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QUALIFICATION AND QUALITY ASSURANCE TEST AND COUPON FOR TQFP PACKAGES

IP.com Disclosure Number: IPCOM000008544D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2002-Jun-21
Document File: 4 page(s) / 227K

Publishing Venue

Motorola

Related People

Pradeep Lall: AUTHOR [+2]

Abstract

A new test board has been devised for the quality assurance and qualification of solder joints in TSOP and TQFP packages. The test board configuration uses the conventional lnstron pull test to concen- trate the test load in the solder joints and thus pref- erentially tests the quality of the solder connections.

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MOTOROLA Technical Developments

QUALIFICATION AND QUALITY ASSURANCE TEST AND COUPON FOR TQFP PACKAGES

by Pradeep Lall and Edwin Bradley

  A new test board has been devised for the quality assurance and qualification of solder joints in TSOP and TQFP packages. The test board configuration uses the conventional lnstron pull test to concen- trate the test load in the solder joints and thus pref- erentially tests the quality of the solder connections.

PROBLEM DEFINITION

  Traditionally, the mechanical reliability of BGA solder joints has been evaluated using the three- point bend test. The TQFPs are, however, not amenable to such a mechanical test criteria, mainly because the clearance between the package and the board will often result in package fracture before the solder joints are adequately stressed to evaluate defects. The only other method to evaluate the mechanical reliability of such solder joints quantita- tively is using a wirebond pull test type of machine. This method is also tedious and time consuming because of the process of hooking and pulling each lead. The possibility of damaging the leads during such a process cannot be ruled out.

THE INVENTION

A new test board has been designed, which will allow the differentiation between the good and

defective solder joints using the conventional Instron pull test. The board design is shown in Figure I. The TQFP is soldered onto the designed test board and each of the soldered package assem- blies can then be singulated and tested to evaluate the average pull strength of the solder joints. The main advantages of this technique include: much faster than the tedious pull test technique; the test uses the conventional lnstron type tensile test machine (similar to that used for the three point bend test) and does not require additional capital expense in terms of additional hardware for pull test; quantitative value of the solder strength can be

used to evaluate the effect of thermal shock. Figure 3 shows this test sample loading. The failure sites in all the sample was in the solder-the strength value is thus a true average value of the solder joint strength, unlike the pull test which, because of the smaller cross-section of the lead, often results in lead failure. The solder joint is thus often not tested in the pull test.

  Four boards with twelve 0.5 mm-144 pin TQFPs were subjected to 300 cycles of liquid-liquid thermal shock and pull tested to failure in the test coupon described in this report. A new test has been devised to serve as a quantitative indica...