Description

<style>.e_editor{font:14px/24px Roboto,Helvetica,Tahoma,Arial,'Microsoft YaHei','b8bf53';}.e_editor div,e_editor p,e_editor td,e_editor th,e_editor li{font-weight:inherit;font-size:inherit;font-style:inherit;font-family:inherit;}.e_editor ul{margin:-10px 0 20px;}.e_editor li{padding:5px 0;}.e_table{width:96%;border-collapse:collapse;empty-cells:show;}.e_table th,.e_table td{padding:5px;border:2px solid #eee;}.e_img{padding:10px 0;text-align:center;}.e_p{line-height:20px;padding:0 0 20px;text-indent:0em;}</style><p> The product I&#39;m running currently consist a mix of 20 mil pitch QFP, 50 mil pitch, 0402, BGA and variable size of connectors from small to big, on OSP finished PCB. Running intrusive reflow with a mix packages is a real headache, especially when you have to hv step up at certain location, where the clearance to the neighboring component ( 0402) is very limited. If I were to have a good DFM, what is the best clearance for the step up i.e. 12 mil from 6 mil thickness. FYI, the metal squeegee is purposely cut, to ensure flexibility at printing. </p><p> 2ndly, taking into consideration that the good solder wetting of OSP coated boards occurs only where the flux comes into contact with the pads, I&#39;ve modified the stencil opening for fine pitch i.e maintaining the length 1:1 and reduce the width by 2 - 4 mil from the pad size ( to prevent shorts). This is done with the intention of preventing the reflowed board from having an exposed copper ( small portion at the end/edge of the <a href="https://www.allpcb.com/soldermask/pads.html" target="_blank">copper pad</a> )but I failed to eliminate the pad with an exposed copper. Why is this happening and how should I overcome this problem. FYI, the experiment was also done with stncil aperture which purposely design longer than the pad length but still we tends to see a small portion of the pad at the edge end, exposed. </p><p> I&#39;ve explaind to the our customer about the OSP finised characteristic but they asked me why..and I kind of &quot;doinkk?&quot; To be honest, I&#39;m not happy with this &quot;exposed copper&quot; things, taking into consideration about the capillary action over the time. </p><p> I plan to go back to HASL, what do you guys think? Coplanarity issue should be minimal with 20 mil and above, rite ? Rather than touching-up every single point on the board, and induce other problem to the board. </p>