Yu-Hung Shiau <yshiau@ATPUS To: [log in to unmask] A.COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Sent by: Aero/ST Group) TechNet Subject: [TN] IPC SM-782 on-line calculator <[log in to unmask] ORG> 11/27/01 06:53 AM Please respond to "TechNet E-Mail Forum." Land Pattern calculation is still an artform, not a science and depends on a number of parameters such as board material, component package (often manufacturer-specific), assembly process to be used (Wave or CR, etc), P&P machines being used to populate the boards and your own design rules. I raised this issue on TechNet a few weeks ago, especially since I was getting different answers for land pattern sizes depending on which method I used ( component data sheets, SM-782 or calculators). IPC stated that they are working to address these issues. However, to answer your specific questions, see comments below, PLUS the 4 main factors to consider are the board manufacturing tolerence, the component placement tolerence and the tolerence of the component itself, as well as the component's actual lead:board contact area and component dimensions. If you have any experience of determining land patterns that work, use that background to judge the "reasonableness" of the calculated results. For example, the larger allowance between heel and toe has to go to the end where max stress is going to be experienced. Usually this is the end where the lead goes on to join the component body, if you follow. Hi, Does anyone know how to use the on-line SM-782 calculator? There are few fields I don't know what numbers should I plug in. 1-1. Man. Allowance- P Place Accuracy **FIND OUT FROM YOUR ASSEMBLY PEOPLE WHAT THE PLACEMENT ACCURACY IS OF THE PICK AND PLACE MACHINES THEY USE AND PLUG THAT FIGURE IN.** 1-2. Man. Allowance- J/T Toe Min. ** FROM YOU FAB HOUSE, OBTAIN THE PAD POSITIONAL TOLERENCE THEY ARE WORKING TO WHEN FABRICATING THE BOARDS AND PLUG THAT FIGURE IN.** 2-1. Solder Joint Design Goal- J/T Toe Min **IN THE ABSENCE OF COMPONENT DATA SHEET INFORMATION OR SPECIFIC DATA FOR THE PACKAGE FROM SM-782, MIN. TOE ALLOWANCE CAN BE TAKEN FROM TABLE 3.4 (NEAR THE FRONT) OF SM-782. I DON'T BELIEVE IT'S ACCURATE FOR ALL PURPOSES, BUT IT'S THE BEST AVAILABLE IN THE ABSENCE OF ANY OTHER INFO.** 2-1. Solder Joint Design Goal- J/H Heel Min ** SAME AS FOR TOE-TAKE FROM THE SPEC TABLE** 2-1. Solder Joint Design Goal- J/S Side Min ** SIDE ALLOWANCE DEPENDS ON THE COMPONENT PITCH AND LAND SPACING REQUIREMENTS OF THE DESIGN. FIND A COMPROMISE BETWEEN YOUR DESIGN RULES AND THE REQUIREMENTS OF THE COMPONENT. OFTEN THE SIDE ALLOWANCE IS ZERO BECAUSE THERE ISN'T ROOM TO HAVE THE PAD ANY WIDER THAN THE COMPONENT LEAD, BUT ARE ALSO NOT MUCH LARGER IN MANY CASES THAN ABOUT 0.02MM. I THINK A SIDE ALLOWANCE IS ALSO GIVEN IN THE SPEC TABLE ** **IN SUMMARY, YOU HAVE YOU USE YOUR OWN BEST KNOWLEDGE/JUDGEMENT TO OBTAIN THE FINAL PATTERN. DON'T MAKE THEM TOO LONG AT EITHER END, OR TOO SHORT EITHER, BUT DETERMINING WHAT IS TOO LONG AND WHAT IS TOO SHORT COMES DOWN TO EXPERIENCE, TRIAL AND ERROR.** I have lost my hard copy of my IPC SM-782 standard for a while. **I DON'T HAVE A COPY OF THE SPEC TO HAND EITHER, OR I WOULD BE ABLE TO REPRODUCE THE TABLE FOR YOU - IT'S NOT VERY LARGE.** By the way, which category I should go for the resistor array (resistor network) while I use the SM-782 calculator? **SORRY, CAN'T HELP YOU HERE** Thank you all for any feedback. YH Shiau Best of luck Peter Duncan --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 --------------------------------------------------------------------------------- [This e-mail is confidential and may also be privileged. If you are not the intended recipient, please delete it and notify us immediately; you should not copy or use it for any purpose, nor disclose its contents to any other person. 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