MEMS麦克风制造的推荐焊接参数（即焊膏厚度）是多少？

嗨，
 
 
必须严格控制焊接参数，例如模板的厚度，最终焊膏厚度和平面度以及回流期间温度变化的速度，因为它们会对麦克风结构产生危险的副作用。不同的焊膏厚度可以在麦克风焊盘和封装上产生不同的力，并且过快的温度梯度可以对器件封装产生机械应力。
 
 •建议使用不锈钢模板
 •模板厚度为75 - 100μm（2.95 - 3.94 mils），建议用于丝网印刷
 •模板孔径应为矩形
 •信号焊盘模板的开口应在PCB焊盘的70-90％之间（每个ST麦克风的推荐模板开口如下图所示）
 •可选地，为了更好地释放焊膏，孔壁应为梯形，并且角部应为圆形
 •精细的IC引脚间距要求模板与PCB精确对准。在应用焊膏之前，模板和印刷电路组件应对准在25μm（1密耳）以内
 •最终的焊膏厚度应能够正确清洁焊剂残留物和传感器封装与PCB之间的间隙
 •填充模板开口的焊膏厚度必须尽可能均匀
 •必须遵循图21中所示的回流曲线
 •必须避免气相回流焊接过程，因为在蒸汽阶段，一些颗粒会进入声音入口并污染MEMS传感器
 •如果可能，建议在焊接过程中用泡沫或胶带密封麦克风端口孔
 •请勿使用任何超声波方法清洁PCB
 •应避免手动焊接，因为很难确保适当的温度梯度和温度随时间的变化
 有关详细信息（即焊盘图案，模板开口），请从ST网站下载应用笔记AN4211
 
 问候，
 亚历山德罗



以下为原文





Hi,


The soldering parameters such as the thickness of the stencil, the final soldering paste thickness and planarity and the velocity of the temperature change during the reflow must be rigorously controlled since they can produce dangerous side effects on the microphone structure. A different soldering paste thickness can generate different forces on microphone pads and on the package as well as an excessively fast temperature gradient can mechanically stress the device package.

• Stainless steel stencils are recommended
• Stencil thickness of 75 - 100 μm (2.95 - 3.94 mils) is recommended for screen printing
• 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 (The recommended stencil openings for each ST microphone are shown in the following figures)
• Optionally, for better solder paste release, the aperture walls should be trapezoidal and the corners rounded
• The fine IC lead 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  
• The final soldering paste thickness should allow for proper cleaning of flux residuals and clearance between sensor package and PCB
• The soldering paste thickness, filling the stencil openings, must be as homogeneous as possible
• The reflow profile depicted in Figure 21 must be followed
• The vapor phase reflow soldering process must be avoided since during the vapor stage some particles can enter in the sound inlet and contaminate the MEMS sensor
• If possible, sealing the microphone port hole with foam or with tape during the soldering process is recommended
• Do not clean the PCB with any ultrasonic method
• Manual soldering should be avoided since it is difficult to ensure the proper temperature gradient and temperature variation over time
For further details (i.e. land pattern, stencil openings) please download the application note AN4211 from the ST website  

Regards,
Alessandro