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Volume and average height of solder paste after printing machine

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#56784

Volume and average height of solder paste after printing machine | 2 October, 2008

I'm new to SMT. Now, i'm making program for SPI machine to inscpect for solder paste of SP60-MU. I think this is a very good printer but some times, my program shows only 50-60% of volume transfer; and the average height is very high: nearly 200 pct. I dont know what's the problem. Can any body tell me, normally,what value of volume and average height is? how do you count average height from volume? Thanks.

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#56793

Volume and average height of solder paste after printing machine | 2 October, 2008

Hello Ok there is not much info here. What you have to mae sure of is several key factors. 1. Have you entered the correct stencil thickness. 2. Are you using the stencil gerber (not the paste layer) The paste layer is usually not adjusted for appeture adjustment. 3. Does the machine you are using have zero offset adjustment in the programing and are you using it. 4. the last is what is the appeture ratio. This is the wall hieght to the appeture area. If you are doing very small appetures on a thick stencil the paste release can be very low due to higher surface tension on the stencil than the board.

Jerry

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#56798

Volume and average height of solder paste after printing machine | 2 October, 2008

Are you using a Synapse 3D Master 3000neo Desktop SPI Machine?

We clipped the following from a article on solder paste inspection. It describes the setup of a paste inspection machine. [Solder Paste Measurement: A Yield Improvement Strategy That Helps Improve Profits; M Riddle; ASC International; SMT Express; V. 3, No. 5, May 17, 2001]

"The first step is to identify the variables in paste printing that have the greatest impact on first-pass yield and determine the targets and acceptable ranges particular to your products and processes. As mentioned earlier, most experts agree solder paste height and volume are the most critical characteristics. * If you are unsure of the appropriate specifications, start with targets based on the stencil thickness (for height) and stencil thickness times the aperture size (for volume). * Set reasonable upper and lower control limits (+ 25% and -25 % of the targets, for example). * Next, check the printer set-up by printing and measuring a test print on a flat sample surface. A piece of white poster board will work. Take sample measurements at critical locations (the corners of fine pitch sites, BGA and �BGA sites, etc.) in addition to gathering readings at the corners and the middle of the complete print area, checking for parallelism. * Once you are confident in the printer set-up, perform a pilot run. Record measurements on every PCB in the pilot lot. * If a print failure is found (ie exceeding your selected control limits) wash the sample, adjust the printer and reprint. Process the boards through reflow. * After reflow, inspect and calculate the yield. Adjust your process limits based on the defect analysis. ** For example, if post reflow inspection identifies shorts, lower the upper control limit. ** If opens are found, consider increasing your targets. * Don't be surprised if the targets based on the stencil design need to be revised. There may be several reasons for this, including PCB design, the thickness of solder mask, tin/lead plating on pads, reference surface used to calculate height, and board warp. * Remember, repeatability is the key to consistent results. Following this simple procedure to tune the process will put you on the right track to yield improvement."

Comments are: * You say, �� my program shows only 50-60% of volume transfer� => Is that accurate? If so, what are your aspect & area ratios? [Similar to the JerryS comment above.] * You say, � � and the average height is very high: nearly 200 pct.� => Our troop can make paste that height too. They snap the stencil-off a fast as the printer can go. It produces peaks on the top edges of the solder brick, because of the thixotropic nature of paste. Really speeds-up processing though. Yeh, right. * You say, � � solder paste of SP60-MU.� => What's a solder paste of SP60-MU? * You're talking about paste. How do these paste measurements relate to acceptable solder connections? Remember, your goal with this machine is to control process to aid in producing good solder connections that are consistant and repeatable.

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