Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Dispensing Paste On 20 Pitch Pads

#6282

Dispensing Paste On 20 Pitch Pads | 23 August, 2000

Dr. Lee: What are the issues around dispensing solder paste on 20 pitch SMT device pads?

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Dr. Ning-Cheng Lee

#6283

Re: Dispensing Paste On 20 Pitch Pads | 23 August, 2000

For 20 mil pitch pads, the volume control is more critical in terms of bridging concern. In general, solder paste for dispensing is more prone to slumping due to low metal load and low viscosity. If the volume dispensed is on the high end, or if the paste break off at the end of dispensing is not a clean cut, the paste will tend to have bridging problem. If the paste is dispensed onto small pads for chip cap or chip resistor, tombstoning can be the issue if the solder paste on both ends is not equal in volume.

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#6284

Re: Dispensing Paste On 20 Pitch Pads | 24 August, 2000

How do these factors affect paste selection? How does paste selection affect nozzle slection?

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Dr. Ning-Cheng Lee

#6285

Re: Dispensing Paste On 20 Pitch Pads | 24 August, 2000

For 20 mil pitch applications, two important properties to evaluate are (1) dispensing volume consistency, (2) slump performance. As to the dispensing equipment, positive displacement will be the better choice for better consistency. Nozzle size is very much dictated by the smallest dot size you are shooting for.

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