While quality is always a primary concern, it is even more important in surface mount and micro-centerline applications. Tolerance build-up that was allowable in through-hole may not be acceptable because of the different soldering conditions encountered in surface mount. Following are the most critical measurements that are unique to surface mount interconnects, or that require special consideration in these applications.

Lead coplanarity is a measurement of the distance between the highest and lowest lead when the connector is sitting on a perfectly flat surface. Coplanarity of leads is critical for good solder fillets. Ideally, all leads should lie in the same plane because if even one lead is significantly higher or lower than the plane, it could lead to open solder joints. Most specifications call for coplanarity to be a maximum of 0.004 inch (0,10 mm) to .008 inch (0,20mm) deviation from the seating plane. For practical purposes, this means that the distance between the highest and lowest lead cannot exceed this amount. Coplanarity is a difficult and time consuming measurement. However, due to the critical nature of this specification, and the difficulty in maintaining it, it is very important that it be controlled through statistical sampling and quality assurance procedures. Laser measurement equipment accurate to within .000001 inch (0,000025mm) is available and can be employed for this purpose.