Ask Helena & Leo

Question: I have a bowed part on a bottom terminated part, and I’m trying to find the specification on such a part. Do you know the bow specification of IPC 7093, section 5.2.6 on max warp this part should be?

Answer: This question raised is knowing what the bow specification of IPC-7093, section 5.2.6 is all about.

First let’s look at the IPC-7093 document, Titled “Design and Assembly Process Implementation for Bottom Termination Components”. This is not a specification, it is an informational document on how to do the assembly and as stated in the SCOPE, states …”document describes the design and assembly challenges for implementing Bottom Termination surface mount Components (BTCs) whose external connections consists of metalized terminations that are an integral part of the component body”.

1.2 INTENT states …”although not a complete recipe, identifies many of the characteristics that influence the successful implementation of robust and reliable assembly processes and provides guidance information to component suppliers regarding the issues being faced in the assembly process”.

Now in section 5.2.6 Flatness (Bow and Twist) it discusses board flatness and how it is measured and what the percentages are and provides no further information.

To get the numbers for Bow and Twist, one needs to start with IPC-2221 ”Generic Standard for Printed Board Design” section 5.2.4 Bow and Twist. This is the first place the information is provided as it states …”Unless otherwise specified on the master drawing, the maximum bow and twist shall be 0.75% for boards that use surface mount components and 1.5% for all other board technologies. Panels that contain multiple printed boards to be assembled on the panel and later separated shall also meet these bow and twist requirements”.

The second place where the information is available is IPC-6012C-2010 “Qualification and Performance Specification for Rigid Printed Boards”, paragraph 3.4.3 Bow and Twist, which reiterates the information from IPC-2221.

IPC-2221 and 6012 are design and manufacturing specifications and when printed boards are fabricated they must be fabricated to the requirement of these two documents. IPC-6012 is also the performance specification which is used to measure all the attributes of the printed circuit board. IPC-A-600 also has Bow and Twist information and that information is also taken from the 6012 document.

Now to test for Bow and Twist one must go to IPC-TM-650 Method 2.4.22 and this document which is available as a free download from the IPC web page provides the information on how to do the physical test.