PCB Reliability: Via Design | EEWeb Community:
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Tuesday, May 23, 2017
Monday, May 22, 2017
Friday, May 19, 2017
Paste Stencil - Area Ratio Calculator
Area Ratio Calculator: Beam On
To achieve proper paste release from the stencil, an aperture's aspect ratio should be >1.5, and the area ratio should be >0.66. When the stencil separates from the board, paste release encounters a competing process; solder paste will either transfer to the pad on the board or stick to the aperture side walls. When the pad area is greater than 0.66 of the inside aperture wall area, a complete paste transfer should occur. Please see the below calculator which you can use to determine pad size for your aperture, and foil thickness of the stencil.
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To achieve proper paste release from the stencil, an aperture's aspect ratio should be >1.5, and the area ratio should be >0.66. When the stencil separates from the board, paste release encounters a competing process; solder paste will either transfer to the pad on the board or stick to the aperture side walls. When the pad area is greater than 0.66 of the inside aperture wall area, a complete paste transfer should occur. Please see the below calculator which you can use to determine pad size for your aperture, and foil thickness of the stencil.
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Thursday, May 18, 2017
Thursday, May 11, 2017
HDI (High Density Interconnect PCBs) - TTM Technologies, Inc.
"Advanced Capabilities: Microvias
A microvia maintains a laser drilled diameter of typically 0.006" (150µm), 0.005" (125µm), or 0.004" (100µm), which are optically aligned and require a pad diameter typically 0.012" (300µm), 0.010" (250µm), or 0.008" (200µm), allowing additional routing density. Microvias can be via-in-pad, offset, staggered or stacked, non-conductive filled and copper plated over the top or solid copper filled or plated. Microvias add value when routing out of fine pitch BGAs such as 0.8 mm pitch devices and below.
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A microvia maintains a laser drilled diameter of typically 0.006" (150µm), 0.005" (125µm), or 0.004" (100µm), which are optically aligned and require a pad diameter typically 0.012" (300µm), 0.010" (250µm), or 0.008" (200µm), allowing additional routing density. Microvias can be via-in-pad, offset, staggered or stacked, non-conductive filled and copper plated over the top or solid copper filled or plated. Microvias add value when routing out of fine pitch BGAs such as 0.8 mm pitch devices and below.
Additionally, microvias add value when routing out of a 0.5 mm pitch device where staggered microvias can be used, however, routing micro-BGAs such as 0.4 mm, 0.3 mm, or 0.25 mm pitch device, requires the use of Stacked MicroVias® using an inverted pyramid routing technique.
TTM maintains years of experience with HDI products and was a pioneer of second generation microvias or Stacked MicroVias (SMV®). SMV® Technology offers solid copper stacked microvias providing rout-out solutions for micro BGAs.
TTM developed and now offers an entire family of microvia technology solutions for your next generation products."
Source: HDI (High Density Interconnect PCBs) - TTM Technologies, Inc.:
Source: HDI (High Density Interconnect PCBs) - TTM Technologies, Inc.:
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Wednesday, May 10, 2017
BGA 800 PAD 0.4 mm pitch - FEDEVEL Forums
"This is the manufacturer we normally use at our company:
http://www.stevenagecircuits.co.uk/engineers
Different things need to be considering when working with such small clearances:
- Copper to copper clearance - probably the most obvious one. The value might need to be more on plated layers (top and bottom for example, but could be some others as well), since because of the plating they cannot achieve such a good accuracy. The values for plated and non-plated layers are normally given by the PCB manufacturer. It also depends which technology you want to use, for better technologies you are getting better values, but you pay more. With Stevenage we can get down to 50 um for none-plated layers and 76 um for plated layers using the most advanced technology.
- Track thickness - again it goes down to 50/76 um with the best technology offered by Stevenage.
- Minimum mechanical hole - concerns TH vias. Goes down to 0.15 mm. It is very important to know that this is the size of the drill piece they use to drill the holes. If in Altium you have 0.2 mm via hole for example, that is the finished hole diameter after plating. Because of the plating thickness, they always need to use a bigger drill size, so there is enough space for the plating and after the plating you will get a finished hole diameter of 0.2 mm as desired. With one of my boards they needed to use 0.3 mm drills for the 0.2 mm via holes. We were fortunate that this was not a problem with the particular board, but it could be in many cases. So always keep that in mind when you set up rules and work out clearances.
- Minimum laser hole - concerns micro vias. Goes down to 60 um. The aspect ratio (depth to diameter) is quite small with micro vias (as Robert explains well in the Advanced Layout course) and that should be always considered. With Stevenage it can be up to 1.3:1. That means that if you have a micro via with a hole diameter of 0.1 mm it can go a maximum of 0.13 mm in depth. That will normally be just the distance between two layers next to each other. If you decide to go with a very small micro vias (0.06 mm lets say) you might found that they can't be long enough to connect two layers in your stack.
- Minimum micro via pad - goes down to 188 um for the surface layer (top/bottom) and 138 um for inner layers. Using vias in pads helps to gain additional space as well, to do some routing on the top layer, but requires a more advanced technology and might lead sometimes to problems with successful soldering of the BGA.
- Minimum solder mask expansion/Minimum solder mask sliver. If you use too small of a value for the expansion, you risk some pads to be partially covered by solder mask after manufacturing. If you use too small of a value for the solder mask sliver, you risk getting shorts between pads. To prevent such problems, I found it is a good practice for example to cover (tent) vias which are underneath a BGA. With Stevenage the minimum expansion you can have is 25 um and the minimum sliver is 76 um.
Again all of that should be checked with the particular manufacturer prior to starting the design, since as Robert explained you might easily find that they either can't manufacturer the board or the yield could be pretty low."
Source: BGA 800 PAD 0.4 mm pitch - FEDEVEL Forums:
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http://www.stevenagecircuits.co.uk/engineers
Different things need to be considering when working with such small clearances:
- Copper to copper clearance - probably the most obvious one. The value might need to be more on plated layers (top and bottom for example, but could be some others as well), since because of the plating they cannot achieve such a good accuracy. The values for plated and non-plated layers are normally given by the PCB manufacturer. It also depends which technology you want to use, for better technologies you are getting better values, but you pay more. With Stevenage we can get down to 50 um for none-plated layers and 76 um for plated layers using the most advanced technology.
- Track thickness - again it goes down to 50/76 um with the best technology offered by Stevenage.
- Minimum mechanical hole - concerns TH vias. Goes down to 0.15 mm. It is very important to know that this is the size of the drill piece they use to drill the holes. If in Altium you have 0.2 mm via hole for example, that is the finished hole diameter after plating. Because of the plating thickness, they always need to use a bigger drill size, so there is enough space for the plating and after the plating you will get a finished hole diameter of 0.2 mm as desired. With one of my boards they needed to use 0.3 mm drills for the 0.2 mm via holes. We were fortunate that this was not a problem with the particular board, but it could be in many cases. So always keep that in mind when you set up rules and work out clearances.
- Minimum laser hole - concerns micro vias. Goes down to 60 um. The aspect ratio (depth to diameter) is quite small with micro vias (as Robert explains well in the Advanced Layout course) and that should be always considered. With Stevenage it can be up to 1.3:1. That means that if you have a micro via with a hole diameter of 0.1 mm it can go a maximum of 0.13 mm in depth. That will normally be just the distance between two layers next to each other. If you decide to go with a very small micro vias (0.06 mm lets say) you might found that they can't be long enough to connect two layers in your stack.
- Minimum micro via pad - goes down to 188 um for the surface layer (top/bottom) and 138 um for inner layers. Using vias in pads helps to gain additional space as well, to do some routing on the top layer, but requires a more advanced technology and might lead sometimes to problems with successful soldering of the BGA.
- Minimum solder mask expansion/Minimum solder mask sliver. If you use too small of a value for the expansion, you risk some pads to be partially covered by solder mask after manufacturing. If you use too small of a value for the solder mask sliver, you risk getting shorts between pads. To prevent such problems, I found it is a good practice for example to cover (tent) vias which are underneath a BGA. With Stevenage the minimum expansion you can have is 25 um and the minimum sliver is 76 um.
Again all of that should be checked with the particular manufacturer prior to starting the design, since as Robert explained you might easily find that they either can't manufacturer the board or the yield could be pretty low."
Source: BGA 800 PAD 0.4 mm pitch - FEDEVEL Forums:
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