Star InactiveStar InactiveStar InactiveStar InactiveStar Inactive
 

Example high-density PCB from a Sony Handycam DCR-TRV17E

The standard SMD footprints in, for example Eagle, are actually all too large, in the industry much smaller dimensions are used. Here's a PCB from 2001 that was made in large numbers. This PCB comes from a Sony DCR-TRV17 MiniDV Camcorder. I found it interesting because it contains many components in a small area. I wanted to know what the trace-width and other dimensions are:

Example high density HDI PCB
Example high-density HDI PCB

SnapEDA for ready-to-use PCB footprints and schematic symbols

While looking for footprint packages I discovered SnapEDA, very handy:

SnapEDA for ready-to-use PCB footprints and schematic symbols
SnapEDA for ready-to-use PCB footprints and schematic symbols

Minimum values for trace width and via size

Here are some standard minimum values for low cost PCBs which are used by PCB manufacturers:

Track width

6mil (Recommend >8mil)

Track/Vias space 

6mil (Recommend >8mil)

Pads space

8mil

Silkscreen text size

32mil

Drill hole

0.3mm

SMT Solder Mask Width

0.2mm

Solder Mask Clearance

0.2mm

Incidentally we may need a smaller trace width of 4mil, e.g. under ball grid chips.

PCB trace width and via drill used in smartphones, laptops etc.

  • Samsung GT-S5660 smartphone: Trace width 2mil, via diameter 12mil
  • Acer laptop 2008: Trace width 4mil
  • Sparkfun-samd21-mini-breakout: Trace width 10 and 6mil, via drill 10mil
  • Arduino-Zero-Pro-V3: Trace width 16 and 8mil, via drill 16mil

Where to make cheap high-density PCBs

Note that the price for a high-density prototype PCB may be much higher than for a standard PCB. For example, at pcbway, a standard PCB of 100x100mm costs just $5 with a minimum track/spacing of 6/6mil (0.24mm) and a minimum hole size of 0.3mm.

A high-density PCB with 3/3mil track/spacing and 0.15mm hole size, costs $170, which is 34 times more expensive, while the minimum dimensions are only halved.

If you take the minimum dimensions one step larger (4mil / 0.2mm), the price drops significantly to $64, see the example below:

PCB prototype price with 4/4mil track/spacing and 0.2mm hole size
PCB prototype price with 4/4mil track/spacing and 0.2mm hole size

AISLER in Germany

It was brought to my attention that AISLER in Germany makes PCB with minimum trace width of 0.1mm at a reasonable price.

AISLER PCB Design Rules
AISLER PCB Design Rules

How to choose resistor and capacitor SMD size

Note that the assembly of the small 0201 size is more expensive.

  • 0805 Very large and is not used much anymore.
  • 0603 The most used, also in laptops, except in smartphones. The advantage is the low assembly costs. You can still solder this size manually.
  • 0402 The most used in smartphones because of miniaturization.
  • 0201 This size is sporadically used in smartphones.
  • 01005 I have never seen this used.

PCB checklist

  • Carry out the Design Rule Check.
  • Check unconnected pins. In Eagle file > export Pinlist.
  • No traces under crystals and TO220.
  • Large pads for components that may need to be replaced.
  • Check if the Gerber files contain all layers, don’t forget Tdocument, Bdocument in Eagle.

Silkscreen text checklist

  • All text is vector
  • Pin1 at ICs, connectors and jumpers
  • PCB name and company name
  • Date or version
  • TS and BS
  • Name test pins

SO / SOIC package footprint pad size

The standard Eagle pad dimensions for SO-8, SO-14 etc. in Eagle are quite large: 26 x 80 mill, I prefer 26 x 60 mill or even smaller.

QFN package footprint pad length

Note the finger pad length for QFN footprints. The pad lengths in libraries, such as Eagle, are often too short, it protrudes too little outsite the package. That make it hard to make contact with the tip of a soldering iron when needed. It is then difficult to replace the QFN chip later.

QFN footprint path length too short
QFN footprint path length too short

This video demonstrates how to solder 0.5mm pitch QFN chips using only hot air and a soldering iron, without solder paste or a stencil.

Here is a video with another QFN soldering method.

QFN package solder absorption vias

When applying solder to the QFN package manually, the thermal pad easy gets too much solder. This causes that the distance to the PCB becomes too large, so the pins will not be soldered properly. To prevent this, there is a handy solution: add large vias, which absorbs the surplus of tin:

QFN package solder absorption vias
QFN package solder absorption vias

Online Gerber Viewer

Here you can upload the entire set of Gerber files in one go and see how the PCB looks like:
https://www.pcbway.com/project/OnlineGerberViewer.html

Online Gerber viewer Easyeda
Online Gerber viewer Easyeda

Adding breadboard pads to a prototype PCB

I always place extra pads on a prototype PCB, that allow easy modifications afterwards, see the PCB above. Use a dummy via: square 42mil, drill 20mil. Delete the via-solder mask, in Eagle you can do this by: Edit > change > Stop > set on and then select the via.

Using the PCB as a drilling jig for switches

It is difficult to precisely drill holes for switches in a front plate. I came up with a handy solution for that. Add a center hole in the middle of the switch, the PCB can then be used as a drilling jig:

 Tactile switch Eagle package with center hole

Cheap PCB manufacturing in China

I’m an inventor and regularly make electronics prototypes, nowadays this can be done with low costs in China. But many people already know this.

For example, a double-sided PCB of 10 x 10cm costs less than $10, including shipping. You will get always five pieces, even though you only need one. The PCB is completed with a solder mask and a silkscreen on both sides.

Make the first prototype PCB sloppy

The first prototype PCB can be designed quickly and sloppily. It is not necessary to spend time on aesthetics, it often has to be completely redesigned when many things change. During the development process you always get new ideas and insights. Designing fast and sloppy is however quite difficult for a precision neurotic as me.

 

Do you have any comments about the website? Please let me know.