TSOP40 Lead pitch 0.50mm recommended aperture sizes?

Q1: What are the recommended stencil apertures for a TSOP40. Lead pitch 0.48mm & lead width 0.21mm. A1: We've talked about this previously here on SMTnet, for instance check the fine SMTnet Archives: http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=5872&#Message23258

Q2: And direction of squeegee print over the aperture? A2: It doesn't matter. Some anal people talk about printing fine pitch QFP on a diagonal

Q3: Recommended Stencil thickness? A3: Use proper aspect and area ratios. An example from the fine SMTnet Archives is: http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=1700&#Message7065

Q4: Recommended aperture reductions? A4: None

Q5: Recommended pcb pad sizes? A5: What ever the supplier recommends

Q6: Recommended Printer settings - pressures & speeds, or any suggestions (MPM AP)? A6: Get a different printer

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When printing below .5mm pitch, the recommended stencil thickness is 5Thou, laser cut. Do not use any reduction and ensure wherever possible the pad to space ration is 1:1, the length of the pad is not as important as the gap between adjacent pads. Typically, for 0.5mm the pad width should be 0.25 and the gap 0.25, also ensure that solder mask is present between the pads, it may flak off after reflow, and if this is the case do not worry it did the job it was intended to by preventing solder shorts. Print direction will depend on you speed and pressure, remember when printing the volume of past can be dictated by the relationship of the aperture to the direction of the squeegee, ie Parallel and Perpendicular printing.

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Mark,

You've already received some good advice from the other posters. The one thing I would add is that even if you solve your printing issues on this type of part, the relative small quantity of paste may be prone to soldering problems.

Ever see a board that has great soldering quality on a QFP 208 with a thin leaded part (TSOP) right next to it that is non-wetted? Some solder pastes are prone to drying out between the ramp and spike in the reflow cycle due to small (thin) deposits and a longer than needed ramp/soak stage. What you get is no flux vehicle left at the spike zone and non-wetting on the joints. I've had this problem on TSOPs using Amtech 259 RMA and Alpha 609 WS. Shortening the ramp/soak time was the cure in both cases.

This may be tangent to what you're after here but remember, it's free:)

Joe

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