max temperature are depended on the materials and the soldering equipment. According to JESD22-B106 definition for the heat resistance of solder wave. The recommended max value is 260°C, the sum of first and second wave should be less than 10s [1]. Fig.10 Dual wave Solder profile 6 Version: B2111 Taiwan Semiconductor Reference [1] JEDEC Solid State Technology Association: JESD22-B106. "Resistance to Solder Shock for Through-Hole Mounted Devices., 2005. Authors Fengcai Song : Application Engineer : Fengcai@mail.tsyew.com.cn Reyn Qin HL Lin : Site Engineering Manager : Reyn.Qin@mail.tsyew.com.cn : Product Application Manager : hl_lin@mail.ts.com.tw Taiwan Semiconductor Co., Ltd. Headquarters Address: 11F. No. 25 Sec. 3, Beishin Rd, Shindian District, New Taipei City, Taiwan R.O.C. Telephone: +886-2-8913-1588 E-mail: marketing@mail.ts.com.tw Website: www.taiwansemi.com 7 Version: B2111