PCB Libraries Forum : Questions & Answers https://www.PCBLibraries.com/forum/ Sun, 05 Apr 2026 07:51:28 +0000 Mon, 23 Mar 2026 08:46:09 +0000 http://blogs.law.harvard.edu/tech/rss Web Wiz Forums 12.07 30 https://www.PCBLibraries.com/forum/RSS_topic_feed.asp?FID=34 <![CDATA[PCB Libraries Forum]]> https://www.PCBLibraries.com/forum/forum_images/PCBLForumLogo.gif https://www.PCBLibraries.com/forum/ <![CDATA[Questions & Answers : How To Choose the Footprint for SMD Chip Resistor]]> https://www.PCBLibraries.com/forum/how-to-choose-the-footprint-for-smd-chip-resistor_topic3630_post14492.html#14492 Author: Tom H
Subject: How To Choose the Footprint for SMD Chip Resistor
Posted: 23 Mar 2026 at 8:46am

Here is the original EIA PDP-100 Chip Package dimensions and tolerances. 

https://www.pcblibraries.com/Forum/chips_topic3598.html

Compare with IEC.

]]> Mon, 23 Mar 2026 08:46:09 +0000 https://www.PCBLibraries.com/forum/how-to-choose-the-footprint-for-smd-chip-resistor_topic3630_post14492.html#14492 <![CDATA[Questions & Answers : How To Choose the Footprint for SMD Chip Resistor]]> https://www.PCBLibraries.com/forum/how-to-choose-the-footprint-for-smd-chip-resistor_topic3630_post14491.html#14491 Author: Ariel_Levy
Subject: How To Choose the Footprint for SMD Chip Resistor
Posted: 23 Mar 2026 at 12:58am

Tom thank you very much Smile
and thank you Feynman

My difficulty is in obtaining information the thickness of the contacts size of the component (the size "T")
I bought the IPC-7351 and 7352. and you don't have information about this.
I think to buy EIA-JEP95 , and don't know it's worth the money if very MFG design is contacts size what "he" want's.

This table i found is accurate?


How you handle this with general discrete components ,when the contacts size can be between 0.10 to 0.40?
With the IPC-7351 when contacts size is 0.4 mm?
]]> Mon, 23 Mar 2026 00:58:01 +0000 https://www.PCBLibraries.com/forum/how-to-choose-the-footprint-for-smd-chip-resistor_topic3630_post14491.html#14491 <![CDATA[Questions & Answers : How To Choose the Footprint for SMD Chip Resistor]]> https://www.PCBLibraries.com/forum/how-to-choose-the-footprint-for-smd-chip-resistor_topic3630_post14490.html#14490 Author: feynman
Subject: How To Choose the Footprint for SMD Chip Resistor
Posted: 22 Mar 2026 at 10:14am

Ask a/your assembler. They probably assembled millions of parts and are probably the best source for a reliable footprint.]]> Sun, 22 Mar 2026 10:14:58 +0000 https://www.PCBLibraries.com/forum/how-to-choose-the-footprint-for-smd-chip-resistor_topic3630_post14490.html#14490 <![CDATA[Questions & Answers : How To Choose the Footprint for SMD Chip Resistor]]> https://www.PCBLibraries.com/forum/how-to-choose-the-footprint-for-smd-chip-resistor_topic3630_post14489.html#14489 Author: Tom H
Subject: How To Choose the Footprint for SMD Chip Resistor
Posted: 22 Mar 2026 at 8:14am

IPC-7351 uses Min/Max Mode technology. the resulting footprint takes into consideration the package tolerances to calculate the pad stacks. The solder pattern should accommodate the package in the minimum, nominal and maximum material condition. 

The average 0402 tolerance range is +/-0.05 to +/-0.10. 

It seems like component manufacturers use their nominal package dimensions and add a Toe, Heel and Side. They use Nominal Mode technology and ignore the tolerances they provide in their datasheets. 

The average dimensions on an 0402 are L=1.00, W=0.50, T=0.25. 

Your pad stack pattern will depend on what dimensions and tolerances you use. 

However, if you run into a 0402 chip manufacturer that has tolerances greater than 0.10, I would highly question the accuracy of their machine process. 

Ideally, manufacturers try to produce packages that are Nominal Material Condition. That's the goal. Maybe in the future package tolerances will be 0.00 and then the Nominal Mode technology will take over and the IPC-7351 mathematical model will be history. 

]]> Sun, 22 Mar 2026 08:14:56 +0000 https://www.PCBLibraries.com/forum/how-to-choose-the-footprint-for-smd-chip-resistor_topic3630_post14489.html#14489 <![CDATA[Questions & Answers : How To Choose the Footprint for SMD Chip Resistor]]> https://www.PCBLibraries.com/forum/how-to-choose-the-footprint-for-smd-chip-resistor_topic3630_post14488.html#14488 Author: Ariel_Levy
Subject: How To Choose the Footprint for SMD Chip Resistor
Posted: 22 Mar 2026 at 5:07am

How do you choosethe footprint for SMD Resistor case 0402?

Vishay have3 recommendations for footprints.

Yageo onerecommended but it’s different from Vishay.

Vishay recommendation:

L=0.50 A=0.40 B=0.60

BASED ONIPC-7351

L=0.40 A=0.55B=0.60

BASED ON IEC 61188-6-2

L=0.55 A=0.35B=0.55

Yageo

L=0.50 A=0.50 B=0.60

 

I am very confused by all the recommendations.

I would appreciate a suggestion or any guidance on how to choose a footprint.


]]> Sun, 22 Mar 2026 05:07:04 +0000 https://www.PCBLibraries.com/forum/how-to-choose-the-footprint-for-smd-chip-resistor_topic3630_post14488.html#14488 <![CDATA[Questions & Answers : Chip Caps and Resistor w/No Terminal Tolerance]]> https://www.PCBLibraries.com/forum/chip-caps-and-resistor-w-no-terminal-tolerance_topic3627_post14482.html#14482 Author: Tom H
Subject: Chip Caps and Resistor w/No Terminal Tolerance
Posted: 11 Mar 2026 at 8:31am

When L and L1 dimensions are the same, only enter L (don't enter duplicate dimensions). 

L1 is optional if it's different than L. 

I recommend that you open the free SM Discrete.fpx file and sort the Case Code Column. 

Then search for similar Case Codes from other manufacturers and see what their Terminal Lead Tolerances are. 

Sometimes the component manufacturer will only provide the Minimum dimension and you need to figure out the Maximum dimension. 

Average Terminal Tolerances for chip components by Case Code:
  • 01005 - 0.03
  • 0201 - 0.05
  • 0402 - 0.10
  • 0603 - 0.15
  • 0805 - 0.20
  • 1206 - 0.25
  • 1812 - 0.30

]]> Wed, 11 Mar 2026 08:31:10 +0000 https://www.PCBLibraries.com/forum/chip-caps-and-resistor-w-no-terminal-tolerance_topic3627_post14482.html#14482 <![CDATA[Questions & Answers : Chip Caps and Resistor w/No Terminal Tolerance]]> https://www.PCBLibraries.com/forum/chip-caps-and-resistor-w-no-terminal-tolerance_topic3627_post14480.html#14480 Author: pcbfreedomcad
Subject: Chip Caps and Resistor w/No Terminal Tolerance
Posted: 11 Mar 2026 at 5:14am

What is entered in the tool for L and L1, when there is no tolerance for lead length given in the datasheet? 

I am thinking of Chip Capacitor and Resistor terminal tolerances. 

]]> Wed, 11 Mar 2026 05:14:19 +0000 https://www.PCBLibraries.com/forum/chip-caps-and-resistor-w-no-terminal-tolerance_topic3627_post14480.html#14480 <![CDATA[Questions & Answers : Thermal Pad and Paste Mask Apertures]]> https://www.PCBLibraries.com/forum/thermal-pad-and-paste-mask-apertures_topic3622_post14475.html#14475 Author: Tom H
Subject: Thermal Pad and Paste Mask Apertures
Posted: 05 Mar 2026 at 7:39am

All the Texas Instruments footprints on www.pcblibraries.com/POD that have thermal pads, have the exact checkerboard pattern dimensions and spacing as their datasheets provide. Including 0.05 mm corner radius. 

These parts include QFN, SON, QFP, SOP, PSON, PQFN, DPAK with thermal pads. There are approximately 40,000 TI footprints with thermal pads on the Parts on Demand cloud database. 

The only way to accomplish this is to build the footprint using the calculator and setup all the TI package and footprint dimensions and save to FPX for the 3D STEP model. 

Then move the footprint to FP Designer for customizing the paste mask apertures in the thermal pad stack. Then save to FPX as the real footprint. 

Rename the Calculator footprint and Physical Description to match the FP Designer data. 

Output to CAD the FP Designer footprint footprint first. Then open the Calculator footprint and create the 3D STEP only and overwrite the FP Designer 3D STEP model. 

Then import into your CAD tool and you'll get the perfect mfr. recommended pattern with a high-quality 3D STEP model. 

]]> Thu, 05 Mar 2026 07:39:00 +0000 https://www.PCBLibraries.com/forum/thermal-pad-and-paste-mask-apertures_topic3622_post14475.html#14475 <![CDATA[Questions & Answers : Thermal Pad and Paste Mask Apertures]]> https://www.PCBLibraries.com/forum/thermal-pad-and-paste-mask-apertures_topic3622_post14474.html#14474 Author: pcbfreedomcad
Subject: Thermal Pad and Paste Mask Apertures
Posted: 05 Mar 2026 at 3:19am

If a bottom pad of a QFN for example, has multiple paste mask openings generated from PCB Libraries, do these openings need to have rounded corners, or do the fabricators handle the issue with 90 degree corners on stencil openings automatically?

I know the bottom pad itself can have rounded corners.
]]> Thu, 05 Mar 2026 03:19:41 +0000 https://www.PCBLibraries.com/forum/thermal-pad-and-paste-mask-apertures_topic3622_post14474.html#14474 <![CDATA[Questions & Answers : PCB Model Select Radial (Dipped) Rect. 1]]> https://www.PCBLibraries.com/forum/pcb-model-select-radial-dipped-rect-1_topic3605_post14461.html#14461 Author: m.elsayed
Subject: PCB Model Select Radial (Dipped) Rect. 1
Posted: 24 Feb 2026 at 4:40am

you mean we can you Radial (Dipped) Rect for this part  For this part” 224MKP275KBG4” in this datasheet “"

http://download.siliconexpert.com/pdfs2/2023/5/12/0/10/38/943385/cde_/manual/mkp.pdf
please add more details why should use fp designer
]]> Tue, 24 Feb 2026 04:40:07 +0000 https://www.PCBLibraries.com/forum/pcb-model-select-radial-dipped-rect-1_topic3605_post14461.html#14461