Is Now Part of To learn more about ON Semiconductor, please visit our website at

Transcription

1 Is Now Part of To learn more about ON Semiconductor, please visit our website at ON Semiconductor and the ON Semiconductor logo are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries. ON Semiconductor owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of ON Semiconductor s product/patent coverage may be accessed at ON Semiconductor reserves the right to make changes without further notice to any products herein. ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Buyer is responsible for its products and applications using ON Semiconductor products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information provided by ON Semiconductor. Typical parameters which may be provided in ON Semiconductor data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including Typicals must be validated for each customer application by customer s technical experts. ON Semiconductor does not convey any license under its patent rights nor the rights of others. ON Semiconductor products are not designed, intended, or authorized for use as a critical component in life support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should Buyer purchase or use ON Semiconductor products for any such unintended or unauthorized application, Buyer shall indemnify and hold ON Semiconductor and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that ON Semiconductor was negligent regarding the design or manufacture of the part. ON Semiconductor is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.

2 AN-6060 Guidelines on Leadforming, Trimming Lead Length, and Heatsink Mounting Introduction The ever-increasing demand for smaller consumer products often results in semiconductor designers manipulating package configurations to fit intended designs. More specifically, designs often require custom leadforming and module assembly practices for packages like the TO-262, TO-220, and TO-247. It is the intent of this application note to introduce general guidelines to ensure basic protection to the integrity of the package, both mechanically and electrically. Improper handling of devices can result in immediate or latent failures from cracked epoxy, epoxy delamination, die fractures, and bond-wire shearing. Fairchild Semiconductor tests the electrical integrity of the devices as supplied. Once leads and/or package configuration is altered from its original state, the integrity of the device cannot be guaranteed. The reliability of the package within the application becomes the responsibility of the designer. Leadforming In an effort to continually supply the industry with reliable semiconductor products, Fairchild Semiconductor recommends contacting to local sales representative if a modification in package configuration is desired. Fairchild has to ability to leadform most straight-lead packages to common configurations and will consider custom leadforming options. If it is necessary to perform leadforming processes, certain precautions should be taken to protect the integrity of the package. Failure to do so can have an adverse effect on the mold compound and lead interface. This initial damage combined with thermal stresses from soldering and operating conditions can damage the device. Such damage may include, but is not limited to; mold compound delamination (allowing for moisture ingression), fractured die, cracked mold compound, and sheared bond wires (resulting in intermittent or open connections). These failures could appear immediately at final test or may be latent and show up in the field. Some general guidelines to follow when leadforming are: Clamp all leads firmly and uniformly between the bend and the mold compound, ensuring that the clamp does not come in contact with the mold compound. The clamping area should be greater than the thickness of the leads. Clamp force should be greater than the force required to bend leads to desired form. Leads are normally deformed about 0.03mm to 0.05mm during clamping (see Figure 1). The bend should take place beyond the seating plane area of the lead. The bend radius (R) should always be greater than the thickness (T) of the lead terminal (see Figure 1). The leads should never be bent more than 90 degrees (see Figure 1). Device Clamp Spaced Should be wider than lead thickness R T Should never be bent more than 90 degrees Figure 1. Leadforming Leadforming should avoid dambar cut area. The bend radius should be formed outside that area. Change of material stiffness by uneven cross-section prevents smooth radius forming at dambar area (see Figure 2). Dambar area Figure 2. Leadforming Should Avoid Dambar Area Rev /19/07

3 The leads should never be bent laterally (sideways) (see Figure 3). Leads should NEVER be bent laterally Figure 3. Leadforming Should Avoid Lateral Bends The leads should never be bent more than once; this weakens the lead and has a thinning effect in that area. Ensure the body of the device is allowed to float free during the bending process. Failure to do so induces mechanical shock into the package through the leads. This can be verified through finite element analysis. When clamps come in contact with molding compound and clamping force is not strong enough to grip lead tightly (Figure 5), high stress is applied at lead and molding compound (Figure 7), while normal clamping does not create any stress in molding compound and adjacent lead (Figure 4 and Figure 6). Molding compound Clamp Lead Force Force Figure 4. Normal Leadforming Figure 5. Abnormal Leadforming (Clamps Contact Molding Compound) Figure 6. Stress Distribution, Normal Figure 7. Stress Distribution, Abnormal Rev /19/07 2

4 Leads must be formed prior to fixing them to a printed circuit board or heatsink. No additional bending of the leads should occur when the device is being inserted into the circuit board. (see Figure 8, Figure 9, Figure 10). Heatsink Solidly affixedtoheatsink PCB Solder joint Figure 8. Package Mounted on Heatsink and PCB Leads should not be stressed in any direction Figure 9. Correct Placement Figure 10. Incorrect Placement Manually bending leads should be avoided. If necessary, all rules above apply. The use of smooth jaw, non-tapered needle-nose pliers is recommended. Equipment utilized to perform bending should be properly maintained to ensure all rules are followed. Ensure the dimensions of the leadform allow the device to rest against the heatsink (if used) with no stress applied to the leads. Ensure allowance is made for sil pad or thermal compound. Large packages, such as the TO-247, are not recommended for applications requiring leadforming. Rev /19/07 3

5 Trimming Lead Length Just as precautions should be taken during the leadforming process, similar guidelines need to be followed when cutting the leads. Clamp leads firmly and uniformly between the cut and the mold compound, ensuring the clamp does not come in contact with the mold compound (see Figure 11). Ensure the body of the device is allowed to float free during the cutting process. Failure to do so induces mechanical shock into the package through the leads. Equipment utilized to perform trimming should be properly maintained to ensure all points above are followed. Cutting tool life should be known. A cutting count should be in place and tool edges replaced after recommended life span. Blade Figure 11. Trimming Device Clamp Fixed blade Heatsink Mounting The use of heatsinks is often required to maintain thermal stability within an application. This section addresses precautions that should be taken to avoid mechanical damage to the device. The surface of the heatsink should be smooth, flat (within 2 mils across mounting surface), and clear of foreign material. The mounting hole in the heatsink should be free of burrs and have no cratering occurring around the hole. Proper application of thermal grease should be applied to fill in any irregularities and decrease the thermal resistance. Caution should be used when using sil-pads or pads of other materials. Thick pads used along with screws can cause uneven torquing and result in die stress/fractures. When using screws on tabbed devices (T0-220) it is advisable to use a torque-spreading mechanism to spread pressure across the entire tab. As a minimum, a washer is acceptable as long as it does not make contact with the mold compound of the device. When the device is mounted on the heatsink and is in position on the circuit board, there should be no strain on the leads of the device in any direction (see Figure 8, Figure 9, Figure 10). Proper care should be taken not to over-torque the device. Over-torquing provides no additional thermal gains and can have adverse effects on the silicon within the package. Spring clips can be utilized for attaching devices to heatsinks. Proper care should be taken when installing clips. Sudden shock, by snapping the clip on the device, can cause damage to the silicon within the package. The heatsink should be rigidly mounted to the circuit board so the weight of the device/heatsink combination is not supported by the leads. Devices should be mounted to heatsink prior to soldering leads to the circuit board. Leadforming, if needed, should be done prior to mounting. Rev /19/07 4

6 DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION, OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, or (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. Rev /19/07 5

7 ON Semiconductor and are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries. ON Semiconductor owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of ON Semiconductor s product/patent coverage may be accessed at Marking.pdf. ON Semiconductor reserves the right to make changes without further notice to any products herein. ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Buyer is responsible for its products and applications using ON Semiconductor products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information provided by ON Semiconductor. Typical parameters which may be provided in ON Semiconductor data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including Typicals must be validated for each customer application by customer s technical experts. ON Semiconductor does not convey any license under its patent rights nor the rights of others. ON Semiconductor products are not designed, intended, or authorized for use as a critical component in life support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should Buyer purchase or use ON Semiconductor products for any such unintended or unauthorized application, Buyer shall indemnify and hold ON Semiconductor and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that ON Semiconductor was negligent regarding the design or manufacture of the part. ON Semiconductor is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner. PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT: Literature Distribution Center for ON Semiconductor E. 32nd Pkwy, Aurora, Colorado USA Phone: or Toll Free USA/Canada Fax: or Toll Free USA/Canada orderlit@onsemi.com Semiconductor Components Industries, LLC N. American Technical Support: Toll Free USA/Canada Europe, Middle East and Africa Technical Support: Phone: Japan Customer Focus Center Phone: ON Semiconductor Website: Order Literature: For additional information, please contact your local Sales Representative