AN4211 Application note Guidelines for soldering MEMS microphones By Alessandro Morcelli Introduction This application note provides guidelines and recommendations for soldering MEMS microphones on application boards. Microphones, as pressure sensors, sense the mechanical stress coming from the PCB, hence this force should be kept to a minimum. Printing and stencil parameters, followed by device footprints/recommended land patterns, stencil openings, and process considerations are presented in this document. The following guidelines have been developed for the MEMS microphone family (MP45DT02/-M, MP34DB01, MP34DT01/-M, MP33AB01/H, MP34DB02, and MP23AB02B) offered by STMicroelectronics. Demonstration boards (STEVAL-MKI129Vx) for the evaluation and promotion of the MP45DT02, MP34DT01, and MP34DT01 are also available. Please refer to AN4184 "Microphone coupon boards STEVAL-MKI129Vx based on the MP45DT02, MP34DB01, and MP34DT01" on www.st.com for further information. Figure 1: Mechanical specifications for soldering June 2015 DocID023971 Rev 4 1/12 www.st.com Contents AN4211 Contents 1 Printing and stencil parameters ..................................................... 3 2 Device footprint, land pattern and stencil openings ..................... 4 2.1 MP45DT02 and MP45DT02-M dimensions ....................................... 4 2.2 MP34DB01 dimensions ..................................................................... 5 2.4 MP34DT01 and MP34DT01-M dimensions ....................................... 6 2.5 MP33AB01 and MP33AB01H dimensions ........................................ 7 2.6 MP34DB02 dimensions ..................................................................... 8 2.8 MP23AB02B dimension .................................................................... 9 3 Process considerations ................................................................ 10 4 Revision history ............................................................................ 11 2/12 DocID023971 Rev 4 AN4211 1 Printing and stencil parameters Printing and stencil parameters The soldering paste thickness and pattern are important for the proper microphone soldering process. Some recommendations to be followed are listed below: Stainless steel stencils are recommended Stencil thickness of 75 - 100 µm (2.95 - 3.94 mils) is recommended for screen printing The final soldering paste thickness should allow proper cleaning of flux residuals and clearance between the sensor package and PCB Stencil aperture should have a rectangular shape The openings of the stencil for the signal pads should be between 70 - 90% of the PCB pad Optionally, for better solder paste release, the aperture walls should be trapezoidal and the corners rounded The fine IC leads pitch requires accurate alignment of the stencil to the PCB. The stencil and printed circuit assembly should be aligned to within 25 µm (1 mil) prior to application of the solder paste DocID023971 Rev 4 3/12 Device footprint, land pattern and stencil openings AN4211 2 Device footprint, land pattern and stencil openings 2.1 MP45DT02 and MP45DT02-M dimensions Figure 2: MP45DT02 - device footprint and PCB land pattern Figure 3: MP45DT02 - recommended stencil openings 4/12 DocID023971 Rev 4 AN4211 2.2 Device footprint, land pattern and stencil openings MP34DB01 dimensions Figure 4: MP34DB01 - device footprint and PCB land pattern Figure 5: MP34DB01 - recommended stencil openings DocID023971 Rev 4 5/12 Device footprint, land pattern and stencil openings 2.4 AN4211 MP34DT01 and MP34DT01-M dimensions Figure 6: MP34DT01 - device footprint and PCB land pattern Figure 7: MP34DT01 - recommended stencil openings 6/12 DocID023971 Rev 4 AN4211 2.5 Device footprint, land pattern and stencil openings MP33AB01 and MP33AB01H dimensions Figure 8: MP33AB01 and MP33AB01H - device footprint and PCB land pattern Figure 9: MP33AB01 and MP33AB01H - recommended stencil openings DocID023971 Rev 4 7/12 Device footprint, land pattern and stencil openings 2.6 AN4211 MP34DB02 dimensions Figure 10: MP34DB02 - device footprint Figure 11: MP34DB02 - recommended stencil openings 8/12 DocID023971 Rev 4 AN4211 2.8 Device footprint, land pattern and stencil openings MP23AB02B dimension Figure 12: MP23AB02B - device footprint Figure 13: MP23AB02B recommended stencil openings DocID023971 Rev 4 9/12 Process considerations 3 AN4211 Process considerations If self-cleaning solder paste is not used, proper cleaning of the board after soldering must be done to remove any possible source of leakage between pads due to flux residues. For the soldering profile, refer to the table and figure below. Table 1: Soldering profile Description Parameter Average ramp rate Pb free TL to TP 3 °C/sec max Minimum temperature TSMIN 150 °C Maximum temperature TSMAX 200 °C Time (TSMIN to TSMAX) tS 60 sec to 120 sec Ramp-up rate TSMAX to TL 3 °C/sec max Time maintained above liquidus temperature tL 60 sec to 150 sec Liquidus temperature TL 217 °C Peak temperature TP 260 °C max Preheat Time within 5 °C of actual peak temperature 20 sec to 40 sec Ramp-down rate 6 °C/sec max Time 25 °C (t25 °C) to peak temperature 8 minutes max Figure 14: Soldering profile No solder material reflow on the side of the package is allowed since LGA packages have metal traces on the sides of the package. 10/12 DocID023971 Rev 4 AN4211 4 Revision history Revision history Table 2: Document revision history Date Revision Changes 12-Mar-2013 1 Initial release. 21-Jul-2014 2 Added Section 2.5: "MP34DB02 dimensions" and Section 2.6: "MP23AB02B dimension". 08-Aug-2014 3 Modified Figure 9: "MP33AB01 and MP33AB01H - recommended stencil openings". 15-Jun-2015 4 Updated Section "Introduction" Updated Section 2: "Device footprint, land pattern and stencil openings" DocID023971 Rev 4 11/12 AN4211 IMPORTANT NOTICE – PLEASE READ CAREFULLY STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, enhancements, modifications, and improvements to ST products and/or to this document at any time without notice. Purchasers should obtain the latest relevant information on ST products before placing orders. ST products are sold pursuant to ST’s terms and conditions of sale in place at the time of order acknowledgement. Purchasers are solely responsible for the choice, selection, and use of ST products and ST assumes no liability for application assistance or the design of Purchasers’ products. No license, express or implied, to any intellectual property right is granted by ST herein. Resale of ST products with provisions different from the information set forth herein shall void any warranty granted by ST for such product. ST and the ST logo are trademarks of ST. All other product or service names are the property of their respective owners. Information in this document supersedes and replaces information previously supplied in any prior versions of this document. © 2015 STMicroelectronics – All rights reserved 12/12 DocID023971 Rev 4