The following are requirements for the fabrication of the PC board assembly.
- Carrier card PCB pad-to-pad tolerance should be < ±25
µm.
The blue to red cross (surface pad to surface pad) tolerance with respect to the Gerber pad location should be less than ±1mil (25 µm).
- Carrier card assembly house placement capability should be < ±26 µm.
- RMS value of the PCB pad-to-pad and component placement tolerance, based on the capabilities listed above should be < ±36 µm.
- Samtec recommends a tolerance of ±0.04 mm in the distance between the connectors.
- The combination of all these requirements must be controlled to less than ±40 µm.
The evaluation of Samtec connector placement is conducted by shifting the placement of the connector from 0% (PCB pad center aligned with connector pin center) to 15% (pin center offset by 15% of PCB pad width). The shifted connectors are capable of self-aligning after a reflow soldering process. The following image shows that even though placement of the connector shifted by 15% of the pad width, the connector solder ball was still able to self-align to the center of pad.
Figure 1. Connector Pin/Pad Placement
Note: PCB fab and
assembly contractors must be able to produce carrier cards to the specifications
listed in the PCB Fabrication and Assembly House Requirements section. In
addition, the connectors that are shifted by 15% of the pad width must be capable of
self-aligning after a reflow soldering process.