Technical FAQ's - PCB Power

Technical FAQ's

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PCB Fabrication

WHAT DOES SCORING MEAN?

This is a “v” groove cut into the top and bottom surface of an array of multiple PCB’s or between a board and rails to be removed after assembly. The cut is usually 1/3 top, 1/3 bottom, leaving 1/3 uncut in the middle. This process is used when removing the tabs of a tab route is not a viable option, this does result in a less smooth finished board edge. The boards are typically set up side by side and end to end with the edges adjacent to each other. After assembly the boards are broken or snapped apart.

WHAT IS THE MINIMUM REQUIRED CLEARANCE FROM THE PCB EDGE TO CONDUCTIVE PATTERN (COPPER) IN CASE OF MILLING OR SCORING?
PCB Edge

PCB edge to conductive clearance is required to prevent short to the chasis and also to provide the insulation to conductive elements of the board.

For outer layers :

Minimum clearance from PCB edge to copper (milling line): 0.30 mm
Minimum clearance from PCB edge to copper (V-cut line): 0.50 mm

For Inner layers :

Minimum clearance from PCB edge to copper (milling line): 0.50 mm
Minimum clearance from PCB edge to copper (V-cut line): 0.50 mm

WHICH SURFACE FINISH IS BETTER?

Generally customer specifies the surface finish. Although each surface finish has its benefits and limitations, several finishes are coming to the front of the pack to meet today’s advanced assembly needs.

HASL

  • More cost effective.
  • Most commonly requested finish.
  • Good shelf life. 268739
  • Quality compared to other finishes is lower.
  • Does not provide coplanar surface.
  • Not desirable for BGA and fine pitch SMT packages.
  • Its process introduces thermal excursion.

Immersion Silver

  • More industry accepted finish.
  • Provides a flat/planar surface.
  • Good for soldering fine pitch devices like QFPs and BGAs.
  • Does not subject the PCB to aggressive thermal excursion.
  • Good shelf life.
  • More cost effective compared to gold.
  • Handling, storage and assembly requires to follow some special guidelines.

ENIG (Electroless Nickel Immersion Gold)

  • Second most commonly requested finish.
  • Provides a flat/planar surface.
  • Highly solderable.
  • Fairly good shelf life.
  • The Nickel plating prevents Gold and Copper intermetallic migration.
  • Aesthetically very pleasing finish.
  • Difficult in controlling.
  • Could have compatibility issues with few solder mask types.
  • Highest costly surface finish of the group.

IF IN CASE I TAKE CARE OF MY DESIGN FOR IMPEDANCE CALCULATIONS AND CHOOSE THE SPECIAL LAYER STACK UP THEN DO I NEED TO GIVE ALL THE IMPEDANCE DETAIL TO THE MANUFACTURER?

Yes, if you give all the impedance detail, we will help you to decide the best possible stack up. And if you have already given the stack up detail, we will verify the stack up detail against impedance requirement and also we will make sure that you will get the required impedance in the finished PCBs.

If we get the impedance details, we are not only verifying the calculations again but we are generating an additional coupon for your boards and process those coupons along with your boards on a same production panel and after the production is finished, we separate those coupons from the panel and measure the impedance requirement on that coupon with the polar instrument and also if required we are doing destructive testing also. And if we are not getting the satisfactory results on the coupons, we will scrape the whole lot and we relaunch your job without any additional charges and do the required changes needed in the production and will deliver the PCBs once we get the satisfactory results on the coupons.

All this is possible only if you give the complete impedance details otherwise we will produce the PCBs as requested by you with the chosen stack up only and we will not take care for the other parameters.

Imp_Cal
HOW DO I AVOID/MINIMIZE EXCEPTIONS FROM PCB POWER WHILE DESIGNING MY PCB?

All queries that are not affecting your design are not always stupid queries. Know your manufacturer’s limitations and intension for asking such queries. Support him in smooth running of your job in the production.

You can avoid annoying questions by just attaching one readme file with the following details:

  • List of file identification.
  • Detail for the gerber format in case of gerber-d files
  • Detail of PTH / NPTH holes.
  • Details for any other special requirements.

And answers to frequently asked questions :

  • May we remove of non functional pads in inner layers?]
  • Adding copper thieving for better plating is allowed
  • Is there any logo placement restrictions]
  • May we add “teardrop” at trace and pad intersections?

PCB_Designing_Guideline

 

  • May we rim void if a land appears where a non-plated through-hole is placed?

PCB_Designing_Guideline

 

  • May we give gang opening to the fine pitch SMT packages if spacing does not permit for solder mask dam?

PCB_Designing_Guideline

 

  • If hole size tolerances are not called out, may we use +/- 0.075 mm?
  • If PCB thickness tolerances are not called out, may we use +/- 10%?
  • If PCB size tolerance is not called out, may we use +/- 0.25 mm?

Layout Service

WHAT ARE THE INPUTS REQUIRED TO AVAIL PCB LAYOUT SERVICE?

The inputs that are generally required for a PCB layout service are schematics and bill of material. We accept CAD schematics or even hand-drawn data or schematic in PDF format.

DO YOU SUPPORT MINOR CHANGES AFTER AN ORDER IS PLACED?

Yes, we do support changes in the previous version on the condition that they are well documented with the new schematic and BOM details.

DO YOU SUPPORT CONCEPT OF PCB DESIGNING?

We do not support PCB designing for now. If, however, you provide us with the schematic and BOM detail then we can definitely support as well as guide you wherever needed.

CAN YOU CONVERT OUR EXISTING FINISHED HOLE-DESIGN TO SURFACE MOUNT?

Yes, we can convert your existing finished hole-design to surface mount.

HOW WILL YOUR DESIGN TEAM GET IN TOUCH WITH US FOR ANY QUERIES / DOUBTS RELATED WITH THE RUNNING OF THE PCB LAYOUT?

Our design team will get in touch with you for the queries, if any, through a detailed mail attached with the screen shot or instead send you PDF files for approval of the component placement. We will also, support you through phone calls and TeamViewer.

WHAT IS SCHEMATIC?

Schematic is the pictorial representation of all the significant components and it’s inter connections within a circuit, a device or a project with the help of standard symbols. 

WHAT IS A BOM (BILL OF MATERIAL)?

A bill of material (BOM) is a comprehensive list of the components that are used in your schematic along with the detail of manufacturer’s parts, their number and quantity.

HOW DO I FIGURE OUT THE NUMBER OF LAYERS REQUIRED FOR MY DESIGN?

Use just 1 or 2 Layer PCB for the regular boards and 4 Layer PCBs for interfaces with controlled impedance (USB, Ethernet, LVDS). If you study the component datasheet, various component manufacturers suggest a similar layout guideline pointing out to the support of minimum layers and the number of signal and ground or power layer depending on the power supply and dielectric isolation requirement.

WHAT IS IMPEDANCE?

Impedance is a measure of the resistance against the flow of alternating current through a circuit.  It is usually expressed in ohms.

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